Standard enthalpies of formation of tris[bis(pentane-2,4-dionato)nickel(II)] and bis(2,2,6,6-tetramethylheptane-3,5-dionato)nickel(II) and an estimation of nickel–oxygen bond energies

Abstract

Standard enthalpies of formation of the title complexes have been determined from hydrolyses in acid solution by solution calorimetry at 298.15 K as –624.0 ± 2.2 and –299.2 ± 2.0 kcal mol^–l respectively. Estimates of gas-phase enthalpies of the monomeric forms of both complexes yield an average homolytic Ni–O bond energy of 50 ± 2 kcal mol^–l, but in the pentane-2,4-dionate trimer the bridging oxygens have Ni–O bond energies of approximately half those of the terminal Ni–O bonds.