Compounds are called complex, in the nodes of the crystals of which there are complexes (complex ions) capable of independent existence.

The value of complex compounds for various fields of technology is very high. The ability of substances to form complex compounds is used to develop effective methods for obtaining chemically pure metals from ores, rare metals, ultrapure semiconductor materials, catalysts, dyes, drugs, natural and waste water purification, scale dissolution in steam generators, etc.

The first complex compounds were synthesized in the middle of the 19th century. The founder of the theory of complex compounds was the Swiss scientist Werner, who developed in 1893 coordination theory . A great contribution to the chemistry of complex compounds was made by Russian scientists L.A. Chugaev, I.I. Chernyaev and their students.

Structure of complex compounds:

1. In each complex compound, inner and outer spheres. The inner sphere is called the complex. When writing chemical formulas of complex compounds, the inner sphere is enclosed in square brackets. For example, in complex compounds a) K 2 [BeF 4], b) Cl 2, the inner sphere is made up of groups of atoms - complexes a) [BeF 4] 2- and b) 2+, and the outer sphere is made up, respectively, by ions a) 2K + and b) 2Cl - .

2. In the molecule of any complex compound, one of the ions, usually positively charged, or an atom of the internal environment occupies a central place and is called complexing agent. In the formula of a complex (inner sphere), the complexing agent is indicated first. In the examples given, these are ions a) Be 2+ and b) Zn 2+.

The complexing agents are atoms or more often metal ions related to p-, d-, f- elements and having a sufficient number of free orbitals (Cu 2+, Pt 2+, Pt 4+, Ag +, Zn 2+, Al 3+, etc. ).

3. Around the complexing agent is located (or, as they say, coordinated) a certain number of oppositely charged ions or electrically neutral molecules, called ligands(or addends). In this case, these are a) F ions - and b) NH 3 molecules.

Anions F - , OH - , CN - , CNS - , NO 2 - , CO 3 2- , C 2 O 4 2- , etc., neutral molecules H 2 O, NH 3 , CO, NO and etc.

The number of coordination sites occupied by ligands around the complexing agent (in the simplest cases, the number of ligands surrounding the complexing agent) is called coordination number (c.h.) of the complexing agent. The coordination numbers of various complexing agents range from 2 to 12.

The most characteristic coordination numbers in solutions and the charge of the central ion (complexing agent) are compared below:

Note: The most common coordination numbers are underlined when two different types of coordination are possible.

In the considered examples, the coordination numbers of the complexing agents are: a) k.ch. (Be 2+) = 4, b) c.h. (Zn 2+) = 4.

B. Then they call the numbers and names of neutral ligands:

B. The last name is the complexing agent in the genitive case, indicating the degree of its oxidation (in brackets in Roman numerals after the name of the complexing agent).

For example, Cl is chlorotriammineplatinum (II) chloride.

If the metal forms an ion with one oxidation state, then it may not be included in the name of the complex. For example, Cl 2 is tetraamminzinc dichloride.

2. Name of the complex anion formed in a similar way, with the addition of the suffix "at" to the root of the Latin name of the complexing agent (for example, ferrate, nickelate, chromate, cobaltate, cuprate, etc.). For example:

K 2 - potassium hexachloroplatinate (IV);

Ba 2 - barium tetrarodanodiammine chromate (III);

K 3 - hexacyanoferrate (III) potassium;

K 2 - potassium tetrafluoroberyllate.

3. Names of neutral complex particles are formed in the same way as cations, but the complexing agent is called in the nominative case, and the degree of its oxidation is not indicated, because it is determined by the electroneutrality of the complex. For example:

Dichlorodiammineplatinum;

Tetracarbonyl nickel.

Classification of complex compounds. Complex compounds are very diverse in structure and properties. Their classification systems are based on various principles:

1. According to the nature of the electric charge, cationic, anionic and neutral complexes are distinguished.

A complex with a positive charge is called cationic, for example 2+, with a negative charge - anionic, for example 2-, with a zero charge - neutral, for example.

2. The types of ligands are:

a) acids, for example:

H is hydrogen tetrachloroaurate (III);

H 2 - hexachloroplatinate (IV) hydrogen;

b) grounds, for example:

(OH) 2 - tetraammine copper (II) hydroxide;

OH - diamminesilver hydroxide;

c) salt, for example:

K 3 - potassium hexahydroxoaluminate;

Cl 3 - hexaaquachromium (III) chloride;

d) non-electrolytes, for example, dichlorodiammineplatinum.

Formation of chemical bonds in complex compounds. To explain the formation and properties of complex compounds, a number of theories are currently used:

1) method of valence bonds (MVS);

2) the theory of the crystal field;

3) the method of molecular orbitals.

According to the MVS during the formation of complexes between the complexing agent and ligands, a covalent bond arises along donor-acceptor mechanism . Complexing agents have vacant orbitals; play the role of acceptors. As a rule, various vacant orbitals of the complexing agent are involved in the formation of bonds; therefore, their hybridization occurs. Ligands have lone pairs of electrons and play the role of donors in the donor-acceptor mechanism of covalent bond formation.

For example, consider the formation of the 2+ complex. Electronic formulas of valence electrons:

Zn atom - 3d 10 4s 2 ;

Zinc ion complexing agent

Zn 2+ - 3d 10 4s 0

As can be seen, the zinc ion at the outer electronic level has four vacant atomic orbitals close in energy (one 4s and three 4p), which will undergo sp 3 hybridization; the Zn 2+ ion, as a complexing agent, has c.h.=4.

When a zinc ion interacts with ammonia molecules, the nitrogen atoms of which have lone pairs of electrons (: NH 3), a complex is formed:

The spatial structure of the complex is determined by the type of hybridization of the atomic orbitals of the complexing agent (in this case, a tetrahedron). The coordination number depends on the number of vacant orbitals of the complexing agent.

In the formation of donor-acceptor bonds in complexes, not only s- and p-orbitals, but also d-orbitals can be used. In these cases, hybridization occurs with the participation of d-orbitals. The table below shows some types of hybridization and their corresponding spatial structures:

Thus, the MVS makes it possible to predict the composition and structure of the complex. However, this method cannot explain such properties of complexes as strength, color, and magnetic properties. The above properties of complex compounds are described by the crystal field theory.

Dissociation of complex compounds in solutions. The inner and outer spheres of a complex compound differ greatly in stability.

Particles located in the outer sphere are associated with the complex ion mainly by electrostatic forces (ionic bond) and are easily split off in an aqueous solution, like ions of strong electrolytes.

The dissociation (decay) of a complex compound into ions of the outer sphere and a complex ion (complex) is called primary. It proceeds almost completely, to the end, according to the type of dissociation of strong electrolytes.

For example, the process of primary dissociation during the dissolution of potassium tetrafluoroberyllate can be written according to the scheme:

K 2 [BeF 4] = 2K + + [BeF 4] 2-.

Ligands, located in the inner sphere of the complex compound, are associated with the complexing agent by strong covalent bonds formed according to the donor-acceptor mechanism, and the dissociation of complex ions in solution occurs, as a rule, to a small extent according to the type of dissociation of weak electrolytes, i.e. reversible until equilibrium is established. The reversible decay of the inner sphere of a complex compound is called secondary dissociation. For example, the tetrafluoroberyllate ion only partially dissociates, which is expressed by the equation

[BeF 4 ] 2- D Be 2+ + 4F - (secondary dissociation equation).

The dissociation of a complex as a reversible process is characterized by an equilibrium constant called the instability constant of the complex K n.

For the example in question:

K n - tabular (reference) value. The instability constants, whose expressions include the concentrations of ions and molecules, are called concentration constants. More stringent and independent of the composition and ionic strength of the solution are K n, containing instead of the concentration of the activity of ions and molecules.

The Kn values ​​of various complexes vary widely and can serve as a measure of their stability. The more stable the complex ion, the lower its instability constant.

Thus, among similar compounds with different values ​​of instability constants

the most stable complex is , and the least stable is .

Like any equilibrium constant, instability constant depends only on the nature of the complex ion, complexing agent and ligands, solvent, as well as on temperature and does not depend on the concentration (activity) of substances in solution.

The greater the charges of the complexing agent and ligands and the smaller their radii, the higher the stability of the complexes . The strength of the complex ions formed by the metals of the secondary subgroups is higher than the strength of the ions formed by the metals of the main subgroups.

The process of decomposition of complex ions in solution proceeds in many stages, with successive elimination of ligands. For example, the dissociation of the copper (II) 2+ ammonia ion occurs in four steps, corresponding to the separation of one, two, three, and four ammonia molecules:

For a comparative assessment of the strength of various complex ions, not the dissociation constant of individual steps is used, but the general instability constant of the entire complex, which is determined by multiplying the corresponding stepwise dissociation constants. For example, the instability constant of the 2+ ion will be equal to:

K H \u003d K D1 K D2 K D3 K D4 \u003d 2.1 10 -13.

To characterize the strength (stability) of complexes, the reciprocal of the instability constant is also used, it is called the stability constant (Kst) or the complex formation constant:

The equilibrium of dissociation of a complex ion can be shifted by an excess of ligands in the direction of its formation, and a decrease in the concentration of one of the dissociation products, on the contrary, can lead to the complete destruction of the complex.

Qualitative chemical reactions usually detect only outer sphere ions or complex ions. Although everything depends on the solubility product (SP) of the salt, the formation of which would proceed with the addition of appropriate solutions in qualitative reactions. This can be seen from the following reactions. If a solution containing a complex ion + is acted upon by a solution of any chloride, then no precipitate is formed, although a precipitate of silver chloride is released from solutions of ordinary silver salts when chlorides are added.

Obviously, the concentration of silver ions in the solution is too low, so that when even an excess of chloride ions is introduced into it, it would be possible to achieve the value of the solubility product of silver chloride (PR AgCl = 1.8 10 -10). However, after the addition of the potassium iodide complex to the solution, a precipitate of silver iodide precipitates. This proves that silver ions are still present in the solution. No matter how small their concentration, but it turns out to be sufficient for the formation of a precipitate, because. PR AgI \u003d 1 10 -16, i.e. much less than that of silver chloride. In the same way, under the action of a solution of H 2 S, a precipitate of silver sulfide Ag 2 S is obtained, the solubility product of which is 10 -51.

The ion-molecular equations of the ongoing reactions have the form:

I - D AgI↓ + 2NH 3

2 + + H 2 S D Ag 2 S↓ + 2NH 3 + 2NH 4 + .

Complex compounds with an unstable inner sphere are called double salts. They are designated differently, namely, as compounds of molecules. For example: CaCO 3 Na 2 CO 3; CuCl 2 ·KCl; KCl·MgCl 2 ; 2NaCl · CoCl 2 . double salts can be considered as compounds in the crystal lattice sites of which there are identical anions, but different cations; chemical bonds in these compounds are predominantly ionic in nature and therefore in aqueous solutions they dissociate almost completely into separate ions. If, for example, potassium chloride and copper (II) chloride are dissolved in water, then dissociation occurs according to the type of strong electrolyte:

CuCl 2 KCl \u003d Cu 2+ + 3Cl - + K +.

All ions formed in a double salt solution can be detected using appropriate qualitative reactions.

Reactions in solutions of complex compounds. The equilibrium shift in exchange reactions in electrolyte solutions involving complex ions is determined by the same rules as in solutions of simple (non-complex) electrolytes, namely: the equilibrium shifts in the direction of the most complete binding of ions (complexing agent, ligands, ions of the outer sphere), leading to to the formation of insoluble, poorly soluble substances or weak electrolytes.

In this regard, in solutions of complex compounds, reactions are possible:

1) exchange of ions of the outer sphere, in which the composition of the complex ion remains constant;

2) intrasphere exchange.

The first type of reaction is realized in those cases when it leads to the formation of insoluble and poorly soluble compounds. An example is the interaction of K 4 and K 3, respectively, with the cations Fe 3+ and Fe 2+, which gives a precipitate of Prussian blue Fe 4 3 and turnbull blue Fe 3 2:

3 4- + 4Fe 3+ = Fe 4 3 ↓,

Prussian blue

2 3- + 3Fe 2+ = Fe 3 2 ↓.

turnbull blue

Reactions of the second type are possible in those cases when this leads to the formation of a more stable complex, i.e. with a lower value of K n, For example:

2S 2 O 3 2- D 3- + 2NH 3.

K n: 9.3 10 -8 1 10 -13

At close values ​​of Kn, the possibility of such a process is determined by the excess of the competing ligand.

For complex compounds, redox reactions are also possible, which take place without changing the atomic composition of the complex ion, but with a change in its charge, for example:

2K 3 + H 2 O 2 + 2KOH \u003d 2 K 4 + O 2 + 2H 2 O.

complex compounds.

All inorganic compounds are divided into two groups:

1. first order compounds, ᴛ.ᴇ. compounds obeying the theory of valency;

2. connections of a higher order, ᴛ.ᴇ. compounds that do not obey the concepts of valency theory. Higher-order compounds include hydrates, ammoniates, etc.

CoCl 3 + 6 NH 3 \u003d Co (NH 3) 6 Cl 3

Werner (Switzerland) introduced into chemistry ideas about compounds of a higher order and gave them the name complex compounds. He referred to CS all the most stable compounds of a higher order, which in an aqueous solution either do not decompose into constituent parts at all, or decompose to a small extent. In 1893, Werner suggested that any element, after saturation, can also exhibit an additional valence - coordinating. According to Werner's coordination theory, in each CS there are:

Cl3: complexing agent (KO \u003d Co), ligands (NH 3), coordination number (CN \u003d 6), inner sphere, external environment (Cl 3), coordination capacity.

The central atom of the inner sphere, around which ions or molecules are grouped, is called complexing agent. The role of complexing agents is most often performed by metal ions, less often by neutral atoms or anions. Ions or molecules coordinating around a central atom in the inner sphere are called ligands. Ligands are anions: G -, OH-, CN-, CNS-, NO 2 -, CO 3 2-, C 2 O 4 2-, neutral molecules: H 2 O, CO, G 2, NH 3, N 2 H 4 . coordination number is the number of places in the inner sphere of the complex that are occupied by ligands. CN is usually higher than the oxidation state. CN = 1, 2, 3, 4, 5, 6, 7, 8, 9, 12. The most common CN = 4, 6, 2. These numbers correspond to the most symmetrical configuration of the complex - octahedral (6), tetrahedral ( 4) and linear (2). KCh envy on the nature of the complexing agent and ligands, as well as on the sizes of CO and ligands. Coordination capacity of ligands is the number of places in the inner sphere of the complex occupied by each ligand. For most ligands, the coordination capacity is unity ( monodentate ligands), less than two ( bidentate ligands), there are ligands with a higher capacity (3, 4, 6) - polydentate ligands. The charge of the complex must be numerically equal to the total outer sphere and opposite in sign to it. 3+ Cl 3 -.

Nomenclature of complex compounds. Many complex compounds have retained their historical names associated with the color or the name of the scientist who synthesized them. Today the IUPAC nomenclature is used.

Ion listing order. It is customary to call the anion first, then the cation, while the root of the Latin name KO is used in the name of the anion, and its Russian name in the genitive case is used in the name of the cation.

Cl is diamminesilver chloride; K 2 - potassium trichlorocuprate.

Order of listing ligands. The ligands in the complex are listed in the following order: anionic, neutral, cationic - without separation by a hyphen. Anions are listed in the order H - , O 2- , OH - , simple anions, complex anions, polyatomic anions, organic anions.

SO 4 - chloronitrsulfate (+4)

End of coordination groups. Neutral groups are named the same as molecules. The exceptions are aqua (H 2 O), amine (NH 3). The vowel ʼʼОʼʼ is added to negatively charged anions

– hexocyanoferrate (+3) hexaaminacobalt (+3)

Prefixes indicating the number of ligands.

1 - mono, 2 - di, 3 - three, 4 - tetra, 5 - penta, 6 - hexa, 7 - hepta, 8 - octa, 9 - nona, 10 - deca, 11 - indeca, 12 - dodeca, many - poly.

The prefixes bis-, tris- are used before ligands with complex names, where there are already mono-, di-, etc. prefixes.

Cl 3 - tris (ethylenediamine) iron chloride (+3)

The names of complex compounds first indicate the anionic part in the nominative case and with the suffix -at, and then the cationic part in the genitive case. At the same time, before the name of the central atom in both the anionic and cationic parts of the compound, all ligands coordinated around it are listed, indicating their number in Greek numerals (1 - mono (usually omitted), 2 - di, 3 - three, 4 - tetra, 5 - penta, 6 - hexa, 7 - hepta, 8 - octa). The suffix -o is added to the names of the ligands, and anions are first called, and then neutral molecules: Cl- - chloro, CN- - cyano, OH- - hydroxo, C2O42- - oxalato, S2O32- - thiosulfato, (CH3) 2NH - dimethylamino and etc. Exceptions: the names of H2O and NH3 as ligands are as follows: ʼʼaquaʼʼ and ʼʼamminʼʼ. If the central atom is part of the cation, then the Russian name of the element is used, followed by its oxidation state in brackets in Roman numerals. For the central atom in the composition of the anion, the Latin name of the element is used and the oxidation state is indicated before this name. For elements with a constant oxidation state, it can be omitted. In the case of non-electrolytes, the oxidation state of the central atom is also not indicated, since it is determined based on the electrical neutrality of the complex. Title examples:

Cl2 - dichloro-tetrammine-platinum(IV) chloride,

OH - diammine-silver(I) hydroxide.

Classification of complex compounds. Several different classifications of COPs are used.

1. by belonging to a certain class of compounds:

complex acids - H 2

complex bases -

complex salts - K 2

2. By the nature of ligands: aqua complexes, ammonia. Cyanide, halide, etc.

Aquacomplexes are complexes in which water molecules serve as ligands, for example, Cl 2 is hexaaquacalcium chloride. Ammineates and aminates are complexes in which the ligands are molecules of ammonia and organic amines, for example: SO 4 - tetrammine copper (II) sulfate. Hydroxocomplexes. In them, OH- ions serve as ligands. Especially characteristic of amphoteric metals. Example: Na 2 - sodium tetrahydroxozincate (II). Acid complexes. In these complexes, the ligands are anions-acidic residues, for example, K 4 - potassium hexacyanoferrate(II).

3. by the sign of the charge of the complex: cationic, anionic, neutral

4. according to the internal structure of the CS: according to the number of nuclei that make up the complex:

mononuclear - H 2, binuclear - Cl 5, etc.,

5. by the absence or presence of cycles: simple and cyclic CSs.

Cyclic or chelate (pincer) complexes. Οʜᴎ contain a bi- or polydentate ligand, which, as it were, captures the central atom M like cancer claws: Examples: Na 3 - sodium trioxalato-(III) ferrate, (NO 3) 4 - triethylenediamino-platinum (IV) nitrate.

The group of chelate complexes also includes intracomplex compounds in which the central atom is part of the cycle, forming bonds with ligands in various ways: by exchange and donor-acceptor mechanisms. Such complexes are very characteristic of aminocarboxylic acids, for example, glycine forms chelates with Cu 2+, Pt 2+ ions:

Chelate compounds are especially strong, since the central atom in them is, as it were, blocked by a cyclic ligand. Chelates with five- and six-membered rings are the most stable. Complexons bind metal cations so strongly that when they are added, such poorly soluble substances as CaSO 4 , BaSO 4 , CaC 2 O 4 , CaCO 3 dissolve. For this reason, they are used to soften water, to bind metal ions during dyeing, processing photographic materials, and in analytical chemistry. Many chelate-type complexes have a specific color, and in connection with this, the corresponding ligand compounds are very sensitive reagents for transition metal cations. For example, dimethylglyoxime [С(CH 3)NOH] 2 serves as an excellent reagent for Ni2+, Pd2+, Pt2+, Fe2+, etc. cations.

Stability of complex compounds. Instability constant. When the CS is dissolved in water, decomposition occurs, and the inner sphere behaves as a single whole.

K = K + + -

Along with this process, the dissociation of the inner sphere of the complex occurs to a small extent:

Ag + + 2CN -

To characterize the stability of the CS, we introduce instability constant equal to:

The instability constant is a measure of the strength of the CS. The smaller the K is, the more firmly the COP.

Isomerism of complex compounds. For complex compounds, isomerism is very common and there are:

1. Solvate isomerism is found in isomers when the distribution of water molecules between the inner and outer spheres is not the same.

Cl 3 Cl 2 H 2 O Cl (H 2 O) 2

purple light green dark green

2.Ionization isomerism is related to the different ease of dissociation of ions from the inner and outer spheres of the complex.

4 Cl 2 ]Br 2 4 Br 2 ]Cl 2

SO 4 and Br - sulfate bromo-pentammine-cobalt (III) and bromide sulfate-pentammine-cobalt (III).

C and NO 2 - chloride nitro-chloro-diethylenediamino-cobalt (III) initrite dichloro-diethylenediamino-cobalt (III).

3. Coordination isomerism found only in bicomplex compounds

[Co(NH 3) 6] [Co(CN) 6]

Coordination isomerism occurs in those complex compounds where both the cation and anion are complex.

For example, tetrachloro-(II)platinate tetrammine-chromium(II) and tetrachloro-(II)tetrammine-platinum(II) chromate are coordination isomers

4. Communication isomerism occurs only when monodentate ligands can be coordinated through two different atoms.

5. Spatial isomerism due to the fact that the same ligands are located around the CO or near (cis), or vice versa ( trance).

Cis isomer (orange crystals) Trans isomer (yellow crystals)

Isomers of dichloro-diammine-platinum

With a tetrahedral arrangement of ligands, cis-trans isomerism is impossible.

6. Mirror (optical) isomerism, for example, in the dichloro-diethylenediamino-chromium (III) + cation:

As in the case of organic substances, mirror isomers have the same physical and chemical properties and differ in the asymmetry of crystals and the direction of rotation of the light polarization plane.

7. Ligand isomerism , for example, for (NH 2) 2 (CH 2) 4 the following isomers are possible: (NH 2) - (CH 2) 4 -NH 2, CH 3 -NH-CH 2 -CH 2 -NH-CH 3, NH 2 -CH (CH 3) -CH 2 -CH 2 -NH 2

The problem of communication in complex compounds. The nature of the coupling in the CS is different, and three approaches are currently used for explanation: the VS method, the MO method, and the crystal field theory method.

Sun method Pauline introduced. The main provisions of the method:

1. A bond in a CS is formed as a result of a donor-acceptor interaction. The ligands provide electron pairs, while the complexing agent provides free orbitals. A measure of bond strength is the degree of orbital overlap.

2. CO orbitals undergo hybridization; the type of hybridization is determined by the number, nature, and electronic structure of the ligands. Hybridization of CO is determined by the geometry of the complex.

3. Additional strengthening of the complex occurs due to the fact that, along with the s-bond, a p-bond is formed.

4. The magnetic properties of the complex are determined by the number of unpaired electrons.

5. During the formation of a complex, the distribution of electrons in orbitals can remain both at neutral atoms and undergo changes. It depends on the nature of the ligands, its electrostatic field. A spectrochemical series of ligands has been developed. If the ligands have a strong field, then they displace the electrons, causing them to pair and form a new bond.

Spectrochemical series of ligands:

CN - >NO 2 - >NH 3 >CNS - >H 2 O>F - >OH - >Cl - >Br -

6. The VS method makes it possible to explain bond formation even in neutral and classter complexes

K 3 K 3

1. Ligands create a strong field in the first CS, and a weak field in the second

2. Draw the valence orbitals of iron:

3. Consider the donor properties of ligands: CN - have free electron orbitals and are donors of electron pairs.
Hosted on ref.rf
CN - has a strong field, acts on 3d orbitals, compacting them.

As a result, 6 bonds are formed, while the inner 3 dorbitals, ᴛ.ᴇ, participate in the connection. an intraorbital complex is formed. The complex is paramagnetic and low-spin, since there is one unpaired electron. The complex is stable, because occupied inner orbitals.

Ions F - have free electron orbitals and are donors of electron pairs, have a weak field, and therefore cannot condense electrons at the 3d level.

As a result, a paramagnetic, high-spin, outer-orbital complex is formed. Unstable and reactive.

Advantages of the VS method: informative

Disadvantages of the VS method: the method is suitable for a certain range of substances, the method does not explain the optical properties (colour), does not make an energy assessment, because in some cases a quadratic complex is formed instead of the more energetically favorable tetrahedral one.

complex compounds. - concept and types. Classification and features of the category "Complex compounds." 2017, 2018.

General chemistry: textbook / A. V. Zholnin; ed. V. A. Popkova, A. V. Zholnina. - 2012. - 400 p.: ill.

Chapter 7. COMPLEX COMPOUNDS

Chapter 7. COMPLEX COMPOUNDS

The complexing elements are the organizers of life.

K. B. Yatsimirsky

Complex compounds are the most extensive and diverse class of compounds. Living organisms contain complex compounds of biogenic metals with proteins, amino acids, porphyrins, nucleic acids, carbohydrates, and macrocyclic compounds. The most important processes of vital activity proceed with the participation of complex compounds. Some of them (hemoglobin, chlorophyll, hemocyanin, vitamin B 12, etc.) play a significant role in biochemical processes. Many drugs contain metal complexes. For example, insulin (zinc complex), vitamin B 12 (cobalt complex), platinol (platinum complex), etc.

7.1. COORDINATION THEORY OF A. WERNER

The structure of complex compounds

During the interaction of particles, mutual coordination of particles is observed, which can be defined as the process of complex formation. For example, the process of hydration of ions ends with the formation of aqua complexes. Complex formation reactions are accompanied by the transfer of electron pairs and lead to the formation or destruction of higher-order compounds, the so-called complex (coordination) compounds. A feature of complex compounds is the presence in them of a coordination bond that arose according to the donor-acceptor mechanism:

Complex compounds are compounds that exist both in the crystalline state and in solution.

which is the presence of a central atom surrounded by ligands. Complex compounds can be considered as complex compounds of a higher order, consisting of simple molecules capable of independent existence in solution.

According to Werner's coordination theory, in a complex compound, internal And outer sphere. The central atom with its surrounding ligands form the inner sphere of the complex. It is usually enclosed in square brackets. Everything else in a complex compound is the outer sphere and is written in square brackets. A certain number of ligands is placed around the central atom, which is determined coordination number(kch). The number of coordinated ligands is most often 6 or 4. The ligand occupies a coordination site near the central atom. Coordination changes the properties of both the ligands and the central atom. Often, coordinated ligands cannot be detected using chemical reactions characteristic of them in the free state. More tightly bound particles of the inner sphere are called complex (complex ion). Attraction forces act between the central atom and ligands (a covalent bond is formed according to the exchange and (or) donor-acceptor mechanism), and repulsive forces act between ligands. If the charge of the inner sphere is 0, then there is no outer coordination sphere.

Central atom (complexing agent)- an atom or ion that occupies a central position in a complex compound. The role of a complexing agent is most often performed by particles that have free orbits and a sufficiently large positive nuclear charge, and therefore can be electron acceptors. These are cations of transition elements. The strongest complexing agents are elements of groups IB and VIIIB. Rarely as a complex

neutral atoms of d-elements and non-metal atoms in various degrees of oxidation - . The number of free atomic orbitals provided by the complexing agent determines its coordination number. The value of the coordination number depends on many factors, but usually it is equal to twice the charge of the complexing ion:

Ligands- ions or molecules that are directly associated with the complexing agent and are donors of electron pairs. These electron-rich systems, which have free and mobile electron pairs, can be electron donors, for example:

Compounds of p-elements exhibit complexing properties and act as ligands in a complex compound. Ligands can be atoms and molecules (protein, amino acids, nucleic acids, carbohydrates). According to the number of bonds formed by ligands with the complexing agent, ligands are divided into mono-, di-, and polydentate ligands. The above ligands (molecules and anions) are monodentate, since they are donors of one electron pair. Bidentate ligands include molecules or ions containing two functional groups capable of being a donor of two electron pairs:

Polydentate ligands include the 6-dentate ligand of ethylenediaminetetraacetic acid:

The number of places occupied by each ligand in the inner sphere of the complex compound is called coordination capacity (denticity) of the ligand. It is determined by the number of electron pairs of the ligand that participate in the formation of a coordination bond with the central atom.

In addition to complex compounds, coordination chemistry covers double salts, crystalline hydrates, which decompose in an aqueous solution into constituent parts, which in the solid state in many cases are constructed similarly to complex ones, but are unstable.

The most stable and diverse complexes in terms of composition and the functions they perform form d-elements. Of particular importance are complex compounds of transition elements: iron, manganese, titanium, cobalt, copper, zinc and molybdenum. Biogenic s-elements (Na, K, Mg, Ca) form complex compounds only with ligands of a certain cyclic structure, also acting as a complexing agent. Main part R-elements (N, P, S, O) is the active active part of complexing particles (ligands), including bioligands. This is their biological significance.

Therefore, the ability to complex formation is a common property of the chemical elements of the periodic system, this ability decreases in the following order: f> d> p> s.

7.2. DETERMINATION OF THE CHARGE OF MAIN PARTICLES OF A COMPLEX COMPOUND

The charge of the inner sphere of a complex compound is the algebraic sum of the charges of its constituent particles. For example, the magnitude and sign of the charge of a complex are determined as follows. The charge of the aluminum ion is +3, the total charge of the six hydroxide ions is -6. Therefore, the charge of the complex is (+3) + (-6) = -3 and the formula of the complex is 3- . The charge of the complex ion is numerically equal to the total charge of the outer sphere and is opposite in sign to it. For example, the charge of the outer sphere K 3 is +3. Therefore, the charge of the complex ion is -3. The charge of the complexing agent is equal in magnitude and opposite in sign to the algebraic sum of the charges of all other particles of the complex compound. Hence, in K 3 the charge of the iron ion is +3, since the total charge of all other particles of the complex compound is (+3) + (-6) = -3.

7.3. NOMENCLATURE OF COMPLEX COMPOUNDS

The basics of nomenclature are developed in the classic works of Werner. In accordance with them, in a complex compound, the cation is first called, and then the anion. If the compound is of a non-electrolyte type, then it is called in one word. The name of the complex ion is written in one word.

The neutral ligand is named the same as the molecule, and an "o" is added to the anion ligands. For a coordinated water molecule, the designation "aqua-" is used. To indicate the number of identical ligands in the inner sphere of the complex, the Greek numerals di-, tri-, tetra-, penta-, hexa-, etc. are used as a prefix before the name of the ligands. The prefix monone is used. The ligands are listed in alphabetical order. The name of the ligand is considered as a single entity. After the name of the ligand, the name of the central atom follows, indicating the degree of oxidation, which is indicated by Roman numerals in parentheses. The word ammine (with two "m") is written in relation to ammonia. For all other amines, only one "m" is used.

C1 3 - hexamminecobalt (III) chloride.

C1 3 - aquapentamminecobalt (III) chloride.

Cl 2 - pentamethylamminechlorocobalt (III) chloride.

Diamminedibromoplatinum (II).

If the complex ion is an anion, then its Latin name has the ending "am".

(NH 4) 2 - ammonium tetrachloropalladate (II).

K - potassium pentabromoammineplatinate (IV).

K 2 - potassium tetrarodanocobaltate (II).

The name of a complex ligand is usually enclosed in parentheses.

NO 3 - dichloro-di-(ethylenediamine) cobalt (III) nitrate.

Br - bromo-tris-(triphenylphosphine) platinum (II) bromide.

In cases where the ligand binds two central ions, the Greek letter is used before its nameμ.

Such ligands are called bridge and listed last.

7.4. CHEMICAL BOND AND STRUCTURE OF COMPLEX COMPOUNDS

The donor-acceptor interactions between the ligand and the central atom play an important role in the formation of complex compounds. The electron pair donor is usually a ligand. An acceptor is a central atom that has free orbitals. This bond is strong and does not break when the complex is dissolved (nonionogenic), and it is called coordination.

Along with o-bonds, π-bonds are formed by the donor-acceptor mechanism. In this case, the metal ion serves as a donor, donating its paired d-electrons to the ligand, which has energetically favorable vacant orbitals. Such relationships are called dative. They are formed:

a) due to the overlap of the vacant p-orbitals of the metal with the d-orbital of the metal, on which there are electrons that have not entered into a σ-bond;

b) when the vacant d-orbitals of the ligand overlap with the filled d-orbitals of the metal.

A measure of its strength is the degree of overlap between the orbitals of the ligand and the central atom. The orientation of the bonds of the central atom determines the geometry of the complex. To explain the direction of bonds, the concept of hybridization of atomic orbitals of the central atom is used. Hybrid orbitals of the central atom are the result of mixing unequal atomic orbitals, as a result, the shape and energy of the orbitals change mutually, and orbitals of a new identical shape and energy are formed. The number of hybrid orbitals is always equal to the number of original ones. Hybrid clouds are located in the atom at the maximum distance from each other (Table 7.1).

Table 7.1. Types of hybridization of atomic orbitals of a complexing agent and the geometry of some complex compounds

The spatial structure of the complex is determined by the type of hybridization of valence orbitals and the number of unshared electron pairs contained in its valence energy level.

The efficiency of the donor-acceptor interaction between the ligand and the complexing agent, and, consequently, the strength of the bond between them (the stability of the complex) is determined by their polarizability, i.e. the ability to transform their electron shells under external influence. On this basis, the reagents are divided into "hard" or low polarizable, and "soft" - easily polarizable. The polarity of an atom, molecule or ion depends on their size and the number of electron layers. The smaller the radius and electrons of a particle, the less polarized it is. The smaller the radius and the fewer electrons a particle has, the worse it polarizes.

Hard acids form strong (hard) complexes with electronegative O, N, F atoms of ligands (hard bases), while soft acids form strong (soft) complexes with donor P, S, and I atoms of ligands having low electronegativity and high polarizability. We observe here the manifestation of the general principle "like with like".

Due to their rigidity, sodium and potassium ions practically do not form stable complexes with biosubstrates and are found in physiological media in the form of aquacomplexes. Ions Ca 2 + and Mg 2 + form quite stable complexes with proteins and therefore in physiological media are in both ionic and bound states.

Ions of d-elements form strong complexes with biosubstrates (proteins). And soft acids Cd, Pb, Hg are highly toxic. They form strong complexes with proteins containing R-SH sulfhydryl groups:

The cyanide ion is toxic. The soft ligand actively interacts with d-metals in complexes with biosubstrates, activating the latter.

7.5. DISSOCIATION OF COMPLEX COMPOUNDS. STABILITY OF COMPLEXES. LABILE AND INERT COMPLEXES

When complex compounds are dissolved in water, they usually decompose into ions of the outer and inner spheres, like strong electrolytes, since these ions are bound ionogenically, mainly by electrostatic forces. This is estimated as the primary dissociation of complex compounds.

The secondary dissociation of a complex compound is the disintegration of the inner sphere into its constituent components. This process proceeds according to the type of weak electrolytes, since the particles of the inner sphere are connected nonionically (covalently). Dissociation has a stepwise character:

For a qualitative characteristic of the stability of the inner sphere of a complex compound, an equilibrium constant is used that describes its complete dissociation, called complex instability constant(Kn). For a complex anion, the expression for the instability constant has the form:

The smaller the value of Kn, the more stable is the inner sphere of the complex compound, i.e. the less it dissociates in aqueous solution. Recently, instead of Kn, the value of the stability constant (Ku) is used - the reciprocal of Kn. The larger the Ku value, the more stable the complex.

The stability constants make it possible to predict the direction of ligand exchange processes.

In an aqueous solution, the metal ion exists in the form of aqua complexes: 2+ - hexaaqua iron (II), 2 + - tetraaqua copper (II). When writing formulas for hydrated ions, the coordinated water molecules of the hydration shell are not indicated, but implied. The formation of a complex between a metal ion and some ligand is considered as a reaction of substitution of a water molecule in the inner coordination sphere by this ligand.

Ligand exchange reactions proceed according to the mechanism of S N -type reactions. For example:

The values ​​of the stability constants given in Table 7.2 indicate that due to the complex formation process, strong binding of ions in aqueous solutions occurs, which indicates the effectiveness of using this type of reaction for binding ions, especially with polydentate ligands.

Table 7.2. Stability of zirconium complexes

Unlike ion exchange reactions, the formation of complex compounds is often not a quasi-instantaneous process. For example, when iron (III) reacts with nitrile trimethylenephosphonic acid, the equilibrium is established after 4 days. For the kinetic characteristics of complexes, the concepts are used - labile(fast reacting) and inert(slowly reacting). According to the suggestion of G. Taube, labile complexes are considered to be those that completely exchange ligands for 1 min at room temperature and a solution concentration of 0.1 M. It is necessary to clearly distinguish between thermodynamic concepts [strong (stable) / fragile (unstable)] and kinetic [ inert and labile] complexes.

In labile complexes, ligand substitution occurs rapidly and equilibrium is quickly established. In inert complexes, ligand substitution proceeds slowly.

So, the inert complex 2 + in an acidic environment is thermodynamically unstable: the instability constant is 10 -6, and the labile complex 2- is very stable: the stability constant is 10 -30. Taube associates the lability of complexes with the electronic structure of the central atom. The inertness of complexes is characteristic mainly of ions with an incomplete d-shell. Inert complexes include Co, Cr. Cyanide complexes of many cations with an external level of s 2 p 6 are labile.

7.6. CHEMICAL PROPERTIES OF COMPLEXES

The processes of complex formation affect practically the properties of all particles forming the complex. The higher the strength of the bonds between the ligand and the complexing agent, the less the properties of the central atom and ligands manifest themselves in the solution, and the more pronounced the features of the complex.

Complex compounds exhibit chemical and biological activity as a result of the coordination unsaturation of the central atom (there are free orbitals) and the presence of free electron pairs of ligands. In this case, the complex has electrophilic and nucleophilic properties that differ from those of the central atom and ligands.

It is necessary to take into account the influence on the chemical and biological activity of the structure of the hydration shell of the complex. The process of education

The reduction of complexes affects the acid-base properties of the complex compound. The formation of complex acids is accompanied by an increase in the strength of the acid or base, respectively. So, when complex acids are formed from simple ones, the binding energy with H + ions decreases and the strength of the acid increases accordingly. If there is an OH - ion in the outer sphere, then the bond between the complex cation and the hydroxide ion of the outer sphere decreases, and the basic properties of the complex increase. For example, copper hydroxide Cu (OH) 2 is a weak, sparingly soluble base. Under the action of ammonia on it, copper ammonia (OH) 2 is formed. The charge density of 2 + decreases compared to Cu 2 +, the bond with OH - ions is weakened, and (OH) 2 behaves like a strong base. The acid-base properties of the ligands associated with the complexing agent are usually more pronounced than the acid-base properties of them in the free state. For example, hemoglobin (Hb) or oxyhemoglobin (HbO 2) exhibit acidic properties due to the free carboxyl groups of the globin protein, which is a ligand of HHb ↔ H + + Hb - . At the same time, the hemoglobin anion, due to the amino groups of the globin protein, exhibits basic properties and therefore binds the acidic CO 2 oxide to form the carbaminohemoglobin anion (HbCO 2 -): CO 2 + Hb - ↔ HbCO 2 - .

The complexes exhibit redox properties due to redox transformations of the complexing agent, which forms stable oxidation states. The process of complexation strongly affects the values ​​of the reduction potentials of d-elements. If the reduced form of the cations forms a more stable complex with the given ligand than its oxidized form, then the value of the potential increases. A decrease in the potential value occurs when the oxidized form forms a more stable complex. For example, under the action of oxidizing agents: nitrites, nitrates, NO 2 , H 2 O 2, hemoglobin is converted into methemoglobin as a result of oxidation of the central atom.

The sixth orbital is used in the formation of oxyhemoglobin. The same orbital is involved in the formation of a bond with carbon monoxide. As a result, a macrocyclic complex with iron is formed - carboxyhemoglobin. This complex is 200 times more stable than the iron-oxygen complex in heme.

Rice. 7.1. Chemical transformations of hemoglobin in the human body. Scheme from the book: Slesarev V.I. Fundamentals of Living Chemistry, 2000

The formation of complex ions affects the catalytic activity of complexing ions. In some cases, activity is increasing. This is due to the formation in solution of large structural systems that can participate in the creation of intermediate products and a decrease in the activation energy of the reaction. For example, if Cu 2+ or NH 3 is added to H 2 O 2, the decomposition process is not accelerated. In the presence of the 2+ complex, which is formed in an alkaline medium, the decomposition of hydrogen peroxide is accelerated by 40 million times.

So, on hemoglobin, one can consider the properties of complex compounds: acid-base, complex formation and redox.

7.7. CLASSIFICATION OF COMPLEX COMPOUNDS

There are several classification systems for complex compounds based on different principles.

1. According to the belonging of a complex compound to a certain class of compounds:

Complex acids H 2 ;

Complex bases OH;

Complex salts K 4 .

2. By the nature of the ligand: aqua complexes, ammoniates, acido complexes (anions of various acids, K 4, act as ligands; hydroxo complexes (hydroxyl groups, K 3, as ligands); complexes with macrocyclic ligands, inside which central atom.

3. By the sign of the charge of the complex: cationic - complex cation in the complex compound Cl 3; anionic - a complex anion in a complex compound K; neutral - the charge of the complex is 0. The complex compound of the outer sphere does not have, for example, . This is the formula for an anticancer drug.

4. According to the internal structure of the complex:

a) depending on the number of atoms of the complexing agent: mononuclear- the composition of the complex particle includes one atom of the complexing agent, for example Cl 3 ; multi-core- in the composition of the complex particle there are several atoms of the complexing agent - an iron-protein complex:

b) depending on the number of types of ligands, complexes are distinguished: homogeneous (single-ligand), containing one type of ligand, for example 2+, and heterogeneous (multi-ligand)- two kinds of ligands or more, for example Pt(NH 3) 2 Cl 2 . The complex includes NH 3 and Cl - ligands. For complex compounds containing different ligands in the inner sphere, geometric isomerism is characteristic, when, with the same composition of the inner sphere, the ligands in it are located differently relative to each other.

Geometric isomers of complex compounds differ not only in physical and chemical properties, but also in biological activity. The cis-isomer of Pt(NH 3) 2 Cl 2 has a pronounced antitumor activity, while the trans-isomer does not;

c) depending on the denticity of the ligands forming mononuclear complexes, the following groups can be distinguished:

Mononuclear complexes with monodentate ligands, for example 3+ ;

Mononuclear complexes with polydentate ligands. Complex compounds with polydentate ligands are called chelating compounds;

d) cyclic and acyclic forms of complex compounds.

7.8. CHELATE COMPLEXES. COMPLEXSONS. COMPLEXONATES

Cyclic structures that are formed as a result of the addition of a metal ion to two or more donor atoms belonging to one chelating agent molecule are called chelate compounds. For example, copper glycinate:

In them, the complexing agent, as it were, leads inside the ligand, is covered by bonds, like claws, therefore, other things being equal, they are more stable than compounds that do not contain cycles. The most stable are cycles consisting of five or six links. This rule was first formulated by L.A. Chugaev. Difference

stability of the chelate complex and the stability of its non-cyclic analogue are called chelate effect.

Polydentate ligands that contain 2 types of groups act as a chelating agent:

1) groups capable of forming covalent polar bonds due to exchange reactions (proton donors, electron pair acceptors) -CH 2 COOH, -CH 2 PO (OH) 2, -CH 2 SO 2 OH, - acid groups (centers);

2) electron pair donor groups: ≡N, >NH, >C=O, -S-, -OH, - main groups (centers).

If such ligands saturate the inner coordination sphere of the complex and completely neutralize the charge of the metal ion, then the compounds are called intracomplex. For example, copper glycinate. There is no outer sphere in this complex.

A large group of organic substances containing basic and acid centers in the molecule is called complexones. These are polybasic acids. Chelate compounds formed by complexones when interacting with metal ions are called complexonates, for example, magnesium complexonate with ethylenediaminetetraacetic acid:

In aqueous solution, the complex exists in the anionic form.

Complexons and complexonates are a simple model of more complex compounds of living organisms: amino acids, polypeptides, proteins, nucleic acids, enzymes, vitamins and many other endogenous compounds.

Currently, a huge range of synthetic complexones with various functional groups is being produced. The formulas of the main complexones are presented below:

Complexons, under certain conditions, can provide unshared electron pairs (several) for the formation of a coordination bond with a metal ion (s-, p- or d-element). As a result, stable chelate-type compounds with 4-, 5-, 6-, or 8-membered rings are formed. The reaction proceeds over a wide pH range. Depending on pH, the nature of the complexing agent, its ratio with the ligand, complexonates of various strengths and solubility are formed. The chemistry of the formation of complexonates can be represented by equations using the sodium salt of EDTA (Na 2 H 2 Y) as an example, which dissociates in an aqueous solution: Na 2 H 2 Y→ 2Na + + H 2 Y 2-, and the H 2 Y 2- ion interacts with ions metals, regardless of the degree of oxidation of the metal cation, most often one metal ion (1:1) interacts with one complexone molecule. The reaction proceeds quantitatively (Kp>10 9).

Complexones and complexonates exhibit amphoteric properties in a wide pH range, the ability to participate in oxidation-reduction reactions, complex formation, form compounds with various properties depending on the degree of oxidation of the metal, its coordination saturation, and have electrophilic and nucleophilic properties. All this determines the ability to bind a huge number of particles, which allows a small amount of reagent to solve large and diverse problems.

Another indisputable advantage of complexones and complexonates is their low toxicity and the ability to convert toxic particles

into low-toxic or even biologically active ones. Decomposition products of complexonates do not accumulate in the body and are harmless. The third feature of complexonates is the possibility of their use as a source of trace elements.

Increased digestibility is due to the fact that the trace element is introduced in a biologically active form and has a high membrane permeability.

7.9. PHOSPHORUS-CONTAINING METAL COMPLEXONATES - AN EFFECTIVE FORM OF TRANSFORMATION OF MICRO AND MACRO ELEMENTS INTO A BIOLOGICALLY ACTIVE STATE AND A MODEL FOR STUDYING THE BIOLOGICAL ACTION OF CHEMICAL ELEMENTS

concept biological activity covers a wide range of phenomena. From the point of view of chemical action, biologically active substances (BAS) are commonly understood as substances that can act on biological systems, regulating their vital activity.

The ability to such an impact is interpreted as the ability to exhibit biological activity. Regulation can manifest itself in the effects of stimulation, oppression, development of certain effects. The extreme manifestation of biological activity is biocidal action, when, as a result of the action of a biocide substance on the body, the latter dies. At lower concentrations, in most cases, biocides have a stimulating rather than lethal effect on living organisms.

A large number of such substances are currently known. Nevertheless, in many cases, the use of known biologically active substances is used insufficiently, often with efficiency far from maximum, and the use often leads to side effects that can be eliminated by introducing modifiers into biologically active substances.

Phosphorus-containing complexonates form compounds with various properties depending on the nature, degree of oxidation of the metal, coordination saturation, composition and structure of the hydrate shell. All this determines the multifunctionality of complexonates, their unique ability of substoichiometric action,

the effect of a common ion and provides wide application in medicine, biology, ecology and in various sectors of the national economy.

When the metal ion coordinates the complexon, the electron density is redistributed. Due to the participation of a lone electron pair in the donor-acceptor interaction, the electron density of the ligand (complexon) shifts to the central atom. A decrease in the relatively negative charge on the ligand contributes to a decrease in the Coulomb repulsion of the reagents. Therefore, the coordinated ligand becomes more accessible to attack by a nucleophilic reagent that has an excess of electron density on the reaction center. The shift of the electron density from the complexing agent to the metal ion leads to a relative increase in the positive charge of the carbon atom, and, consequently, to the facilitation of its attack by the nucleophilic reagent, the hydroxyl ion. Among the enzymes that catalyze metabolic processes in biological systems, the hydroxylated complex occupies one of the central places in the mechanism of enzymatic action and detoxification of the body. As a result of the multipoint interaction of the enzyme with the substrate, orientation occurs, which ensures the convergence of active groups in the active center and the transfer of the reaction to the intramolecular regime, before the reaction begins and the transition state is formed, which ensures the enzymatic function of FCM. Conformational changes can occur in enzyme molecules. Coordination creates additional conditions for the redox interaction between the central ion and the ligand, since a direct bond is established between the oxidizing agent and the reducing agent, which ensures the transfer of electrons. FCM transition metal complexes can be characterized by L-M, M-L, M-L-M type electron transitions, in which the orbitals of both the metal (M) and ligands (L) participate, which are respectively linked in the complex by donor-acceptor bonds. Complexons can serve as a bridge along which the electrons of multinuclear complexes oscillate between the central atoms of one or different elements in different oxidation states. (electron and proton transport complexes). Complexons determine the reducing properties of metal complexonates, which allows them to exhibit high antioxidant, adaptogenic properties, homeostatic functions.

So, complexones convert microelements into a biologically active, accessible form for the body. They form stable

more coordinatively saturated particles, incapable of destroying biocomplexes, and, consequently, low-toxic forms. Complexonates favorably act in violation of the microelement homeostasis of the body. Ions of transition elements in the complexonate form act in the body as a factor that determines the high sensitivity of cells to microelements through their participation in the creation of a high concentration gradient, the membrane potential. Transition metal complexonates FKM have bioregulatory properties.

The presence of acidic and basic centers in the composition of FCM provides amphoteric properties and their participation in maintaining acid-base balance (isohydric state).

With an increase in the number of phosphonic groups in the composition of the complexone, the composition and conditions for the formation of soluble and poorly soluble complexes change. An increase in the number of phosphonic groups favors the formation of sparingly soluble complexes in a wider pH range and shifts the area of ​​their existence to the acidic area. The decomposition of the complexes occurs at a pH of more than 9.

The study of the processes of complex formation with complexones made it possible to develop methods for the synthesis of bioregulators:

Growth stimulants of prolonged action in a colloid-chemical form are polynuclear homo- and heterocomplex compounds of titanium and iron;

Growth stimulants in water-soluble form. These are mixed-ligand titanium complexonates based on complexones and an inorganic ligand;

Growth inhibitors - phosphorus-containing complexonates of s-elements.

The biological effect of the synthesized preparations on growth and development was studied in a chronic experiment on plants, animals and humans.

Bioregulation- this is a new scientific direction that allows you to regulate the direction and intensity of biochemical processes, which can be widely used in medicine, animal husbandry and crop production. It is associated with the development of ways to restore the physiological function of the body in order to prevent and treat diseases and age-related pathologies. Complexones and complex compounds based on them can be classified as promising biologically active compounds. The study of their biological action in a chronic experiment showed that chemistry gave into the hands of physicians,

livestock breeders, agronomists and biologists, a new promising tool that allows you to actively influence a living cell, regulate nutritional conditions, growth and development of living organisms.

A study of the toxicity of the complexones and complexonates used showed the complete absence of the effect of drugs on the hematopoietic organs, blood pressure, excitability, respiratory rate: no change in liver function was noted, no toxicological effect on the morphology of tissues and organs was detected. Potassium salt of HEDP has no toxicity at a dose 5-10 times higher than the therapeutic one (10-20 mg/kg) in the study for 181 days. Therefore, complexones are classified as low-toxic compounds. They are used as medicines to combat viral diseases, poisoning with heavy metals and radioactive elements, calcium metabolism disorders, endemic diseases and microelement imbalance in the body. Phosphorus-containing complexons and complexonates do not undergo photolysis.

Progressive pollution of the environment with heavy metals - products of human economic activity is a permanent environmental factor. They can accumulate in the body. Excess and lack of them cause intoxication of the body.

Metal complexonates retain the chelating effect on the ligand (complexone) in the body and are indispensable for maintaining metal ligand homeostasis. Incorporated heavy metals are neutralized to a certain extent in the body, and low resorption capacity prevents the transfer of metals along trophic chains, as a result, this leads to a certain "biominization" of their toxic effect, which is especially important for the Ural region. For example, the free lead ion belongs to thiol poisons, and the strong complexonate of lead with ethylenediaminetetraacetic acid is of low toxicity. Therefore, detoxification of plants and animals consists in the use of metal complexonates. It is based on two thermodynamic principles: their ability to form strong bonds with toxic particles, turning them into poorly soluble or stable compounds in an aqueous solution; their inability to destroy endogenous biocomplexes. In this regard, we consider an important direction in the fight against eco-poisoning and obtaining environmentally friendly products - this is complex therapy of plants and animals.

A study was made of the effect of plant treatment with complexonates of various metals under intensive cultivation technology.

potatoes on the microelement composition of potato tubers. Tuber samples contained 105-116 mg/kg iron, 16-20 mg/kg manganese, 13-18 mg/kg copper and 11-15 mg/kg zinc. The ratio and content of microelements are typical for plant tissues. Tubers grown with and without the use of metal complexonates have almost the same elemental composition. The use of chelates does not create conditions for the accumulation of heavy metals in tubers. Complexonates, to a lesser extent than metal ions, are sorbed by the soil, are resistant to its microbiological effects, which allows them to be retained in the soil solution for a long time. The aftereffect is 3-4 years. They combine well with various pesticides. The metal in the complex has a lower toxicity. Phosphorus-containing metal complexonates do not irritate the mucous membrane of the eyes and do not damage the skin. Sensitizing properties have not been identified, the cumulative properties of titanium complexonates are not pronounced, and in some cases they are very weakly expressed. The cumulation coefficient is 0.9-3.0, which indicates a low potential danger of chronic drug poisoning.

Phosphorus-containing complexes are based on the phosphorus-carbon bond (C-P), which is also found in biological systems. It is part of the phosphonolipids, phosphonoglycans and phosphoproteins of cell membranes. Lipids containing aminophosphonic compounds are resistant to enzymatic hydrolysis, provide stability and, consequently, normal functioning of the outer cell membranes. Synthetic analogues of pyrophosphates - diphosphonates (Р-С-Р) or (Р-С-С-Р) in large doses disrupt calcium metabolism, and in small doses normalize it. Diphosphonates are effective in hyperlipemia and promising from the standpoint of pharmacology.

Diphosphonates containing P-C-P bonds are structural elements of biosystems. They are biologically effective and are analogues of pyrophosphates. Diphosphonates have been shown to be effective in the treatment of various diseases. Diphosphonates are active inhibitors of bone mineralization and resorption. Complexons convert microelements into a biologically active, accessible form for the body, form stable, more coordinatively saturated particles that are unable to destroy biocomplexes, and therefore, low-toxic forms. They determine the high sensitivity of cells to trace elements, participating in the formation of a high concentration gradient. Able to participate in the formation of polynuclear titanium compounds

of a different type - electron and proton transport complexes, participate in the bioregulation of metabolic processes, body resistance, the ability to form bonds with toxic particles, turning them into poorly soluble or soluble, stable, non-destructive endogenous complexes. Therefore, their use for detoxification, elimination from the body, obtaining environmentally friendly products (complex therapy), as well as in industry for the regeneration and disposal of industrial wastes of inorganic acids and transition metal salts is very promising.

7.10. LIGAND EXCHANGE AND METAL EXCHANGE

BALANCE. CHELATHERAPY

If there are several ligands with one metal ion or several metal ions with one ligand capable of forming complex compounds in the system, then competing processes are observed: in the first case, ligand-exchange equilibrium is competition between ligands for a metal ion, in the second case, metal-exchange equilibrium is competition between ions metal for the ligand. The process of formation of the most durable complex will prevail. For example, in solution there are ions: magnesium, zinc, iron (III), copper, chromium (II), iron (II) and manganese (II). When a small amount of ethylenediaminetetraacetic acid (EDTA) is introduced into this solution, competition between metal ions and binding to the iron (III) complex occur, since it forms the most stable complex with EDTA.

Interaction of biometals (Mb) and bioligands (Lb), formation and destruction of vital biocomplexes (MbLb) are constantly taking place in the body:

In the body of humans, animals and plants, there are various mechanisms for protecting and maintaining this balance from various xenobiotics (foreign substances), including heavy metal ions. Ions of heavy metals that are not bound into a complex and their hydroxo complexes are toxic particles (Mt). In these cases, along with the natural metal ligand equilibrium, a new equilibrium may arise, with the formation of more stable foreign complexes containing toxicant metals (MtLb) or toxicant ligands (MbLt), which do not fulfill

essential biological functions. When exogenous toxic particles enter the body, combined equilibria arise and, as a result, competition of processes occurs. The predominant process will be the one that leads to the formation of the most stable complex compound:

Violations of metal ligand homeostasis cause metabolic disorders, inhibit the activity of enzymes, destroy important metabolites such as ATP, cell membranes, and disrupt the ion concentration gradient in cells. Therefore, artificial protection systems are being created. Chelation therapy (complex therapy) takes its due place in this method.

Chelation therapy is the removal of toxic particles from the body, based on their chelation with s-element complexonates. Drugs used to remove toxic particles incorporated in the body are called detoxifiers.(Lg). Chelation of toxic species with metal complexonates (Lg) converts toxic metal ions (Mt) into non-toxic (MtLg) bound forms suitable for isolation and membrane penetration, transport and excretion from the body. They retain a chelating effect in the body both for the ligand (complexon) and for the metal ion. This ensures the metal ligand homeostasis of the body. Therefore, the use of complexonates in medicine, animal husbandry, and crop production provides detoxification of the body.

The basic thermodynamic principles of chelation therapy can be formulated in two positions.

I. A detoxicant (Lg) must effectively bind toxicant ions (Mt, Lt), newly formed compounds (MtLg) must be stronger than those that existed in the body:

II. The detoxifier should not destroy vital complex compounds (MbLb); compounds that can be formed during the interaction of a detoxifier and biometal ions (MbLg) should be less strong than those existing in the body:

7.11. APPLICATION OF COMPLEXONS AND COMPLEXONATES IN MEDICINE

Complexone molecules practically do not undergo splitting or any change in the biological environment, which is their important pharmacological feature. Complexons are insoluble in lipids and highly soluble in water, so they do not penetrate or penetrate poorly through cell membranes, and therefore: 1) are not excreted by the intestines; 2) the absorption of complexing agents occurs only when they are injected (only penicillamine is taken orally); 3) in the body, complexons circulate mainly in the extracellular space; 4) excretion from the body is carried out mainly through the kidneys. This process is fast.

Substances that eliminate the effects of poisons on biological structures and inactivate poisons through chemical reactions are called antidotes.

One of the first antidotes to be used in chelation therapy is British Anti-Lewisite (BAL). Unithiol is currently used:

This drug effectively removes arsenic, mercury, chromium and bismuth from the body. The most widely used for poisoning with zinc, cadmium, lead and mercury are complexones and complexonates. Their use is based on the formation of stronger complexes with metal ions than complexes of the same ions with sulfur-containing groups of proteins, amino acids and carbohydrates. EDTA preparations are used to remove lead. The introduction of large doses of drugs into the body is dangerous, since they bind calcium ions, which leads to disruption of many functions. Therefore, apply tetacin(CaNa 2 EDTA), which is used to remove lead, cadmium, mercury, yttrium, cerium and other rare earth metals and cobalt.

Since the first therapeutic use of tetacin in 1952, this drug has found wide use in the clinic of occupational diseases and continues to be an indispensable antidote. The mechanism of action of tetacin is very interesting. Ions-toxicants displace the coordinated calcium ion from tetacin due to the formation of stronger bonds with oxygen and EDTA. The calcium ion, in turn, displaces the two remaining sodium ions:

Tetacin is introduced into the body in the form of a 5-10% solution, the basis of which is saline. So, already 1.5 hours after intraperitoneal injection, 15% of the administered dose of tetacin remains in the body, after 6 hours - 3%, and after 2 days - only 0.5%. The drug acts effectively and quickly when using the inhalation method of tetacin administration. It is rapidly absorbed and circulates in the blood for a long time. In addition, tetacin is used in protection against gas gangrene. It inhibits the action of zinc and cobalt ions, which are activators of the enzyme lecithinase, which is a gas gangrene toxin.

The binding of toxicants with tetacin into a low-toxic and more durable chelate complex, which is not destroyed and is easily excreted from the body through the kidneys, provides detoxification and balanced mineral nutrition. Close in structure and composition to pre-

paratam EDTA is the sodium-calcium salt of diethylenetriamine-pentaacetic acid (CaNa 3 DTPA) - pentacin and sodium salt of dacid (Na 6 DTPF) - trimefacin. Pentacin is used mainly for poisoning with iron, cadmium and lead compounds, as well as for the removal of radionuclides (technetium, plutonium, uranium).

Sodium salt of ethyacid (СаNa 2 EDTP) phosphicin successfully used to remove mercury, lead, beryllium, manganese, actinides and other metals from the body. Complexonates are very effective in removing some toxic anions. For example, cobalt (II) ethylenediaminetetraacetate, which forms a mixed-ligand complex with CN - , can be recommended as an antidote for cyanide poisoning. A similar principle underlies methods for removing toxic organic substances, including pesticides containing functional groups with donor atoms capable of interacting with the complexonate metal.

An effective drug is succimer(dimercaptosuccinic acid, dimercaptosuccinic acid, chemet). It strongly binds almost all toxicants (Hg, As, Pb, Cd), but removes ions of biogenic elements (Cu, Fe, Zn, Co) from the body, so it is almost never used.

Phosphorus-containing complexonates are powerful inhibitors of crystal formation of phosphates and calcium oxalates. As an anticalcifying drug in the treatment of urolithiasis, ksidifon, a potassium-sodium salt of OEDP, is proposed. Diphosphonates, in addition, in minimal doses increase the incorporation of calcium into bone tissue, and prevent its pathological exit from the bones. HEDP and other diphosphonates prevent various types of osteoporosis, including renal osteodystrophy, periodontal

ny destruction, as well as the destruction of the transplanted bone in animals. The anti-atherosclerotic effect of HEDP has also been described.

In the USA, a number of diphosphonates, in particular HEDP, have been proposed as pharmaceutical preparations for the treatment of humans and animals suffering from metastasized bone cancer. By regulating membrane permeability, bisphosphonates promote the transport of antitumor drugs into the cell, and hence the effective treatment of various oncological diseases.

One of the urgent problems of modern medicine is the task of rapid diagnosis of various diseases. In this aspect, of undoubted interest is a new class of preparations containing cations capable of performing the functions of a probe - radioactive magnetorelaxation and fluorescent labels. Radioisotopes of certain metals are used as the main components of radiopharmaceuticals. Chelation of the cations of these isotopes with complexones makes it possible to increase their toxicological acceptability for the body, to facilitate their transportation, and to ensure, within certain limits, the selectivity of concentration in certain organs.

These examples by no means exhaust the whole variety of forms of application of complexonates in medicine. Thus, the dipotassium salt of magnesium ethylenediaminetetraacetate is used to regulate the fluid content in tissues in pathology. EDTA is used in the composition of anticoagulant suspensions used in the separation of blood plasma, as a stabilizer of adenosine triphosphate in the determination of blood glucose, in the clarification and storage of contact lenses. Diphosphonates are widely used in the treatment of rheumatoid diseases. They are especially effective as anti-arthritic agents in combination with anti-inflammatory agents.

7.12. COMPLEXES WITH MACROCYCLIC COMPOUNDS

Among natural complex compounds, a special place is occupied by macrocomplexes based on cyclic polypeptides containing internal cavities of certain sizes, in which there are several oxygen-containing groups capable of binding cations of those metals, including sodium and potassium, whose dimensions correspond to the dimensions of the cavity. Such substances, being in biological

Rice. 7.2. Complex of valinomycin with K+ ion

ical materials, provide transport of ions through membranes and are therefore called ionophores. For example, valinomycin transports a potassium ion across the membrane (Fig. 7.2).

With the help of another polypeptide - gramicidin A sodium cations are transported by the relay mechanism. This polypeptide is folded into a "tube", the inner surface of which is lined with oxygen-containing groups. The result is

a sufficiently long hydrophilic channel with a certain cross section corresponding to the size of the sodium ion. The sodium ion, entering the hydrophilic channel from one side, is transferred from one to the other oxygen groups, like a relay race through an ion-conducting channel.

Thus, a cyclic polypeptide molecule has an intramolecular cavity, into which a substrate of a certain size and geometry can enter according to the principle of a key and a lock. The cavity of such internal receptors is lined with active centers (endoreceptors). Depending on the nature of the metal ion, non-covalent interaction (electrostatic, hydrogen bonding, van der Waals forces) with alkali metals and covalent interaction with alkaline earth metals can occur. As a result of this, supramolecules- complex associates consisting of two or more particles held together by intermolecular forces.

The most common in living nature are tetradentate macrocycles - porphins and corrinoids close to them in structure. Schematically, the tetradent cycle can be represented in the following form (Fig. 7.3), where the arcs mean the same type of carbon chains connecting donor nitrogen atoms in a closed cycle; R 1 , R 2 , R 3 , P 4 are hydrocarbon radicals; M n+ - metal ion: in chlorophyll Mg 2+ ion, in hemoglobin Fe 2+ ion, in hemocyanin Cu 2+ ion, in vitamin B 12 (cobalamin) Co 3+ ion.

Donor nitrogen atoms are located at the corners of the square (indicated by the dotted line). They are tightly coordinated in space. That's why

porphyrins and corrinoids form strong complexes with cations of various elements and even alkaline earth metals. It is significant that Regardless of the denticity of the ligand, the chemical bond and structure of the complex are determined by donor atoms. For example, copper complexes with NH 3 , ethylenediamine, and porphyrin have the same square structure and a similar electronic configuration. But polydentate ligands bind to metal ions much more strongly than monodentate ligands.

Rice. 7.3. Tetradentate macrocycle

with the same donor atoms. The strength of ethylenediamine complexes is 8-10 orders of magnitude greater than the strength of the same metals with ammonia.

Bioinorganic complexes of metal ions with proteins are called bioclusters - complexes of metal ions with macrocyclic compounds (Fig. 7.4).

Rice. 7.4. Schematic representation of the structure of bioclusters of certain sizes of protein complexes with ions of d-elements. Types of interactions of a protein molecule. M n+ - active center metal ion

There is a cavity inside the biocluster. It includes a metal that interacts with donor atoms of the linking groups: OH - , SH - , COO - , -NH 2 , proteins, amino acids. The most famous metal-

ments (carbonic anhydrase, xanthine oxidase, cytochromes) are bioclusters whose cavities form enzyme centers containing Zn, Mo, Fe, respectively.

7.13. MULTICORE COMPLEXES

Heterovalent and heteronuclear complexes

Complexes, which include several central atoms of one or different elements, are called multi-core. The possibility of forming multinuclear complexes is determined by the ability of some ligands to bind to two or three metal ions. Such ligands are called bridge. Respectively bridge are called complexes. In principle, one-atom bridges are also possible, for example:

They use lone electron pairs belonging to the same atom. The role of bridges can be played polyatomic ligands. In such bridges, unshared electron pairs belonging to different atoms are used. polyatomic ligand.

A.A. Grinberg and F.M. Filinov studied bridging compounds of composition , in which the ligand binds complex compounds of the same metal, but in different oxidation states. G. Taube called them electron transfer complexes. He investigated the reactions of electron transfer between the central atoms of various metals. Systematic studies of the kinetics and mechanism of redox reactions have led to the conclusion that the transfer of an electron between two complexes is

proceeds through the resulting ligand bridge. The exchange of an electron between 2 + and 2 + occurs through the formation of an intermediate bridge complex (Fig. 7.5). Electron transfer occurs through the chloride bridging ligand, ending in the formation of 2+ complexes; 2+.

Rice. 7.5. Electron transfer in an intermediate multinuclear complex

A wide variety of polynuclear complexes has been obtained through the use of organic ligands containing several donor groups. The condition for their formation is such an arrangement of donor groups in the ligand that does not allow chelate cycles to close. It is not uncommon for a ligand to close the chelate cycle and simultaneously act as a bridge.

The active principle of electron transfer are transition metals that exhibit several stable oxidation states. This gives titanium, iron and copper ions ideal electron carrier properties. The set of options for the formation of heterovalent (HVA) and heteronuclear complexes (HNC) based on Ti and Fe is shown in Fig. 3. 7.6.

reaction

Reaction (1) is called cross reaction. In exchange reactions, the intermediate will be heterovalent complexes. All theoretically possible complexes are actually formed in solution under certain conditions, which is proved by various physicochemical studies.

Rice. 7.6. Formation of heterovalent complexes and heteronuclear complexes containing Ti and Fe

methods. For electron transfer to occur, the reactants must be in states close in energy. This requirement is called the Franck-Condon principle. Electron transfer can occur between atoms of the same transition element, which are in different degrees of HWC oxidation, or different HJC elements, the nature of metal centers of which is different. These compounds can be defined as electron transport complexes. They are convenient carriers of electrons and protons in biological systems. The addition and release of an electron causes changes only in the electronic configuration of the metal, without changing the structure of the organic component of the complex. All these elements have several stable oxidation states (Ti +3 and +4; Fe +2 and +3; Cu +1 and +2). In our opinion, these systems are given by nature a unique role of ensuring the reversibility of biochemical processes with minimal energy costs. Reversible reactions include reactions that have thermodynamic and thermochemical constants from 10 -3 to 10 3 and with a small value of ΔG o and E o processes. Under these conditions, the initial substances and reaction products can be in comparable concentrations. When changing them in a certain range, it is easy to achieve the reversibility of the process, therefore, in biological systems, many processes are oscillatory (wave) in nature. Redox systems containing the above pairs cover a wide range of potentials, which allows them to enter into interactions accompanied by moderate changes in Δ Go And E°, with many substrates.

The probability of formation of HVA and HJA increases significantly when the solution contains potentially bridging ligands, i.e. molecules or ions (amino acids, hydroxy acids, complexones, etc.) capable of linking two metal centers at once. The possibility of delocalization of an electron in the HWC contributes to a decrease in the total energy of the complex.

More realistically, the set of possible options for the formation of HWC and HJA, in which the nature of the metal centers is different, is seen in Fig. 7.6. A detailed description of the formation of HVA and HNA and their role in biochemical systems are considered in the works of A.N. Glebova (1997). Redox pairs must structurally adjust to each other, then the transfer becomes possible. By selecting the components of the solution, one can "lengthen" the distance over which an electron is transferred from the reducing agent to the oxidizing agent. With a coordinated movement of particles, an electron can be transferred over long distances by the wave mechanism. As a "corridor" can be a hydrated protein chain, etc. The probability of electron transfer to a distance of up to 100A is high. The length of the "corridor" can be increased by additives (alkali metal ions, supporting electrolytes). This opens up great opportunities in the field of controlling the composition and properties of HWC and HJA. In solutions, they play the role of a kind of "black box" filled with electrons and protons. Depending on the circumstances, he can give them to other components or replenish his "reserves". The reversibility of reactions involving them makes it possible to repeatedly participate in cyclic processes. Electrons move from one metal center to another, oscillate between them. The complex molecule remains asymmetric and can take part in redox processes. HWC and HJAC are actively involved in oscillatory processes in biological media. This type of reaction is called oscillatory reactions. They are found in enzymatic catalysis, protein synthesis and other biochemical processes accompanying biological phenomena. These include periodic processes of cellular metabolism, waves of activity in the heart tissue, in brain tissue, and processes occurring at the level of ecological systems. An important stage of metabolism is the splitting of hydrogen from nutrients. In this case, hydrogen atoms pass into the ionic state, and the electrons separated from them enter the respiratory chain and give up their energy to the formation of ATP. As we have established, titanium complexonates are active carriers of not only electrons, but also protons. The ability of titanium ions to fulfill their role in the active center of enzymes such as catalases, peroxidases and cytochromes is determined by its high ability to complex formation, the formation of coordinated ion geometry, the formation of polynuclear HVA and HJA of various compositions and properties as a function of pH, the concentration of the transition element Ti and the organic component of the complex, their molar ratio. This ability is manifested in an increase in the selectivity of the complex

in relation to substrates, products of metabolic processes, activation of bonds in the complex (enzyme) and substrate through coordination and change in the shape of the substrate in accordance with the steric requirements of the active center.

Electrochemical transformations in the body associated with the transfer of electrons are accompanied by a change in the degree of oxidation of particles and the appearance of a redox potential in solution. A large role in these transformations belongs to the multinuclear HVA and HNA complexes. They are active regulators of free radical processes, a system for the utilization of reactive oxygen species, hydrogen peroxide, oxidizing agents, radicals, and are involved in the oxidation of substrates, as well as in maintaining antioxidant homeostasis, in protecting the body from oxidative stress. Their enzymatic action on biosystems is similar to enzymes (cytochromes, superoxide dismutase, catalase, peroxidase, glutathione reductase, dehydrogenases). All this indicates high antioxidant properties of complexonates of transition elements.

7.14. QUESTIONS AND TASKS FOR SELF-CHECKING OF PREPAREDNESS FOR LESSONS AND EXAMS

1. Give the concept of complex compounds. How do they differ from double salts, and what do they have in common?

2. Make formulas of complex compounds according to their name: ammonium dihydroxotetrachloroplatinate (IV), triammintrinitrocobalt (III), give their characteristics; indicate the internal and external coordination sphere; the central ion and the degree of its oxidation: ligands, their number and denticity; the nature of the connections. Write the dissociation equation in an aqueous solution and the expression for the stability constant.

3. General properties of complex compounds, dissociation, stability of complexes, chemical properties of complexes.

4. How is the reactivity of complexes characterized from thermodynamic and kinetic positions?

5. Which amino complexes will be more durable than tetraamino-copper (II), and which ones will be less durable?

6. Give examples of macrocyclic complexes formed by alkali metal ions; d-element ions.

7. On what basis are complexes classified as chelated? Give examples of chelate and non-chelate complex compounds.

8. Using the example of copper glycinate, give the concept of intracomplex compounds. Write the structural formula of magnesium complexonate with ethylenediaminetetraacetic acid in sodium form.

9. Give a schematic structural fragment of any polynuclear complex.

10. Define polynuclear, heteronuclear and heterovalent complexes. The role of transition metals in their formation. The biological role of these components.

11. What types of chemical bonds are found in complex compounds?

12. List the main types of hybridization of atomic orbitals that can occur at the central atom in the complex. What is the geometry of the complex depending on the type of hybridization?

13. Based on the electronic structure of the atoms of the elements of s-, p- and d-blocks, compare the ability to complex formation and their place in the chemistry of complexes.

14. Define complexones and complexonates. Give examples of the most used in biology and medicine. Give the thermodynamic principles on which chelation therapy is based. The use of complexonates for the neutralization and elimination of xenobiotics from the body.

15. Consider the main cases of violation of metal-ligand homeostasis in the human body.

16. Give examples of biocomplex compounds containing iron, cobalt, zinc.

17. Examples of competing processes involving hemoglobin.

18. The role of metal ions in enzymes.

19. Explain why for cobalt in complexes with complex ligands (polydentate) the oxidation state +3 is more stable, and in ordinary salts, such as halides, sulfates, nitrates, the oxidation state is +2?

20. For copper, oxidation states +1 and +2 are characteristic. Can copper catalyze electron transfer reactions?

21. Can zinc catalyze redox reactions?

22. What is the mechanism of action of mercury as a poison?

23. Indicate the acid and base in the reaction:

AgNO 3 + 2NH 3 \u003d NO 3.

24. Explain why the potassium-sodium salt of hydroxyethylidene diphosphonic acid, and not HEDP, is used as a drug.

25. How is the transport of electrons in the body carried out with the help of metal ions, which are part of biocomplex compounds?

7.15. TESTS

1. The oxidation state of the central atom in the complex ion is 2- is equal to:

a)-4;

b) +2;

at 2;

d) +4.

2. The most stable complex ion:

a) 2-, Kn = 8.5x10 -15;

b) 2-, Kn = 1.5x10 -30;

c) 2-, Kn = 4x10 -42;

d) 2-, Kn = 1x10 -21.

3. The solution contains 0.1 mol of the PtCl 4 4NH 3 compound. Reacting with AgNO 3 , it forms 0.2 mol of AgCl precipitate. Give the starting substance the coordination formula:

a)Cl;

b) Cl 3 ;

c) Cl 2 ;

d) Cl 4 .

4. What is the shape of the complexes formed as a result of sp 3 d 2-gi- breeding?

1) tetrahedron;

2) square;

4) trigonal bipyramid;

5) linear.

5. Choose the formula for the compound pentaamminechlorocobalt (III) sulfate:

a) Na 3 ;

6) [CoCl 2 (NH 3) 4 ]Cl;

c) K 2 [Co(SCN) 4];

d) SO 4 ;

e) [Co(H 2 O) 6 ] C1 3 .

6. What ligands are polydentate?

a) C1 -;

b) H 2 O;

c) ethylenediamine;

d) NH 3 ;

e) SCN - .

7. Complexing agents are:

a) electron pair donor atoms;

c) atoms- and ions-acceptors of electron pairs;

d) atoms- and ions-donors of electron pairs.

8. The elements with the least complexing ability are:

a)s; c) d;

b) p; d) f

9. Ligands are:

a) electron pair donor molecules;

b) ions-acceptors of electron pairs;

c) molecules- and ions-donors of electron pairs;

d) molecules- and ions-acceptors of electron pairs.

10. Communication in the internal coordination sphere of the complex:

a) covalent exchange;

b) covalent donor-acceptor;

c) ionic;

d) hydrogen.

11. The best complexing agent will be:

As you know, metals tend to lose electrons and, thereby, form. Positively charged metal ions can be surrounded by anions or neutral molecules, forming particles called comprehensive and capable of independent existence in a crystal or solution. And compounds containing complex particles in the nodes of their crystals are called complex compounds.

Structure of complex compounds

1. Most complex compounds have inner and outer spheres . When writing the chemical formulas of complex compounds, the inner sphere is enclosed in square brackets. For example, in complex compounds K and Cl 2, the inner sphere is the groups of atoms (complexes) - - and 2+, and the outer sphere is the K + and Cl ions - respectively.
2. Central atom or ion the inner sphere is called complexing agent. Usually, metal ions with a sufficient amount of free ones act as complexing agents - these are p-, d-, f- elements: Cu 2+, Pt 2+, Pt 4+, Ag +, Zn 2+, Al 3+, etc. But it can also be atoms of elements that form non-metals. The charge of the complexing agent is usually positive, but it can also be negative or zero and equal to the sum of the charges of all other ions. In the examples above, the complexing agents are Al 3+ and Ca 2+ ions.

1. The complexing agent is surrounded and is associated with ions of the opposite sign or neutral molecules, the so-called ligands. Anions such as F - , OH - , CN - , CNS - , NO 2 - , CO 3 2- , C 2 O 4 2- , etc., or neutral molecules of H 2 O, NH 3 , CO, NO, etc. In our examples, these are OH ions - and NH 3 molecules. The number of ligands in various complex compounds ranges from 2 to 12. And the number of ligands itself (the number of sigma bonds) is called coordination number (c.h.) of the complexing agent. In the considered examples, c.ch. equals 4 and 8.

1. Complex charge(inner sphere) is defined as the sum of the charges of the complexing agent and ligands.
2. outer sphere form ions associated with the complex by ionic or intermolecular bonds and having a charge whose sign is opposite to that of the charge of the complexing agent. The numerical value of the charge of the outer sphere coincides with the numerical value of the charge of the inner sphere. In the formula of a complex compound, they are written in square brackets. The outer sphere may even be absent if the inner sphere is neutral. In the given examples, the outer sphere is formed by 1 K + ion and 2 Cl - ions, respectively.

Classification of complex compounds

Based on different principles, complex compounds can be classified in different ways:

1. By electric charge: cationic, anionic and neutral complexes.

• Cation complexes have a positive charge and are formed if neutral molecules are coordinated around a positive ion. For example, Cl 3 , Cl 2
• Anion complex s have a negative charge and are formed if atoms with negative are coordinated around a positive ion. For example, K, K 2
• Neutral complexes have zero charge and no outer sphere. They can be formed upon coordination around an atom of molecules, as well as upon simultaneous coordination around a central positively charged ion of negative ions and molecules.

1. By the number of complexing agents

• single core - the complex contains one central atom, for example, K 2
• multi-core e- the complex contains two or more central atoms, for example,

1. By type of ligand

• Hydrates – contain aqua-complexes, i.e. water molecules act as ligands. For example, Br 3 , Br 2
• Ammonia - contain ammine complexes, in which ammonia molecules (NH 3) act as ligands. For example, Cl 2 , Cl
• carbonyls – in such complex compounds, carbon monoxide molecules act as ligands. For example, , .
• acidocomplexes - complex compounds containing acidic residues of both oxygen-containing and anoxic acids as ligands (F -, Cl -, Br -, I -, CN -, NO 2 -, SO 4 2–, PO 4 3–, etc., as well as OH-). For example, K 4 , Na 2
• Hydroxocomplexes - complex compounds in which hydroxide ions act as ligands: K 2, Cs 2

Complex compounds may contain ligands belonging to various classes of the above classification. For example: K, Br

1. By chemical properties: acids, bases, salts, non-electrolytes:

• acids — H, H2
• Foundations - (OH) 2,OH
• salt — Cs 3 , Cl 2
• Non-electrolytes —

1. According to the number of places occupied by the ligand in the coordination sphere

In the coordination sphere, ligands can occupy one or more places, i.e. form one or more bonds with the central atom. On this basis, they distinguish:

• Monodentate ligands - these are ligands such as molecules of H 2 O, NH 3, CO, NO, etc. and nones CN - , F - , Cl - , OH - , SCN - , etc.
• Bidentate ligands . This type of ligand includes ions H 2 N-CH 2 -COO -, CO 3 2-, SO 4 2-, S 2 O 3 2-, an ethylenediamine molecule H 2 N-CH 2 -CH 2 -H 2 N (abbreviated en).
• Polydentate ligands . These are, for example, organic ligands containing several groups - CN or -COOH (EDTA). Some polydentate ligands are capable of forming cyclic complexes called chelate (for example, hemoglobin, chlorophyll, etc.)

Nomenclature of complex compounds

To burn the formula of the complex compound, it must be remembered that, like any ionic compound, the cation formula is written first, and then the anion formula. In this case, the formula of the complex is written in square brackets, where the complexing agent is written first, then the ligands.

And here are a few rules, following which it will not be difficult to compose the name of a complex compound:

1. In the names of complex compounds, as well as ionic salts, the anion is listed first, followed by the cation.
2. In the name of the complex ligands are listed first, and then the complexing agent. The ligands are listed in alphabetical order.
3. Neutral ligands have the same name as molecules, the ending is added to anionic ligands -O. The table below lists the names of the most common ligands.

ligand	Ligand name	ligand	Ligand name
en	ethylenediamine	O 2-	Okso
H2O	Aqua	H-	Hydrido
NH3	Ammin	H+	Hydro
CO	carbonyl	oh-	hydroxo
NO	Nitrosyl	SO 4 2-	Sulfato
NO-	Nitroso	CO 3 2-	carbonato
NO 2 -	Nitro	CN-	Cyano
N 3 -	Azido	NCS-	Thiocionato
Cl-	Chloro	C 2 O 4 2-	Oxalato
br-	Bromo

1. If the number of ligands is greater than one, then their number is indicated by Greek prefixes:

2-di-, 3-tri-, 4-tetra-, 5-penta-, 6-hexa-, 7-hepta-, 8-octa-, 9-nona-, 10-deca-.

If the name of the ligand itself already contains a Greek prefix, then the name of the ligand is written in brackets and a prefix of the type is added to it:

2-bis-, 3-tris-, 4-tetrakis-, 5-pentakis-, 6-hexakis-.

For example, the Cl 3 compound is called tris(ethylenediamine)cobalt(III).

1. The names of complex anions end suffix - at
2. After the name of the metal in parentheses indicate Roman numerals for its oxidation state.

For example, let's call the following connections:

• Cl

Let's start with ligands: 4 water molecules are designated as tetraaqua, and 2 chloride ions are designated as dichloro.

Finally, anion in this connection is chloride ion.

tetraaquadichlorochromium chloride(III)

• K4

Let's start with ligands: the complex anion contains 4 ligands CN - , which are called tetracyano.

Since the metal is part of the complex anion, it is called nickelate(0).

So the full title is: potassium tetracyanonickelate(0)

Categories ,

Complex compounds These are molecular or ionic compounds formed by attaching a metal or non-metal, neutral molecules or other ions to an atom or ion. They are able to exist both in a crystal and in solution.

Basic provisions and concepts of coordination theory.

To explain the structure and properties of complex compounds in 1893, the Swiss chemist A. Werner proposed a coordination theory into which he introduced two concepts: coordination and side valency.

According to Werner main valence valence is called by means of which atoms are connected to form simple compounds that obey the theory

valency. But, having exhausted the main valence, the atom is capable, as a rule, of further attachment due to side valence, as a result of the manifestation of which a complex compound is formed.

Under the influence of the forces of the main and secondary valency, atoms tend to evenly surround themselves with ions or molecules and are thus the center of attraction. Such atoms are called central or complexing agents. Ions or molecules that are directly bound to the complexing agent are called ligands.

By means of the main valency, ligands are attached to ions, and by means of secondary valency, ions and molecules are attached.

The attraction of a ligand to a complexing agent is called coordination, and the number of ligands is called the coordination number of the complexing agent.

We can say that complex compounds are compounds whose molecules consist of a central atom (or ion) directly associated with a certain number of other molecules or ions, called ligands.

Metal cations most often act as complexing agents (Co +3, Pt +4, Cr +3, Cu +2 Au +3, etc.)

The ligands can be ions Cl -, CN -, NCS -, NO 2 -, OH -, SO 4 2- and neutral molecules NH 3, H 2 O, amines, amino acids, alcohols, thioalcohols, PH 3, ethers.

The number of coordination sites occupied by the ligand near the complexing agent is called its coordination capacity or denticity.

Ligands attached to the complexing agent by one bond occupy one coordination site and are called monodentate (Cl - , CN - , NCS -). If the ligand is attached to the complexing agent through several bonds, then it is polydentate. For example: SO 4 2- , CO 3 2- are bidentate.

The complexing agent and ligands make up inner sphere compounds or complex (in the formulas, the complex is enclosed in square brackets). Ions that are not directly bound to the complexing agent are outer coordination sphere.

The ions of the outer sphere are less strongly bound than the ligands and are spatially removed from the complexing agent. They are easily replaced by other ions in aqueous solutions.

For example, in the K 3 compound, the complexing agent is Fe +2, the ligands are CN -. Two ligands are attached due to the main valence, and 4 - due to the secondary valency, therefore the coordination number is 6.

Ion Fe +2 with ligands CN - make up inner sphere or complex, and K ions + outer coordination sphere:

As a rule, the coordination number is equal to twice the charge of the metal cation, for example: singly charged cations have a coordination number equal to 2, 2-charged - 4, and 3-charged - 6. If the element exhibits a variable oxidation state, then with an increase in its coordination number increases. For some complexing agents, the coordination number is constant, for example: Co +3, Pt +4, Cr +3 have a coordination number of 6, for ions B +3, Be +2, Cu +2, Au +3 the coordination number is 4. for For most ions, the coordination number is variable and depends on the nature of the ions in the outer sphere and on the conditions for the formation of complexes.