Mix and (Mis)match: further studies of the electronic structure and mixed-valence characteristics of 1,4-diethynylbenzene-bridged bimetallic complexes

摘要

The 1,4-diethynylbenzene motif is commonly employed as a bridging ligand in bimetallic molecular systems intended to show pronounced intramolecular electronic interactions, delocalized electronic structures and 'wire-like' properties between the metal fragments at the ligand termini. In contrast to these expectations, the donor-acceptor compounds [{Cp'(CO)(x)M'}(mu-CuCC6H4C=C){M(PP)Cp'}](n+) [n = 0, 1; M'(CO)(x)Cp' = Fe(CO)(2)Cp, W(CO)(3)Cp*; M(PP)Cp' = Fe(dppe)Cp, Fe(dppe)Cp*, Ru(PPh3)(2)Cp, Ru(dppe)Cp, Ru(dppe)Cp*] display remarkably little bridge-mediated electronic interaction between the electron-rich {M(PP)Cp'} and electron-poor {M'(CO)(x)Cp'} fragments in the ground state. However, a relatively high-energy (26 000-30 000 cm(-1)) M-to-M' charge transfer can be identified. One-electron oxidation is largely localized on the {M CuCR)(PP)Cp'} fragment and gives rise to a new charge transfer band with bridging-ligand-to-{M(PP)Cp'}+ (M'(CO)(x)Cp' = Fe(CO)(2)Cp) or M'-to-M(+) (M(CO)(x)Cp' = W(CO)(3)Cp*) character. The localized electronic ground state of these complexes is better revealed through analysis of the IR spectra, taking advantage of the well-resolved nu(C C) and nu(CO) bands and IR spectroelectrochemical methods, than through the more classical analysis based on the concepts of Marcus-Hush theory and analysis of the putative IVCT electronic transition. The conclusions are supported by DFT calculations using the BLYP35 functional.