COORDINATION CHEMISTRY OF HIGHER OXIDATION-STATES .40. SPECTROSCOPIC, ELECTROCHEMICAL AND STRUCTURAL STUDIES OF CATIONIC OSMIUM-(III) AND OSMIUM-(IV) DIPHOSPHINE AND DIARSINE COMPLEXES

The osmium(III) complexes trans-[Os(L-L)2X2]BF4 [X = Cl or Br; L-L = o-C6H4(PMe2)2, o-C6H4(AsMe2)2, o-C6H4(AsMe2)(PMe2), o-C6F4(AsMe2)2, Ph2PCH2CH2PPh2, Me2PCH2CH2PMe2, Ph2AsCH=CHAsPh2, o-C6H4(PPh2)2 or o-C6F4(PPh2)2] have been prepared by dilute HNO3 oxidation of the osmium(II) analogues in aqueous HBF4. Concentrated HNO3 converts most of these complexes into Os(IV), but the unstable trans-[Os(L-L)2X2][ClO4]2 were isolated as solids only for L-L = o-C6H4(PMe2)2, o-C6H4(AsMe2)2 or o-C6H4(AsMe2)(PMe2). Cyclic voltammetry reveals that the Os(II)-Os(III) and Os(III)-Os(IV) couples are generally reversible. Assignments of the UV/VIS spectra of the osmium-(III) and -(IV) complexes are proposed. The X-ray structure of trans-[Os{o-C6H4(AsMe2)2}2Cl2]ClO4 is reported: monoclinic, space group C2/m, a = 13.890(2), b = 10.381(2), c = 11.682(3) angstrom, beta = 113.86(2)-degrees, Z = 2, and with R = 0.039. Osmium L(III)-edge (and where appropriate bromine K-edge) extended X-ray absorption fine structure data for the complexes trans-[Os{o-C6H4(AsMe2)2}2X2]n+ (n = 0-2) are reported and the trends in Os-As and Os-X bond lengths with changing osmium oxidation state are discussed.