The compounds Ni(AcAc)(2).nL (where AcAc is acetylacetonate; L piperazine (pipz), morpholine (morph), piperidine (pipd), pyridine (py), 3-methylpyridine (beta-pico), 4-methylpyridine (gamma-pico), 3-cyanopyridine (3-cyanopy), 4-cyanopyridine (4-cyanopy), 2,2'-bipiridine (bipy) or quinoline (quin), and n=1 or 2) were synthesized and characterized by elemental analysis, melting points, thermal studies and electronic and IR spectroscopy. The enthalpies of dissolution of adducts, Ni(II) chelate and ligands in 25% (v/v) aqueous HCl 1.2 N in methanol were measured and, by using thermochemical cycles, the following thermochemical parameters for the adducts have been determined : The standard enthalpies for the Lewis acid/base reaction (Delta(r)H(theta)) the standard enthalpies of formation (Delta(f)H(theta)); the standard enthalpies of decomposition (Delta(D)H(theta)), the lattice standard enthalpies (Delta(M)H(theta)) and the standard enthalpies of the Lewis acid/base reactions in the gaseous phase (Delta(r)H(theta)(g)). The mean standard enthalpies of the nickel-nitrogen bonds have been estimated.