Synthesis, crystal structure, theoretical calculations and thermal characterization of two heterodinuclear NiII–ZnII complexes prepared from ONNO-type symmetrical Schiff base and its reduced derivative

Abstract

Two complexes in NiII–ZnII heterodinuclear form were prepared in DMF medium by the use of an ONNO-type symmetrical Schiff base bis-N,N′(salicylidene)-1,3-diaminopropane (LH2) and the reduced derivative of this ligand bis-N,N′(2-hydroxybenzylidene)-1,3-diaminopropane (LHH2). The fact that the complexes are in [NiL·ZnCl2·DMF2] and [NiLH·ZnCl2·(DMF)2] stoichiometry was verified with elemental and thermogravimetric analyses and IR spectroscopy. The structures of the complexes were determined by the use of X-ray diffraction. The two complexes were very similar, almost isostructure, and it was observed that Ni(II) ions in both complexes coordinated with two phenolic oxygens and two iminic nitrogen of organic ligand and formed an octahedral coordination between two DMF molecules. On the other hand, the Zn(II) ion was observed to be located in a tetrahedral coordination sphere coordinated with two phenolic oxygens between two halides. Although the molecular structures of the complexes are very similar, their thermal properties are quite different from of each other. The decomposition of [NiL·ZnCl2·(DMF)2] was observed between 140 and 190 °C by the removal of coordinative DMF molecules, leaving a residue of a mixture of NiL and ZnCl2 behind. The complex of the reduced ligand [NiLH·ZnCl2·(DMF)2] was observed to be stable up to 250 °C. After this temperature, the coordinative DMF molecules rapidly leave the structure before the degradation of NiLH. That is why the activation energies of the thermal reactions were evaluated by the use of isothermal and nonisothermal kinetic models: Coats–Redfern, Ozawa, Ozawa–Flynn–Wall and Kissinger–Akahira–Sunose. Also the thermal differences between these two complexes were examined by the use of theoretical programs included in Gaussian 09 package. The ground-state energies calculations were carried out by the use of density functional theory method 631G(d) basis set. The calculated theoretical bond energies and angles were observed to be different compared with the experimental data. The HOMO and LUMO values of the complexes were also calculated. The difference between these two complexes was evaluated.