Enthalpy of sublimation of adducts—an evaluation involving MX 2· nL (M = Zn, Cd, Hg; X = Cl, Br, I; n = 1, 2, 3; L = organic base containing CO or PO groups) adducts

Abstract

The approximation that the molar enthalpy of sublimation of an adduct is equal to the molar enthalpy of sublimation or vaporization of the ligand, has been applied to the calculation of the mean enthalpy of dissociation of the metal-ligand bond, D (MO), for adducts of the type MX 2· nL (M = Zn, Cd, Hg; X = Cl, Br, I; n = 1, 2, 3; L = ligand containing PO or CO groups) and for other similar compounds. Based on a thermochemical cycle, a linear equation D (MO) = AΔ r H(a) + B was obtained, with A = 1/ n and Δ r H(a) derived from the enthalpy of the reaction MX 2· nL(s) = MX 2(g)+ nL(g), whose thermochemical value was calculated from experimental data. By using data from nearly 80 compounds and calculating D (MO) for various approximations, it was verified through linear regression that the cited approximation is the one which correlates the best with the stoichiometries of the compounds. This result is a good argument for the use of this approximation in D (MO) calculations.