Mixed valency and metal–metal quadruple bonds

Linking organic conjugated systems with MM quadruple bonds (M = Mo or W) allows for the study of mixed valence metal and organic centered radicals in their ground and photo-excited states. A variety of spectroscopic studies have been employed to determine the nature of the charge distribution and the classification as Class II or III on the Robin and Day scheme.

► Oxidation of a MM quadruple bond leads to a fully delocalized MV ion.
► Oxidation of linked MM quadruple bonds leads to MV ions that are characterized by a wide variety of spectroscopic methods as delocalized or localized.
► Photo-excited states of neutral complexes of MM quadruply bonded complexes have similarly been classified on the basis of femtosecond time resolved infrared spectroscopy.