Oxalate bridged heteronuclear compounds containing MM quadruple bonds (M = Mo and W) and their radical cations

The heteronuclear MM quadruply bonded oxalate bridged compound [(t-BuCO2)3MoW]2(µ-C2O4) (I) has been prepared from the reaction between MoW(O2Ct-Bu)4 and oxalic acid and characterized by elemental analysis, 1H NMR and UV-vis spectroscopy, and electrochemical studies. Single electron oxidation of I by reaction with Ag+PF6– leads to the formation of the kinetically labile radical cation I+, which has been characterized by UV-vis, NIR, and EPR spectroscopy. The latter results are compared with the properties of their related homonuclear Mo4- and W4-oxalate bridged compounds and their respective radical cations. The spectroscopic features of the related radical cations [(t-BuCO2)6MoxWy(µ-C2O4)]+, where x = 1, 2, 3 and y = 4 – x, are also described with the conclusion that the [(t-BuCO2)3Mo2(µ-C2O4)W2(O2Ct-Bu)3]+ and [(t-BuCO2)3Mo2(µ-C2O4)MoW (O2Ct-Bu)3]+ cations are valence trapped on the Robin and Day scheme for the classification of mixed valence compounds.Key words: molybdenum, tungsten, mixed valence.