The standard molar enthalpies of formation, at 298.15 K, of crystalline copper(II) and nickel(II) complexes with 4,4′-ethylenedinitrilobis(pentan-2-one) (H 2 acacen) and with 1,1′-diphenyl-3,3′-ethylenedinitrilobis(butan-1-one) (H 2 bzacen), were determined from solution-reaction calorimetric measurements as, respectively, Δ f H° m [Cu(acacen), cr] = -385.1 ± 3.2, Δ f H° m [Cu(bzacen), cr] = - 203.4 ± 5.1, Δ f H° m [Ni(acacen), cr] = -472.6 ± 3.1 and Δ f H° m [Ni(bzacen), cr] = -292.2 ± 5.1 kJ mol -1 . The standard molar enthalpies of sublimation of the same metal complexes, at 298.15 K, were obtained by effusion methods as: Δ c g r H° m [Cu(acacen) = 127.6 ± 0.7, Δ c g r H° m [Ni(acacen)] = 129.1 ± 0.9, Δ c g r H° m [Cu(bzacen)] = 205.6 ± 3.0 and Δ c g r H° m [Ni(bzacen) = 201.7 ± 2.8 kJ mol -1 . The differences between the mean metal–ligand and hydrogen–ligand bond-dissociation enthalpies were derived.