On the electron delocalization in the radical cations formed by oxidation of MM quadruple bonds linked by oxalate and perfluoroterephthalate bridges.

Electron paramagnetic resonance, electronic absorption, and resonance Raman spectroscopy reveal that in the oxalate-bridged compounds, [[(tBuCO2)3M2]2(mu-O2CCO2)]+[PF6]-, the unpaired electron is delocalized over four metal centers (M = Mo or W) as a result of M2 delta to bridge pi conjugation, but in the related cationic perfluoroterephthalate-bridged species, the tungsten complex is delocalized and the molybdenum analogue valence trapped.