Enthalpies of formation of hexakis(isopropoxy)-dimolybdenum and octakis-(isopropoxy)-dimolybdenum and the metal–metal bond enthalpy contributions
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 MoMo bond in Mo2(OPri)8 contributes ca. 200–230 kJ mol–1 to the binding in this molecule.