CHARGE-DISTRIBUTION IN BIS(QUINONE) COMPLEXES OF RUTHENIUM AND OSMIUM - STRUCTURAL, SPECTRAL, AND ELECTROCHEMICAL PROPERTIES OF THE OS(BPY)(CAT)2 (CAT = CATECHOLATE, 3,5-DI-TERT-BUTYLCATECHOLATE, TETRACHLOROCATECHOLATE) SERIES

The series of bis(catecholato)(bipyridine)osmium(IV) complexes have been prepared by treating Os(bpy)Cl3 with either catechol, 3,5-di-tert-butylcatechol, or tetrachlorocatechol in the presence of base. Crystals of Os(bpy)(Cl4Cat)2.2C6H6 form in the monoclinic crystal system, space group P2(1)/n, in a unit cell of dimensions a = 10.906 (1) angstrom, b = 19.395 (5) angstrom, c = 16.953 (4) angstrom, beta = 91.23 (1)-degrees, and V = 3585 (1) angstrom 3, for Z = 4. The complex molecule is octahedral with chelated bpy and Cl4Cat ligands. Bond lengths to the metal and C-O lengths of the quinone ligands agree with the bis(catecholato)osmium(IV) charge distribution for the complex in solid state. Electrochemistry and UV-vis-near-IR spectra on the series suggest that in solution the charge distribution is similar to other members of the M(bpy)(Q)2 and M(PPh3)2(Q)2 series, with M = Ru, Os and Q = DBQ, Cl4Q. The five-membered redox series of these complexes show variations in potential with metal, counterligand, and quinone that permit assignment of couples as associated with metal, quinone, or metal-quinone delocalized electronic levels. Metal ion charge appears to remain relatively constant through the series ML2(Q)2n, with n ranging from +2 to -2, to the final reduction step which corresponds to a M(III)/M(II) reduction. Extreme members of the redox series have well-defined charge distributions as M(II)L2(Cat)2(2-) and M(III)L2(BQ)(SQ)2+ species. Neutral forms of the complexes have variable charge distributions in the solid state but have similar properties in solution as delocalized M(III)L2(SQ)(Cat) species.