Abstract
Standard enthalpies of formation of crystalline samples at 298.15 K were determined by solution calorimetry (oxidative hydrolysis), for ΔHf⊖[Mo2(OPri) 6, c] = -(1661.8±9) kJ mol-1 and ΔHf⊖[Mo2(OPri) 8, c] = -(2292.5±10) kJ mol-1. The dissociation process [Mo2(OPri)8, g] → 2 Mo(OPri)4, g is calculated to be endothermic, ΔH ≈ 184 kJ mol-1. A bond-enthalpy/bond-length curve is tentatively proposed for Mo-Mo bonds. A similar curve for Mo-O bonds is given, to fit the limited thermochemical data available. It is concluded that the Mo=Mo bond in Mo2(OPri)8 contributes ca. 200-230 kJ mol-1 to the binding in this molecule.