METAL-METAL COUPLING ELEMENTS OF MIXED-VALENCE PENTAAMMINERUTHENIUM DIMERS - THE HOLE-TRANSFER SUPEREXCHANGE CASE

The extent of metal-metal coupling in the mixed-valence complexes [{Ru (NH3)(5)}(2)(mu-L)](3+)], where L is 2,5-dimethyl-(Me(2)dicyd(2-)), 2, 5-dichloro- (Cl(2)dicyd(2-)), 2,3,5,6-tetrachloro- (Cl(4)dicyd(2-)) or unsubstituted (dicyd(2-)) 1,4-dicyanamidobenzene dianion, was evaluat ed by comparing theoretical values of metal-metal coupling elements wi th estimates of the free energy of resonance exchange which were deriv ed from the free energies of comproportionation. Poor agreement was fo und with the Hush model; however, an excellent correlation was seen wi th the model of Creutz, Newton and Sutin (CNS). It would appear that t he CNS model is remarkably successful in describing the extent of meta l-metal coupling for the strongly coupled valence trapped complexes of this study. (C) 1997 Elsevier Science B.V.