Thermodynamics of metal-ligand bond formation. XXV. Addition of bases to Bis[O,O'-diethyl thiomalonato]nickel(II) in various solvents

Abstract

Thermodynamic data have been obtained from spectroscopic and calorimetric measurements for the addition of pyridine and 4- methylpyridine to bis(O,O?-diethyl thiomalonato)nickel(II), Ni(etm)₂, in solution in cyclohexane, benzene, 1,2-dichloroethane, acetonitrile, butan-2-one and carbon tetra-chloride. In each solvent two base molecules add successively, giving Ni(etm)₂B then Ni(etm)₂B₂. There are only small variations in K₁ and K₂ in different solvents; typically K₁ ≈ 200, K₂ ≈ 100 l. mol^-1, ΔH°₁₊₂ ≈ -65, ΔH°₂ ≈ 0 kJ mol^-1 at 30°C, but in benzene and cyclohexane ΔH°₂ ≈ -25 and in cyclohexane ΔH°₁₊₂ ≈ -100 kJ mol^-1. The main driving force for adduct formation is apparently the formation of the first Ni-N bond, which is accompanied by a spin change.