Molecular thermochemical study of Ni(II), Cu(II) and Zn(II) complexes with N,N′-bis(salicylaldehydo)ethylenediamine

The standard (p(0) = 0.1 MPa) molar enthalpies of formation, at T= 298.15 K, of crystalline Ni(II), Cu(II) and Zn(II) complexes with N,N'-bis(salicylaldehydo)ethylenediamine (H(2)salen) were determined by solution-reaction calorimetry measurements as, respectively. Delta(f)H(m)(-) {[Ni(salen)], cr}=-(226.1 +/- 3.9)kJmol(-1), DeltafH(m)(o) {[Cu(salen)], cr}=-(139.0 +/- 3.9)kJmol(-1) and Delta(f)H(m)(o) {[Zn(salen)], cr}=-(281.3 +/- 4.6)kJmol(-1). The standard molar enthalpies of sublimation of the same metal complexes, at T=298.15K, were obtained by effusion methods as Delta(cr)(g)H(m)(o), [Ni(salen)]=(163.9+/-3.2)kJmol(-1), Delta(cr)(g)H(m)(o) [Cu(salen)]=(175.3 +/- 2.7)kJmol(-1) and Delta(g)(cr)H(m)(o) [Zn(salen)]=(179.6 +/- 3.7)kJmol(-1). The differences between the mean metal-ligand and hydrogen-ligand bond dissociation enthalpies were derived and discussed in terms of structure, in comparison with identical parameters for complexes of the same metals with other tetradentate Schiff bases involving a N2O2 donor set. (C) 2004 Elsevier B.V. All rights reserved.