Synthesis, electrochemistry and structural characterization of luminescent rhenium(I) monoynyl complexes and their homo- and hetero-metallic binuclear complexes

A series of luminescent rhenium(I) monoynyl complexes, [Re(NN)(CO)3(CCR)] (NN=bpy, tBu2bpy; R=C6H5, C6H4Cl-4, C6H4OCH3-4, C6H4C8H17-4, C6H4C6H5, C8H17, C4H3S, C4H2SC4H3S, C5H4N), together with their homo- and hetero-metallic binuclear complexes, {Re(NN)(CO)3(CCC5H4N)[M]} (NN=bpy, tBu2bpy; [M]=[Re{(CF3)2-bpy}(CO)3]ClO4, [Re(NO2-phen)(CO)3]ClO4, W(CO)5) have been synthesized and their electrochemical and photoluminescence behaviors determined. The structural characterization and electronic structures of selected complexes have also been studied. The luminescence origin of the rhenium(I) alkynyl complexes has been assigned as derived states of a [dπ(Re)→π*(NN)] metal-to-ligand charge transfer (MLCT) origin mixed with a [π(CCR)→π*(NN)] ligand-to-ligand charge transfer (LLCT) character. The assignments are further supported by extended Hückel molecular orbital (EHMO) calculations, which show that the LUMO mainly consists of π*(NN) character while the HOMO is dominated by the antibonding character of the ReCCR moiety resulted from the overlap of the dπ(Re) and π(CCR) orbitals.