Manganese II

Manganese can exist in multiple oxidation states from manganese(II) to man-ganese(VII). Of these states, only the lowest three exist in cationic form. Man-ganese(II) hydrolyses at the highest pH of the divalent first series transition metals and, conversely, manganese(III) at the lowest pH of the corresponding trivalent metals. 

The ionic radii of manganese(II) and manganese(III) are taken from Shannon (1976) as 0.83 and 0.645 A, respectively. Both are for a six-coordinate ion with high spin. However, the Jahn-Teller effect is hkely to lead to stronger bonds in manganese(III), as also occurs with copper(II), with an apparent reduction in ionic radius (see Chapter 16). 

The formation of the hydrolysis species of manganese(II) and manganese(III) can be described by reaction (2.5) (M = Mn or Mn , p = 1). As indicated, only monomeric hydrolysis species have been accepted for both manganese(II) and manganese(III). Although polymeric species have been postulated for manganese(II) (Fontana and Brito, 1968), these stability constant data are not retained due to the lack of confirmatory evidence. 

Robie and Hemingway (1995) provide thermochemical data for manganosite, MnO(s), as well as the manganese(II) ion. These data can be coupled with the Gibbs energy of formation of water given in Chapter 5 to derive a solubility constant for reaction (2.13) (M = Mn , x =l). The solubility constant derived 

There have been a number of determinations of the solubility of Mn(OH)2(s) (Oka, 1938 Fox, Swinehart and Garrett, 1941 Nasanen, 1942a Kovalenko, 1956 Feitknecht and Schindler, 1963), all of which are in good agreement. The datum of Kovalenko was obtained at 22 °C, whereas all of the other values relate to 25 C. The data relate to reaction (2.13) (M = Mn , x = 0). The average of the 25 C data is retained in this review  

Dilute mineral acids and also acetic acid dissolve it with the production of manganese(II) salts and hydrogen  

When it is attacked by hot, concentrated sulphuric acid, sulphur dioxide is evolved  

The manganese(II) cations are derived from manganese(II) oxide. They form colourless salts, though if the compound contains water of crystallization, and in solutions, they are slightly pink this is due to the presence of the hexaquo-manganate(II) ion, [Mn(H20)6]2+. 

Manganese(VI) compounds contain the manganate(VI) MnO anion. This is stable in alkaline solutions, and possesses a green colour. Upon neutralization a disproportionation reaction takes place manganese dioxide precipitate and manganate(VII) (permanganate) ions are formed  

The relaxation mechanisms for such an ion are bound to the zero field splitting modulation (Table 5.6), which may arise from rotation of the complex or, more probably, from distortions of the coordination sphere as a result of collisions with solvent molecules (Eqs. (3.11) and (3.12)). 

The H NMRD profiles of Mn(OH2)g+ in water solution show two dispersions (Fig. 5.43). The first (at ca. 0.05 MHz, at 298 K) is attributed to the contact relaxation and the second (at ca. 7 MHz, at 298 K) to the dipolar relaxation. From the best fit procedure, the electron relaxation time, given by rso = 3.5 x 10 9 and r = 5.3 x 10 12 s, is consistent with the position of the first dispersion, the rotational correlation time xr = 3.2 x 10 11 s is consistent with the position of the second dispersion and is in accordance with the value expected for hexaaquametal(II) complexes, the water proton-metal center distance is 2.7 A and the constant of contact interaction is 0.65 MHz (see Table 5.6). The impressive increase of / 2 at high fields is due to the field dependence of the electron relaxation time and to the presence of a non-dispersive zs term in the equation for contact relaxation (see Section 3.7.2). If it were not for the finite residence time, xm, of the water molecules in the coordination sphere, the increase in Ri could continue as long as the electron relaxation time increases. 

Summary of the H NMRD parameters for some aqua ion complexes at 298 Ka 

Metal ion / 5 A/h (MHz) ts0 (ps) tv (ps) tc Main electron relaxation mechanism Reference 

In all Mn(II) proteins and in most complexes the contact interaction is found negligible. In fact, the H NMRD profile of MnEDTA, for instance, indicates the presence of the dipolar contribution only, and one water bound to the complex. The relaxation rate of manganese(II) complexes with DTPA (see Fig. 5.56) is instead provided by outer-sphere relaxation only, since no water molecules are bound to the complex (see Section 4.5.2). 

---

Manufactured by the liquid-phase oxidation of ethanal at 60 C by oxygen or air under pressure in the presence of manganese(ii) ethanoate, the latter preventing the formation of perelhanoic acid. Another important route is the liquid-phase oxidation of butane by air at 50 atm. and 150-250 C in the presence of a metal ethanoate. Some ethanoic acid is produced by the catalytic oxidation of ethanol. Fermentation processes are used only for the production of vinegar. 

The following redox potentials are given for the oxidation of manganese(II) to manganese(III) in acid and alkaline solution. 

Manganate(VII) is reduced to manganese(II) ion in acid solution (usually sulphuric acid) ... 

Manganese is the third most abundant transition metal, and is widely distributed in the earth s crust. The most important ore is pyrolusite, manganese(IV) oxide. Reduction of this ore by heating with aluminium gives an explosive reaction, and the oxide Mn304 must be used to obtain the metal. The latter is purified by distillation in vacuo just above its melting point (1517 K) the pure metal can also he obtained by electrolysis of aqueous manganese(II) sulphate. 

The metal looks like iron it exists in four allotropic modifications, stable over various temperature ranges. Although not easily attacked by air. it is slowly attacked by water and dissolves readily in dilute acids to give manganese(II) salts. The stable form of the metal at ordinary temperatures is hard and brittle—hence man ganese is only of value in alloys, for example in steels (ferroalloys) and with aluminium, copper and nickel. 

Manganese(IV) oxide is the only familiar example of this oxidation state. It occurs naturally as pyrolusite, but can be prepared in an anhydrous form by strong heating of manganese(II) nitrate ... 

It can also be precipitated in a hydrated form by the oxidation of a manganese(II) salt, by, for example, a peroxodisulphate ... 

However the Mn (aq) ion can be stabilised by using acid solutions or by complex formation it can be prepared by electrolytic oxidation of manganese(II) solutions. The alum CaMn(S04)2.12H2O contains... 

The complexes of manganese(III) include [Mn(CN)g] (formed when manganesefll) salts are oxidised in presence of cyanide ions), and [Mnp5(H20)] , formed when a manganese(II) salt is oxidised by a manganate(VII) in presence of hydrofluoric acid ... 

How ever, the Mn(II) ion forms a variety of complexes in solution, some of which may be more easily oxidised these complexes can be either tetrahedral, for example [MnClJ , or octahedral, for example [Mn(CN)f,] Addition of ammonia to an aqueous solution of a manganese(II) salt precipitates Mn(OH)2 reaction of ammonia with anhydrous manganese(II) salts can yield the ion [MnfNH y T... 

Halite, see Sodium chloride Hausmannite, see Manganese(II,IV) oxide Heavy hydrogen, see HydrogenpH] or name followed by -d... 

Sylvite, see Potassium chloride Szmikite, see Manganese(II) sulfate hydrate... 

Manganese(II) can be titrated directly to Mn(III) using hexacyanoferrate(III) as the oxidant. Alternatively, Mn(III), prepared by oxidation of the Mn(II)-EDTA complex with lead dioxide, can be determined by titration with standard iron(II) sulfate. 

Standard Manganese(ll) Solution. Dissolve exactly 16.901 g ACS reagent grade manganese(II) sulfate hydrate in water and dilute to 1 E. 

Another principal use of ketene is in the production of sorbic acid [110-44-1] (80,81). In this process, which requires an acidic or manganese(II) catalyst, ketene adds to crotonaldehyde [123-73-9] (8) with subsequent conversion of the P-lactone and the polyester to sorbic acid (qv) (9). 

Divalent copper, cobalt, nickel, and vanadyl ions promote chemiluminescence from the luminol—hydrogen peroxide reaction, which can be used to determine these metals to concentrations of 1—10 ppb (272,273). The light intensity is generally linear with metal concentration of 10 to 10 M range (272). Manganese(II) can also be determined when an amine is added to increase its reduction potential by stabili2ing Mn (ITT) (272). Since all of these ions are active, ion exchange must be used for deterrnination of a particular metal in mixtures (274). 

---