Manganese(III) phosphate complexes in 3M(Li+, H+)ClO4− media

The equilibria between Mn3+ and phosphate ions have been studied, at 25°C in 3M(Li+, H+)ClO4− media, by measuring the potential of the Mn3+Mn2+ half-cell at a series of [H+] as a function of the [H3PO4] and of the [Mn(III)]. The [H+] values ranged from 0.5 to 3M, while [Mn(III)] was varied between 5 × 10−5 and 10−3M. At each [H+] level the [H3PO4] was increased up to 0.1M. The data log [ Mn 3+ ] = ƒ([ H + ], [ H 3 PO r ]) , which indicate that only a small proportion of the reagents can be transformed into reaction products without the formation of a precipitate, may be explained with the existence of MnH2PO42+, Mn(H2PO4)2+ and of MNHPO4+, which most probably is a hydrolytic species: Mn(OH)H2PO4+. The equilibrium constants for the formation of these complexes are given.