Emission quantum yields observed for the dimetallic complexes [(bpy)(2)Os-II-(tppb)-M(II)(dppb)] (M = Ni, Pd, Pt) and [(bpy)(2)Os-II-(bpy)(2)] (bpy = 2,2’-bipyridine; dppb = 1,2-bis(diphenylphosphino)benzene; tppb = 1,2,4,5-tetrakis(diphenylphosphino)benzene) reflect substantial intramolecular interaction between the component metal centers in the excited states of these complexes. The slightly shifted redox potentials and absorption spectra of the dimetallic complexes, in comparison with their monometallic models, [Os-II(bpy)(2)(dppb)] and [M(II)(dppb)(2)] (M = Ni, Pd, Pt), are consistent with modest interactions in the ground states of these complexes, as has been observed for the analogous Ni-II dimetallic complexes. The quantum yields (phi = 0.002) and excited state lifetimes (tau = 9-12 ns) of the dimetallic complexes [(bpy)(2)Os-II-(tppb)-M(II)(dppb)] (M = Ni, Pd) were lower and shorter than those of [Os-II(bpy)(2)(dppb)] (phi = 0.049, tau = 270 ns), as is consistent with quenching of the Os-II MLCT state by the second metal center. The apparent intramolecular electron transfer rate constants (k(et) = 3 x 10(5)-1 x 10(8) S-1) for the excited states of the dimetallic complexes [(bpy)(2)Os-II-(tppb)-M(II)(dppb)] (M = Ni, Pd, Pt) correlate with calculated driving forces for electron transfer from *Os-II to M(II) (M = Ni, Pd, Pt).