STRONG METAL-METAL COUPLING IN A DINUCLEAR (TERPYRIDINE)(BIPYRIDINE)RUTHENIUM MIXED-VALENCE COMPLEX INCORPORATING THE BRIDGING LIGAND 1,4-DICYANAMIDOBENZENE DIANION

The complex, [{Ru(terpy)(bpy)}2(mu-dicyd)][PF6](2), where terpy = 2,2' ,2''-terpyridine, bpy = 2,2'-bipyridine, and dicyd(2-) = 1,4-dicyanami dobenzene dianion, has been synthesized and characterized by cyclic vo ltammetry and spectroelectrochemical methods. A quantitative absorptio n spectrum of the radical anion dicyd(.-) has also been determined. Th e mixed valence ion, [{Ru(terpy)(bpy)](2)(mu-dicyd)](3+) is strongly c oupled with K-c = 2.7 x 10(7) and has an intervalence band at lambda = 1090 nm (epsilon(max) 3000 M(-1) cm(-1), <(nu)over bar>(1/2) = 1800 c m(-1)). The mixed-valence properties of this complex were compared to its ammine analogue [{(NH3)(5)Ru}(2)(mu-dicyd)](3+) and rationalized b y the perturbation of spectator ligands on the interaction of rutheniu m ions with the dicyd(2-) superexchange pathway. The dependence of int ervalence oscillator strength on the nature of the mixed-valence compl ex was also discussed.