The standard molar enthalpies of acid-base reactions in the condensed state (Delta,H-o) of the adducts MX(2) . nBuL (where M is Zn, Cd, Hg; X is Cl, Br, I; n=1, 2, 3; BuL is 2-pyrrolidone) were determined from enthalpies of dissolution (Delta(i)H(o)) of metal halide ligands and adducts, at 298.15 K, obtained by calorimetric methods in solution. Using the values of Delta(r)H(o) and auxiliary data from the literature the standard enthalpies of formation (Delta(f)H(o)), decomposition (Delta(d)H(o)) and lattice enthalpy (Delta(latt)H(o)) of these adducts were determined. The enthalpy of vaporization of BuL, Delta(vap)H(o)(BuL), was found to be 41.71 +/- 0.56 kJ mol(-1) and, from this value, the enthalpies of reaction in the gaseous state (Delta(g)H(o)) were estimated. The values of Delta(g)H(o) were used in calculations of the mean dissociation enthalpy of the metal-oxygen bond, ($) over bar D(M-O), of the obtained adducts, and are correlated with energetic parameters of the metal halides.