Compounds of manganese (II), (III), (IV), properties of oxides and hydroxides, manganese salts, their properties; manganese dioxide, its properties. Manganese Other binary compounds

Manganese is a hard, gray metal. Its atoms have an outer shell electron configuration

Manganese metal reacts with water and reacts with acids to form manganese(II) ions:

In various compounds, manganese exhibits oxidation states. The higher the oxidation state of manganese, the greater the covalent nature of its corresponding compounds. As the degree of oxidation of manganese increases, the acidity of its oxides also increases.

Manganese(II)

This form of manganese is the most stable. It has an external electronic configuration with one electron in each of the five orbitals.

In aqueous solution, manganese(II) ions hydrate to form a pale pink complex ion, hexaaquamanganese(II). This ion is stable in acidic environments, but forms a white precipitate of manganese hydroxide in alkaline environments. Manganese(II) oxide has the properties of basic oxides.

Manganese(III)

Manganese (III) exists only in complex compounds. This form of manganese is unstable. In an acidic environment, manganese(III) disproportionates into manganese(II) and manganese(IV).

Manganese (IV)

The most important compound of manganese(IV) is the oxide. This black compound is insoluble in water. It is assigned an ionic structure. Stability is due to the high enthalpy of the lattice.

Manganese(IV) oxide has weakly amphoteric properties. It is a strong oxidizing agent, for example it displaces chlorine from concentrated hydrochloric acid:

This reaction can be used to produce chlorine in the laboratory (see Section 16.1).

Manganese(VI)

This oxidation state of manganese is unstable. Potassium manganate (VI) can be obtained by fusing manganese (IV) oxide with some strong oxidizing agent, for example potassium chlorate or potassium nitrate:

Potassium manganate (VI) is green in color. It is stable only in alkaline solution. In an acidic solution it disproportionates into manganese (IV) and manganese (VII):

Manganese (VII)

Manganese has this oxidation state in a strongly acidic oxide. However, the most important manganese(VII) compound is potassium manganate(VII) (potassium permanganate). This solid dissolves very well in water, forming a dark purple solution. Manganate has a tetrahedral structure. In a slightly acidic environment, it gradually decomposes, forming manganese (IV) oxide:

In an alkaline environment, potassium manganate(VII) is reduced, forming first green potassium manganate(VI) and then manganese(IV) oxide.

Potassium manganate (VII) is a strong oxidizing agent. In a sufficiently acidic environment, it is reduced, forming manganese(II) ions. The standard redox potential of this system is , which exceeds the standard potential of the system and therefore the manganate oxidizes the chloride ion to chlorine gas:

The oxidation of manganate chloride ion proceeds according to the equation

Potassium manganate(VII) is widely used as an oxidizing agent in laboratory practice, e.g.

to produce oxygen and chlorine (see Chapters 15 and 16);

to carry out an analytical test for sulfur dioxide and hydrogen sulfide (see Chapter 15); in preparative organic chemistry (see Chapter 19);

as a volumetric reagent in redox titrimetry.

An example of the titrimetric use of potassium manganate (VII) is the quantitative determination with its help of iron (II) and ethanedioates (oxalates):

However, since potassium manganate (VII) is difficult to obtain in high purity, it cannot be used as a primary titrimetric standard.

general review

Manganese is element VIIB of the IV period subgroup. The electronic structure of the atom is 1s 2 2s 2 2p 6 3s 2 3p 6 3d 5 4s 2, the most characteristic oxidation states in compounds are from +2 to +7.

Manganese is a fairly common element, making up 0.1% (mass fraction) of the earth's crust. Found in nature only in the form of compounds, the main minerals are pyrolusite (manganese dioxide MnO2.), gauskanite Mn3O4 and brownite Mn2O3.

Physical properties

Manganese is a silvery-white, hard, brittle metal. Its density is 7.44 g/cm 3, melting point is 1245 o C. Four crystalline modifications of manganese are known.

Chemical properties

Manganese is an active metal; in a number of voltages it is between aluminum and zinc. In air, manganese is covered with a thin oxide film, which protects it from further oxidation even when heated. In a finely crushed state, manganese oxidizes easily.

3Mn + 2O 2 = Mn 3 O 4– when calcined in air

Water at room temperature acts on manganese very slowly, but when heated it acts faster:

Mn + H 2 O = Mn(OH) 2 + H 2

It dissolves in dilute hydrochloric and nitric acids, as well as in hot sulfuric acid (in cold H2SO4 it is practically insoluble):

Mn + 2HCl = MnCl 2 + H 2 Mn + H 2 SO 4 = MnSO 4 + H 2

Receipt

Manganese is obtained from:

1. electrolysis of solution MnSO 4. In the electrolytic method, the ore is reduced and then dissolved in a mixture of sulfuric acid and ammonium sulfate. The resulting solution is subjected to electrolysis.

2. reduction from its oxides with silicon in electric furnaces.

Application

Manganese is used:

1. in the production of alloy steels. Manganese steel, containing up to 15% manganese, has high hardness and strength.

2. manganese is part of a number of magnesium-based alloys; it increases their resistance to corrosion.

Magrane oxides

Manganese forms four simple oxides - MnO, Mn2O3, MnO2 And Mn2O7 and mixed oxide Mn3O4. The first two oxides have basic properties, manganese dioxide MnO2 is amphoteric, and the higher oxide Mn2O7 is permanganic acid anhydride HMnO4. Manganese(IV) derivatives are also known, but the corresponding oxide MnO3 not received.

Manganese(II) compounds

Oxidation state +2 corresponds to manganese (II) oxide MnO, manganese hydroxide Mn(OH) 2 and manganese(II) salts.

Manganese(II) oxide is obtained in the form of a green powder by reducing other manganese oxides with hydrogen:

MnO 2 + H 2 = MnO + H 2 O

or during thermal decomposition of manganese oxalate or carbonate without air access:

MnC 2 O 4 = MnO + CO + CO 2 MnCO 3 = MnO + CO 2

When alkalis act on solutions of manganese (II) salts, a white precipitate of manganese hydroxide Mn(OH)2 precipitates:

MnCl 2 + NaOH = Mn(OH) 2 + 2NaCl

In air it quickly darkens, oxidizing into brown manganese(IV) hydroxide Mn(OH)4:

2Mn(OH) 2 + O 2 + 2H 2 O =2 Mn(OH) 4

Manganese (II) oxide and hydroxide exhibit basic properties and are easily soluble in acids:

Mn(OH)2 + 2HCl = MnCl 2 + 2H 2 O

Manganese (II) salts are formed when manganese is dissolved in dilute acids:

Mn + H 2 SO 4 = MnSO 4 + H 2- when heated

or by the action of acids on various natural manganese compounds, for example:

MnO 2 + 4HCl = MnCl 2 + Cl 2 + 2H 2 O

In solid form, manganese (II) salts are pink in color; solutions of these salts are almost colorless.

When interacting with oxidizing agents, all manganese (II) compounds exhibit reducing properties.

Manganese(IV) compounds

The most stable manganese(IV) compound is dark brown manganese dioxide. MnO2. It is easily formed both during the oxidation of lower and during the reduction of higher manganese compounds.

MnO2- an amphoteric oxide, but both acidic and basic properties are very weakly expressed.

In an acidic environment, manganese dioxide is a strong oxidizing agent. When heated with concentrated acids, the following reactions occur:

2MnO 2 + 2H 2 SO 4 = 2MnSO 4 + O 2 + 2H 2 O MnO 2 + 4HCl = MnCl 2 + Cl 2 + 2H 2 O

Moreover, in the first stage in the second reaction, unstable manganese (IV) chloride is first formed, which then decomposes:

MnCl 4 = MnCl 2 + Cl 2

When fusion MnO2 Manganites are obtained with alkalis or basic oxides, for example:

MnO 2 +2KOH = K 2 MnO 3 + H 2 O

When interacting MnO2 with concentrated sulfuric acid manganese sulfate is formed MnSO4 and oxygen is released:

2Mn(OH) 4 + 2H2SO 4 = 2MnSO 4 + O 2 + 6H 2 O

Interaction MnO2 with stronger oxidizing agents leads to the formation of manganese (VI) and (VII) compounds, for example, when fused with potassium chlorate, potassium manganate is formed:

3MnO 2 + KClO 3 + 6KOH = 3K2MnO 4 + KCl + 3H 2 O

and when exposed to polonium dioxide in the presence of nitric acid - manganese acid:

2MnO 2 + 3PoO 2 + 6HNO 3 = 2HMnO 4 + 3Po(NO 3) 2 + 2H 2 O

Applications of MnO 2

As an oxidizing agent MnO2 used in the production of chlorine from hydrochloric acid and in dry galvanic cells.

Manganese(VI) and (VII) compounds

When manganese dioxide is fused with potassium carbonate and nitrate, a green alloy is obtained, from which dark green crystals of potassium manganate can be isolated K2MnO4- salts of very unstable permanganic acid H2MnO4:

MnO 2 + KNO 3 + K 2 CO 3 = K 2 MnO 4 + KNO 2 + CO 2

in an aqueous solution, manganates spontaneously transform into salts of manganese acid HMnO4 (permanganates) with the simultaneous formation of manganese dioxide:

3K 2 MnO 4 + H 2 O = 2KMnO 4 + MnO 2 + 4KOH

in this case, the color of the solution changes from green to crimson and a dark brown precipitate is formed. In the presence of alkali, manganates are stable; in an acidic environment, the transition of manganate to permanganate occurs very quickly.

When strong oxidizing agents (for example, chlorine) act on a manganate solution, the latter is completely converted into permanganate:

2K 2 MnO 4 + Cl 2 = 2KMnO 4 + 2KCl

Potassium permanganate KMnO4- the most famous salt of permanganic acid. It appears as dark purple crystals, moderately soluble in water. Like all manganese (VII) compounds, potassium permanganate is a strong oxidizing agent. It easily oxidizes many organic substances, converts iron(II) salts into iron(III) salts, oxidizes sulfurous acid into sulfuric acid, releases chlorine from hydrochloric acid, etc.

In redox reactions KMnO4(and he MnO4-)can be restored to varying degrees. Depending on the pH of the medium, the reduction product may be an ion Mn 2+(in an acidic environment), MnO2(in a neutral or slightly alkaline environment) or ion MnO4 2-(in a highly alkaline environment), for example:

KMnO4 + KNO 2 + KOH = K 2 MnO 4 + KNO 3 + H 2 O- in a highly alkaline environment 2KMnO 4 + 3KNO 2 + H 2 O = 2MnO 2 + 3KNO 3 + 2KOH– in neutral or slightly alkaline 2KMnO 4 + 5KNO 2 + 3H 2 SO 4 = 2MnSO 4 + K 2 SO 4 + 5KNO 3 + 3H 2 O– in an acidic environment

When heated in dry form, potassium permanganate already at a temperature of about 200 o C decomposes according to the equation:

2KMnO 4 = K 2 MnO 4 + MnO 2 + O 2

Free permanganate acid corresponding to permanganates HMnO4 has not been obtained in the anhydrous state and is known only in solution. The concentration of its solution can be increased to 20%. HMnO4- a very strong acid, completely dissociated into ions in an aqueous solution.

Manganese (VII) oxide, or manganese anhydride, Mn2O7 can be prepared by the action of concentrated sulfuric acid on potassium permanganate: 2KMnO 4 + H 2 SO 4 = Mn 2 O 7 + K 2 SO 4 + H 2 O

Manganese anhydride is a greenish-brown oily liquid. It is very unstable: when heated or in contact with flammable substances, it explodes into manganese dioxide and oxygen.

As an energetic oxidizing agent, potassium permanganate is widely used in chemical laboratories and industries; it also serves as a disinfectant. The thermal decomposition reaction of potassium permanganate is used in the laboratory to produce oxygen.

] interpreted it as a 0-0 transition band associated with the ground state of the molecule. He attributed weaker bands at 620 nm (0-1) and 520 nm (1-0) to the same electronic transition. Nevin [42NEV, 45NEV] performed an analysis of the rotational and fine structure of the bands at 568 and 620 nm (5677 and 6237 Å) and determined the type of electronic transition 7 Π - 7 Σ. In subsequent works [48NEV/DOY, 52NEV/CON, 57HAY/MCC] the rotational and fine structure of several more bands of the 7 Π - 7 Σ (A 7 Π - X 7 Σ +) transition of MnH and MnD was analyzed.

High-resolution laser spectroscopy methods made it possible to analyze the hyperfine structure of lines in the 0-0 band A 7 Π - X 7 Σ +, due to the presence of nuclear spin in the manganese isotope 55 Mn (I = 2.5) and the 1 H proton (I = 1/2) [ 90VAR/FIE, 91VAR/FIE, 92VAR/GRA, 2007GEN/STE ].

The rotational and fine structure of several MnH and MnD bands in the near-IR and violet spectral regions was analyzed in [88BAL, 90BAL/LAU, 92BAL/LIN]. It was established that the bands belong to four quintet transitions with a common lower electronic state: b 5 Π i - a 5 Σ + , c 5 Σ + - a 5 Σ + , d 5 Π i - a 5 Σ + and e 5 Σ + - a 5 Σ + .

The vibrational-rotational spectrum of MnH and MnD was obtained in the works. An analysis of the rotational and fine structure of vibrational transitions (1-0), (2-1), (3-2) in the ground electronic state of X 7 Σ + was performed.

The spectra of MnH and MnD in a low-temperature matrix were studied in [78VAN/DEV, 86VAN/GAR, 86VAN/GAR2, 2003WAN/AND]. The vibrational frequencies of MnH and MnD in solid argon [78VAN/DEV, 2003WAN/AND], neon and hydrogen [2003WAN/AND] are close to the value ΔG 1/2 in the gas phase. The magnitude of the matrix shift (maximum in argon for MnH ~ 11 cm -1) is typical for molecules with a relatively ionic bond.

The electron paramagnetic resonance spectrum obtained in [78VAN/DEV] confirmed the symmetry of the ground state 7 Σ. The hyperfine structure parameters obtained in [78VAN/DEV] were refined in [86VAN/GAR, 86VAN/GAR2] when analyzing the electron-nuclear double resonance spectrum.

The photoelectron spectrum of the MnH- and MnD- anions was obtained in [83STE/FEI]. The spectrum identifies transitions both to the ground state of the neutral molecule and those excited with energy T 0 = 1725±50 cm -1 and 11320±220 cm -1 . For the first excited state, a vibrational progression from v = 0 to v = 3 was observed, and the vibrational constants w e = 1720±55 cm -1 and w e were determined x e = 70±25 cm -1. The symmetry of the excited states has not been determined; only assumptions have been made based on theoretical concepts [83STE/FEI, 87MIL/FEI]. Data obtained later from the electronic spectrum [88BAL, 90BAL/LAU] and the results of theoretical calculations [89LAN/BAU] unambiguously showed that the excited states in the photoelectron spectrum are a 5 Σ + and b 5 Π i.

Ab initio calculations of MnH were performed using various methods in the works [73BAG/SCH, 75BLI/KUN, 81DAS, 83WAL/BAU, 86CHO/LAN, 89LAN/BAU, 96FUJ/IWA, 2003WAN/AND, 2004RIN/TEL, 2005BAL/PET, 2006FUR/ PER, 2006KOS/MAT]. In all works, the parameters of the ground state were obtained, which, according to the authors, agree quite well with the experimental data.

The calculation of thermodynamic functions included: a) ground state X 7 Σ + ; b) experimentally observed excited states; c) states d 5 Δ and B 7 Σ +, calculated in [89LAN/BAU]; d) synthetic (estimated) states, taking into account other bound states of the molecule up to 40000 cm -1.

The vibrational constants of the ground state of MnH and MnD were obtained in [52NEV/CON, 57HAY/MCC] and with very high accuracy in [89URB/JON, 91URB/JON, 2005GOR/APP]. In table Mn.4 values ​​are from [2005GOR/APP].

The rotational constants of the ground state of MnH and MnD were obtained in [42NEV, 45NEV, 48NEV/DOY, 52NEV/CON, 57HAY/MCC, 74PAC, 75KOV/PAC, 89URB/JON, 91URB/JON, 92VAR/GRA, 2005GOR/APP, 2007GEN /STE]. The differences in the values ​​of B0 are within 0.001 cm -1, B e - within 0.002 cm -1. They are due to different measurement accuracy and different data processing methods. In table Mn.4 values ​​are from [2005GOR/APP].

The energies of the observed excited states were obtained as follows. For the state a 5 Σ + the value T 0 is taken from [ 83STE/FEI ] (see above in the text). For other quintet states in Table. Mn.4 the energies obtained by adding to T 0 a 5 Σ + the values ​​T = 9429.973 cm -1 and T = 11839.62 cm -1 [ 90BAL/LAU ], T 0 = 20880.56 cm -1 and T 0 = 22331.25 cm -1 are given [92BAL/LIN]. For state A 7 Π shows the value of T e from [84HU/GER].

State energy d 5 D, calculated in [89LAN/BAU], is reduced by 2000 cm -1, which corresponds to the difference between the experimental and calculated energy of state b 5 Π i . The energy of B 7 Σ + is estimated by adding to the experimental energy A 7 Π energy differences of these states on the graph of potential curves [89LAN/BAU].

The vibrational and rotational constants of the excited states of MnH were not used in the calculations of thermodynamic functions and are given in Table Mn.4 for reference. The vibrational constants are given according to data from [ 83STE/FEI ] (a 5 Σ +), [ 90BAL/LAU ] ( c 5 Σ +), [ 92BAL/LIN ] ( d 5 Πi, e 5 Σ +), [ 84HUY/GER ] ( A 7 Π). Rotation constants are given according to data from [90BAL/LAU] ( b 5 Πi, c 5 Σ +), [ 92BAL/LIN ] (a 5 Σ + , d 5 Πi, e 5 Σ +), [ 92VAR/GRA ] ( B 0 and D 0 A 7 Π) and [ 84HUGH/GER ] (a 1 A 7 Π).

To estimate the energies of unobserved electronic states, the Mn + H - ionic model was used. According to the model, below 20000 cm -1 the molecule has no states other than those that have already been taken into account, i.e. those states that were observed in the experiment and/or calculated [89LAN/BAU]. Above 20000 cm -1 the model predicts a large number of additional electronic states belonging to three ionic configurations: Mn + (3d 5 4s)H - , Mn + (3d 5 4p)H - and Mn + (3d 6)H - . These states compare well with the states calculated in [2006KOS/MAT]. The energies of states estimated from the model are partly more accurate because they take into account experimental data. Due to the large number of states assessed above 20000 cm -1, they are combined into synthetic states at several energy levels (see note Table Mn.4).

Thermodynamic functions MnH(g) were calculated using equations (1.3) - (1.6) , (1.9) , (1.10) , (1.93) - (1.95) . Values Q int and its derivatives were calculated using equations (1.90) - (1.92) taking into account fourteen excited states under the assumption that Q kol.vr ( i) = (p i /p X)Q kol.vr ( X) . The vibrational-rotational partition function of the state X 7 Σ + and its derivatives were calculated using equations (1.70) - (1.75) by direct summation over energy levels. The calculations took into account all energy levels with values J< J max ,v , where J max ,v was found from conditions (1.81). The vibrational-rotational levels of the X 7 Σ + state were calculated using equations (1.65), the values ​​of the coefficients Y kl in these equations were calculated using relations (1.66) for the isotopic modification corresponding to the natural mixture of hydrogen isotopes from the molecular constants 55 Mn 1 H given in Table. Mn.4. Coefficient values Y kl , as well as the quantities v max and J lim are given in table. Mn.5.

The main errors in the calculated thermodynamic functions MnH(g) are due to the calculation method. Errors in the values ​​of Φº( T) at T= 298.15, 1000, 3000 and 6000 K are estimated to be 0.16, 0.4, 1.1 and 2.3 J×K‑1×mol‑1, respectively.

Thermodynamic functions MnH(g) were previously calculated without taking into account excited states up to 5000 K in [74SCH] and taking into account excited states up to 6000 K in [

D° 0 (MnH) = 140 ± 15 kJ× mol‑1 = 11700 ± 1250 cm‑1.

The first systematic studies of the solubility of hydrogen in manganese belong to Luckemeyer-Hasse and Schenk. They showed that the change in solubility is accompanied by an α⇔β transformation. Since they were experimenting with industrial-grade manganese, it is perhaps not surprising that their results do not agree with the quantitative values ​​found in later work carried out on high-purity manganese.
Detailed studies in the temperature range from 20 to 1300° were carried out by Sieverts and Moritz on manganese distillate, as well as by Potter and Lukens on electrolytic distilled manganese. In both cases, the pressure of hydrogen in equilibrium with the previously completely degassed metal was measured at different temperatures.
Both studies obtained very similar results. In Fig. Figure 79 shows data from Sieverts and Moritz regarding the volume of hydrogen adsorbed by 100 g of manganese in the temperature range from 20 to 1300° during heating and cooling of two samples of pure manganese.

The solubility of hydrogen in the α-modification of manganese first decreases and then increases with increasing temperature. The solubility of hydrogen in β-manganese is noticeably higher than in α-manganese; therefore, the transformation β→α is accompanied by a noticeable increase in hydrogen adsorption. Solubility in β-manganese increases with temperature.
The β→γ transformation is also accompanied by an increase in hydrogen solubility, which in γ-manganese, as well as in β-manganese, increases with temperature. The transformation is accompanied by a decrease in solubility. The solubility of hydrogen in δ-manganese increases to the melting point, and the solubility of hydrogen in liquid manganese is noticeably higher than its solubility in any of the modifications of manganese in the solid state.
Thus, changes in the solubility of hydrogen in various allotropic modifications of manganese make it possible to develop a simple and elegant method for studying the temperatures of allotropic transformations, as well as their hysteresis at different rates of heating and cooling.
The results of Potter and Lukens, in general, are very close to the results of Sieverts and Moritz, as can be seen by examining the data in Table. 47. The consistency of the results is very good, except for the change in solubility in the α phase in the temperature range from room temperature to 500°: Sieverts and Moritz found that the solubility is much higher than it follows from the data of Potter and Lukens. The reason for this discrepancy is unclear.

Potter and Lukens found that at constant temperature, the solubility of hydrogen (V) changes with pressure (P) according to the dependence:

where K is a constant.
No researcher has found any manganese hydrides.
Hydrogen content in electrolytic manganese. Since hydrogen is deposited on the cathode during electrical deposition, it is not surprising that the metal thus obtained should contain hydrogen.
The hydrogen content of electrolytic manganese and issues related to its removal were studied by Potter, Hayes and Lukens. We studied ordinary electrolytic manganese of industrial purity, which was previously kept for three months at room temperature.
Measurements of the released (emitted) volume of hydrogen were carried out at temperatures up to 1300°; the results are shown in Fig. 80.
When heated to 200°, very little gas is released, but already at 300° a very significant volume is released. A little more is released at 400°, but with subsequent heating the amount of hydrogen released changes slightly, except in cases where the solubility changes due to allotropic transformations of manganese.
It has been found that manganese contains approximately 250 cm3 of hydrogen per 100 g of metal. When heated to 400° for 1 hour in air at normal pressure, 97% of the amount that can be removed is removed. As would be expected, as the external pressure decreases, a shorter heating duration is required to remove the same amount of hydrogen.
It is believed that the hydrogen present in manganese forms a supersaturated interstitial solid solution. The effect of hydrogen on the lattice parameters of α-manganese was studied by Potter and Huber; a certain expansion (increase) of the lattice is observed (Table 48), amounting to 0.0003% at 1 cm3 of hydrogen per 100 g of metal.
Heating to remove hydrogen causes compression (shrinking) of the lattice (Table 49).

Accurate measurements of lattice parameters on samples with a high hydrogen content are very difficult, since a blurred diffraction pattern is obtained. Potter and Huber attribute this to the non-uniform distribution of gas in the metal. This blurriness does not increase with increasing hydrogen content and even decreases somewhat at higher hydrogen contents. It has been established that electrolytic manganese cannot be obtained with a hydrogen content of more than 615 cm3 per 100 g, which corresponds to two hydrogen atoms per unit cell of α-manganese. With a uniform distribution of hydrogen in the metal, one can expect an equal degree of distortion of the elementary lattices and the diffraction pattern should contain clear lines.