Manganese oxidation states, aqueous solution

Hydrated manganese in acidic aqueous solution exists in two oxidation states, Mn11 and Mnm, with a potential of +1.51 volts separating them (339). Therefore, Mn"1 in solution is a strong oxidant. This... 

The chemistry of technetium(II) and rhenium(II) is meagre and mainly confined to arsine and phosphine complexes. The best known of these are [MCl2(diars)2], obtained by reduction with hypophosphite and Sn respectively from the corresponding Tc and Re complexes, and in which the low oxidation state is presumably stabilized by n donation to the ligands. This oxidation state, however, is really best typified by manganese for which it is the most thoroughly studied and, in aqueous solution, by far the most... 

Manganese represents the epitome of that characteristic property of the transition element namely the variable oxidation state. The aqueous solution chemistry includes all oxidation states from Mn(II) to Mn(VII), although these are of varying stability. Recently attention has been focused on polynuclear manganese complexes as models for the cluster of four manganese atoms which in conjunction with the donor side of Photosystem(II) is believed involved in plant photosynthetic oxidation of water. The Mn4 aggregate cycles between 6 distinct oxidation levels involving Mn(II) to Mn(IV). 

A small number of salts of tripositive manganese are known in the solid state (for example, MnF3, Mn2(S04)s, and Mn(OAc)s). Each of these salts is hydrolyzed to Mn203 on treatment with water. If dissolved in acid, they disproportionate to M11O2 and MnH. Thus, in aqueous solution, Mn(III) may exist only in complexed form. Such complexes are generally prepared by oxidation of the corresponding complex of Mn(II) ... 

The aqua ion can be obtained by electrolytic or peroxosulfate oxidation of Mn2+ solutions, or by reduction of Mn04. The ion plays a central role in the complex redox reactions of the higher oxidation states of manganese in aqueous solutions. It is most stable in acid solutions, since it is very readily hydrolyzed ... 

This is the dominant oxidation state and the most stable. In neutral or acidic aqueous solution, very pale pink [Mn(H20)6] + is present, which is resistant to oxidation, while in basic media, the hydroxide Mn(OH)2 formed is easily oxidized by air (Figure 1). Manganese (II) is a hard acid and is quite distinctly a class (a) metal. This is manifest, for example, in the preference for O donors rather than N-donor... 

Manganese can exist in all oxidation states from +2 to +7, although +2 and +7 are the most common. Manganese(II) forms an extensive series of salts with all the common anions. In aqueous solution Mn2+ forms Mn(H20)s2+, which has a light pink color. Manganese(VII) is found in the intensely purple permanganate ion (Mn04 ). Widely used as an analytical... 

For an element exhibiting several different oxidation states in aqueous solution, we must consider a number of different half-reactions in order to obtain a clear picture of its solution chemistry. Consider manganese as an example aqueous solution species may contain manganese in oxidation states ranging from Mn(II) to Mn(VII), and equations 7.42-7.46 give half-reactions for which standard reduction potentials can be determined experimentally. 

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