The compounds [M(pd)(2)(L)] (where M is manganese(II) or copper(II); pd is pentane-2,4-dionate; and L is piperazine (pipz), 4-cyanopyridine (4-cyanopy), quinoline (quin) or 2,2'-bipyridine (bipy)) were synthesized and characterized by elemental analysis, melting points, thermal studies and electronic and IR spectroscopy. The enthalpies of dissolution of adducts, metal pentane-2,4-dionate and ligands in a 1:3 (v/v) mixture of aqueous HCl 1.2 M and 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 reaction in the gaseous phase (Delta(r)H(theta)(g)). The mean standard bond dissociation enthalpies of the manganese-nitrogen and copper-nitrogen bonds have been determined.