Isolation of a Quadrivalent Rhodium Complex

Abstract

The only compound of quadrivalent rhodium described in the literature is the green, hydrated oxide obtained in the impure form by passing chlorine into a solution of sodium hexachlor-rhodate(III), (Na₃RhCl₆), containing excess sodium hydroxide¹. Grube and Gu² obtained greenish-violet coloured solutions by oxidizing anodically rhodium salts in sulphuric, nitric and perchloric acids. Although no solid products were isolated, the authors deduced from potentio-metric titrations that these solutions contained some quadrivalent and hexavalent rhodium. The redox potential of the trivalent-quadrivalent couple was estimated at + 1·40 volts.