On the electron delocalization in the radical cations formed by oxidation of MM quadruple bonds linked by oxalate and perfluoroterephthalate bridgesElectronic Supplementary Information (ESI) available: experimental procedures; details of instrumentation; electronic absorption spectra of Mo2(O2CtBu)4+ and Mo4OXA+; tabulation of selected Raman data. See http://www.rsc.org/suppdata/cc/b2/b202344j/Dedicated to Prof. Dr Walter Siebert on the occasion of his retirement

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