Manganese oxoanions

The lower oxides of manganese are basic and react with aqueous acids to give salts of Mn and Mn cations. The higher oxides, on the other hand, are acidic and react with alkalis to yield oxoanion salts, but the polymerization which was such a feature of the chemistry of the preceding group is absent here. 

The distinction between the first member of the group and the two heavier members, which was seen to be so sharp in the early groups of transition metals, is much less obvious here. The only unsubstituted, discrete oxoanions of the heavier pair of metals are the tetrahedral [Ru 04] and [Ru 04]. This behaviour is akin to that of iron or, even more, to that of manganese, whereas in the osmium analogues the metal always increases its coordination number by the attachment of extra OH ions. If RUO4 is dissolved in cold dilute KOH, or aqueous K2RUO4 is oxidized by chlorine, virtually black crystals of K[Ru 04] ( permthenate ) are deposited. These are unstable unless dried and are reduced by water, especially if alkaline, to the orange... 

Pankaj, Chauhan (2004) Sonochemical studies of aqueous solutions of chromium and manganese in their cationic and oxoanionic states. Ind J Chem 43(A) 1206-1209... 

These two metals form oxoanions similar to those of manganese and rhenium. 

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