structural:summarization, structural:scholar_edition
Chemical compounds

Common oxidation states of manganese are +2, +3, +4, +6, and +7, although all oxidation states from −3 to +7 except –2 have been observed. Manganese in oxidation state +7 is represented by salts of the intensely purple permanganate anion MnO − 4. Potassium permanganate is a commonly used laboratory reagent because of its oxidizing properties; it is used as a topical medicine (for example, in the treatment of fish diseases). Solutions of potassium permanganate were among the first stains and fixatives to be used in the preparation of biological cells and tissues for electron microscopy.

Aside from various permanganate salts, Mn(VII) is represented by the unstable, volatile derivative Mn O. Oxyhalides (MnO F and MnO Cl) are powerful oxidizing agents. The most prominent example of Mn in the +6 oxidation state is the green anion manganate,. Manganate salts are intermediates in the extraction of manganese from its ores. Compounds with oxidation states +5 are somewhat elusive, and often found associated to an oxide (O) or nitride (N) ligand. One example is the blue anion hypomanganate.

Mn(IV) is somewhat enigmatic because it is common in nature but far rarer in synthetic chemistry. The most common Mn ore, pyrolusite, is MnO. It is the dark brown pigment of many cave drawings but is also a common ingredient in dry cell batteries. Complexes of Mn(IV) are well known, but they require elaborate ligands. Mn(IV)-OH complexes are an intermediate in some enzymes, including the oxygen evolving center (OEC) in plants.

Simple derivatives Mn are rarely encountered but can be stabilized by suitably basic ligands. Manganese(III) acetate is an oxidant useful in organic synthesis. Solid compounds of manganese(III) are characterized by its strong purple-red color and a preference for distorted octahedral coordination resulting from the Jahn-Teller effect.

A particularly common oxidation state for manganese in aqueous solution is +2, which has a pale pink color. Many manganese(II) compounds are known, such as the aquo complexes derived from manganese(II) sulfate (MnSO) and manganese(II) chloride (MnCl). This oxidation state is also seen in the mineral rhodochrosite (manganese(II) carbonate). Manganese(II) commonly exists with a high spin, S = 5/2 ground state because of the high pairing energy for manganese(II). There are no spin-allowed d–d transitions in manganese(II), which explain its faint color.