Rhenium-based molecular rectangles as frameworks for ligand-centered mixed valency and optical electron transfer

A series of six neutral, tetrametallic, molecular rectangles are synthesized that have the form ([Re(CO)3]2BiBzlm)2-Mu,Mu'-(LL)2, where BiBzlm is 2,2'-bisbenzimidazolate and LL is reducible, dipyridyl or diazine ligand. The X-ray crystallography and computational modeling shows that the observed differences largely reflect detailed geometric configurational differences that can either facilitate or frustrate productive direct orbital overlap.