Twists and turns: Studies of the complexes and properties of bimetallic complexes featuring phenylene ethynylene and related bridging ligands

摘要

The concept of a molecular-based electronic technology has been evolving for over 50 years, and the development of molecular designs for such components over this period has drawn heavily on studies of intramolecular charge transfer in mixed-valence complexes and related systems. Recent advances in methods for the assembly and measurement of device characteristics of metal|molecule|metal junctions have brought the realisation of the considerable promise of the area within a tantalisingly close reach. This review presents a selective summary of the chemistry, spectroscopic properties and electronic structures of bimetallic complexes [{L_xM}(μ-bridge){MI_x}]~(n+) based primarily, but not exclusively, on the Ru(PP)Cp' and Mo(dppe)(η-C_7H_7) fragments and alkynyl based bridging ligands. The molecular design strategies that lead to a wide spectrum of electronic characteristics in these systems are described. Examples range from weakly coupled mixed-valance complexes through more strongly coupled systems in which the electronic states of the bridging ligand are intimately involved in electron transfer processes to complexes. An argument is made that the latter are better described in terms of redox non-innocent bridging ligands supported by metal-based donor substituents rather than strongly coupled mixed-valence complexes. The significance of these results on the further development of metal complexes for use as components within a hybrid molecular electronics technology are discussed.