Thermodynamics of metal-ligand bond formation. VI. Trimerization and base addition of nickel(II) β-diketonates

Abstract

Five nickel(II) complexes of β-diketones (LH) have been studied by calorimetric titration with pyridine in benzene solution. Trimerization of the complexes NiL₂ is endothermic and entropy-driven, probably as a result of desolvation of the low-spin monomers. Reaction with pyridine occurs in two steps, forming successively Ni₂L₄(py) and NiL₂(py)₂. The enthalpy of formation of NiL₂(py)₂ from the intermediate adduct is about -40 kJ mol^-1 and shows no evidence for bulkiness of the ligand leading to steric instability in Ni₂L₄(py). Variations in the relative stabilities of the monomeric and trimeric forms of NiL₂ seem more likely to be due to electronic than steric effects.