The preparation and characterisation of some diacidorhodium(III) complexes of the type cis- and trans-[RhXY(di-phosphine)2]⁺(X or Y = Cl, Br, or H) are described. Their spectra are discussed as an aid to stereochemical assignments for these complexes. Preparation of the rhodium(I) complex, Rh(Me2P·CH2·CH2·PMe2)2Cl, and its reactions with hydrogen, carbon monoxide, halogens, hydrogen, halides, and other reagents are described.