Ligand-bridged homo- and hetero-binuclear carbonyl polypyridyl complexes of ReI: syntheses, electronic spectra, redox, and luminescence behaviour

Abstract

Electronic absorption data, redox potentials, and photophysical properties are reported for a series of mono- and ligand-bridged bi-nuclear carbonyl polypyridyl complexes of Re^I: [{ReCl(CO)₃}_nL^b] and [(OC)₃ClRe(L^b)M(bipy)₂]²⁺[bridging ligand (L^b)= 2,3-bis(2′-pyridyl)pyrazine (dpp) or 2,3-bis(2′-pyridyl) quinoxaline(dpq); bipy = 2,2′-bipyridine; M = Ru^II or Os^II; n= 1 or 2]. For all the binuclear complexes examined, electronic absorption and electrochemical data indicate extensive stabilization of the ligand π* orbital upon binucleation. These are also the first cases of strongly coupled ligand-bridged dimeric complexes of Re^I that exhibit luminescence (charge-transfer type) in solution at room temperature. Data on the emission maxima and lifetimes of heterobinuclear complexes of Re and Ru confirm earlier indications that the emitting state is essentially localized on the Ru→L^b charge transfer.