Energetics of metal–ligand binding in copper(II) and nickel(II) complexes of two Schiff bases

Abstract

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.