Thermodynamics of metal-ligand bond formation. V. Adducts of mercury(II) halides with Lewis bases

Abstract

Thermodynamic data have been obtained for the reactions of mercury(II) halides with Lewis bases in benzene solution at 30°C. With tributyl- and triphenyl-phosphines 1 : 1 and 2 : 1 adducts were observed in solution, the 1 : 1 adduct with tributylphosphine being associated. With tetrahydrofuran, tributylamine, pyridine, 2-methylpyridine, 4- methylpyridine, tetrahydrothiophen, and triphenylarsine only 1 : 1 adducts were observed in solution, monomeric and three-coordinate, except for HgI₂AsPh₃, which probably associates to some extent. In most cases the enthalpies of formation of 1 : 1 adducts in solution are about -70 kJ mol^-1; lower enthalpies of formation of the tributylamine adducts, about -40 kJ mol^-1, are attributed to the absence of π-bonding and much lower enthalpies of formation of tetrahydrofuran adducts to the ?B character? of mercury. Wide variations in the stabilities of the adducts are mainly due to entropy effects, probably arising from differences in the solvation of the adducts.