Standard enthalpies of formation of the tetra-µ-acetato-derivatives of dimolybdenum(II), chromium(II)–molybdenum(II), dichromium(II), and dichromium(II) dihydrate, and di-µ-acetato-bis(pentane-2,4-dionato)dimolybdenum(II), and their metal–metal bond enthalpy contributions

Abstract

The following standard enthalpies (kJ mol^–1) of formation of the crystalline solids at 298.15 K have been determined using solution reaction calorimetry: ΔH_t^⊖[Mo₂(O₂CMe)₄c]=–1 970.7 ± 8.4, ΔH_t^⊖[CrMo(O₂CMe)₄,c]=–2 113.9 ± 6.4, ΔH_t^⊖[Cr₂(O₂CMe)₄,c]=–2 297.5 ± 6.6, ΔH_t^⊖[Cr₂(O₂CMe)₄.2H₂O,c]=–2 875.4 ± 6.7, and ΔH_t^⊖[Mo₂(O₂CMe)₂(pd)₂,c](pd = pentane-2,4-dionate)=–1 805.0 ± 8.9. The corresponding metal–metal bond enthalpy contributions in the gaseous species have been assessed as D(Mo–Mo)= 334, D(Cr–Mo)= 249, and D(Cr–Cr)= 205 kJ mol^–1. The bond enthalpy contribution for the co-ordination of each water molecule in [Cr₂(O₂CMe)₄]·2H₂O has been estimated as 44 kJ mol^–1.