Electronic coupling between molybdenum or tungsten quadruple bonds linked by dicarboxylate ligands

The preparations and structures of dicarboxylate bridged complexes having MM quadruple bonds are described where M = Mo or W. The electronic structure of these complexes is shown to be dramatically altered by M2 δ-bridge π orbital interactions. The significance of M2 δ-bridge π conjugation is revealed by electronic structure calculations employing density functional theory and is manifest in the attendant spectroscopies of these compounds (UV-vis, Raman and resonance Raman), together with electrochemical studies and the EPR spectra of the single electron oxidized radical cations.