275ChemInform Abstract The properties of the bimetallic complexes, where the only variation is the energy of the bridging ligand's π system, are studied. The lowest energy electronic absorption band is assigned as a MLCT process, where the acceptor state is localized primarily on the bridging ligand. Unlike the Ru complexes analogous to (IVa) and (IVb), the bimetallic Re containing complexes show no luminescence. The complexes (III) and (IV) display two reductions and one oxidation. The second reduction may be due to a metal-centered Re(I)/Re(0) process for (IIIa) and ligand centered for (IIIb) and (IIIc). A third reduction is observed for (IVa) and (IVb). A comparison with the analogous Ru complexes show that the Re(CO)3Cl moiety is more effective in stabilizing the reduced forms of the heterocyclic ligands than (Ru(bipy)2)2+ (yields not given).

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The nonradiative (k,J decay rates of the low-lying, emissive metal-to-ligand charge-transfer (MLCT) excited states of a series of complexes of the type [Re(dpp)(CO),L]+ (dpp = 2,3-di-2-pyridylpyrazine; L = CI-, N-methylimidazole, pyridine, 4-phenylpyridine, 4-methylpyridine, trimethylphosphine, acetonitrile) have been investigated. The results show that the "energy gap law" for radiationless decay in the weak coupling limit is obeyed by this series of complexes. The complexes yield a In k,, vs E,, plot with a slope and intercept within experimental error for two separate studies on the series where the acceptor ligand is 2,2'-bipyridine. This is taken as evidence that dpp and bpy differ only in the relative energies of the acceptor orbitals and are vibrationally similar.

The properties of the bimetallic complexes, where the only variation is the energy of the bridging ligand's π system, are studied.