COMPARATIVE-STUDIES ON CHARGE-DISTRIBUTION FOR THE RUTHENIUM AND OSMIUM QUINONE COMPLEXES [M(BPY)2(QUINONE)]N (M = RU, OS, N = 0, +1, +2)

The apparent shift in charge distribution that occurs for quinone complexes of metals of the iron triad has been investigated for members of the M(bpy)2(Q)n(M = Ru, Os) redox series for values of n ranging from 0 to +2 and for complexes prepared with catechol (Cat), 3,5-di-feri-butylcatechol (DBCat), and tetrachlorocatechol (Cl4Cat). The members of the series with n = +1 may have one of two localized charge distributions, M(II)-SQ or M(III)-Cat, related by internal transfer of charge between the metal and the quinone ligand. Earlier characterization on Ru(bpy)2(DBSQ)+indicated that the semiquinone form was most appropriate on the basis of the spectroscopy and structure of the complex cation. The osmium analogue, [Os(bpy)2(DBCat)](C104), has been the subject of a crystallographic structure determination. Crystals of the complex form in the monoclinic space group P21/c with Z = 4 in a unit cell of dimensions α = 15.265 (3) Å, b = 24.153 (6) Å, c = 10.944 (2) Å and β = 102.89 (2)°. Carbon-oxygen bond lengths of the structure indicate that the quinone ligand is catecholate and that the charge distribution for the complex is Os(lII)-DBCat. Spectroscopic characterization on the complex confirms the trivalent nature of the metal. It exhibits a rhombic EPR spectrum and low-energy transitions in the near-infrared region that are characteristic of Os(III). A comparative study on the electrochemical properlies of the six complexes prepared with the two metals and three quinone ligands fails to show shifts in redox potentials that would be expected for species with metal- and ligand-localized electronic structures. This result, with earlier characterization on the Ru members of the series, points to significant metal-quinone charge derealization for certain members of the series. © 1990, American Chemical Society. All rights reserved.