C- and Z-shaped coordination compounds. Synthesis, structure, and spectroelectrochemistry of cis- and trans-[Re(CO)₃(L)] ₂-2,2′-bisbenzimidizolate with L = 4-phenylpyridine, 2,4′-bipyridine, or pyridine

A series of C- and Z-shaped complexes of the form cis- and trans-[Re(CO)₃(L)]₂BiBzIm, where L = 4-phenylpyridine, 2,4′-bipyridine, or pyridine and BiBzIm = 2,2′-bisbenzimidizolate, have been synthesized by the reaction of [Re(CO)₄]₂BiBzIm with a slight excess of L in refluxing tetrahydrofuran. Five of the six compounds have been isolated and crystallographically and electrochemically characterized. Formation of the sixth, the cis form of the [Re(CO) ₃(4-phenylpyridine)]₂BiBzIm, is evidently inhibited by the torsional steric demands of proximal 4-phenylpyridines. The compounds are acyclic analogues of recently studied tetrarhenium molecular rectangles and are of interest, in part, because of their potential to form ligand-centered mixed-valence (LCMV) compounds upon reduction by one electron. Spectroelectrochemical measurements corroborated the formation of a LCMV version of cis-[Re(CO)₃(L)]₂BiBzIm but failed to uncover a ligand-based intervalence transition. Electrochemical measurements revealed isomer-dependent L/L electrostatic effects, resulting in greater mixed-valence ion comproportionation for C-shaped assemblies versus Z-shaped assemblies.