Synthesis, structures and thermal properties of Cu(II) and Ni(II) complexes containing diethylenetriamine and nicotinate ligands

The syntheses and crystal structures of four new divalent transition metal complexes of the types [Cu2(dien)2(nic)](ClO4)3 · MeOH (nic = anion of nicotinic acid; dien = diethylenetriamine), 1; [Cu(dien)(nic)]2(nic)2, 2; [Cu(dien)(nic)]2(BF4)2 · 2MeOH, 3 and [Ni(dien)(nic)(H2O)]4(NO3)4 · 2MeOH, 4, are reported, which were prepared by the reactions of diethylenetriamine and nicotinic acid with Cu(ClO4)2 · 6H2O, Cu(OAc)2 · H2O, Cu(BF4)2 · 6H2O and Ni(NO3)2 · 6H2O in MeOH, respectively. These complexes were characterized by single-crystal X-ray diffraction method and elemental analyses. In the cation of complex 1, one nicotinate ligand bridges two Cu(II) metal centers through the pyridyl nitrogen atom and one of the carboxylate oxygen atoms. The cations of complexes 2 and 3 form the twelve-membered metallocycles, involving two Cu(II) ions that are bridged by two nicotinate ligands. The cation of complex 4 forms a tetranuclear cage with the four Ni(II) metal centers bridged by four nicotinate ligands and each Ni(II) metal center adopts the distorted octahedral geometry. Their thermal properties have been investigated by using differential scanning calorimetry (DSC) and thermogravimetric analyses (TGA).