Thermal behavior of new nickel(II) complexes with unsaturated carboxylates and heterocyclic N-donor ligands

Synthesis and characterization of four new Ni(II) complexes with mixed ligands have been reported in the present paper. As interest ligands, acrylate (acr) ion together with one N-donor heterocyclic ligand, namely benzimidazole (HBzIm), 2-methylbenzimidazole (2-MeBzIm), 5-methylbenzimidazole (5-MeBzIm) or 5,6-dimethylbenzimidazole (5,6-Me2BzIm), was chosen. The syntheses afforded the complexes formulated as [Ni(HBzIm)2(acr)2(H2O)]·3H2O (1), [Ni(2-MeBzIm)2(acr)2(H2O)]·1.5H2O (2), [Ni(5-MeBzIm)2(acr)2(H2O)] (3) and [Ni(5,6-Me2BzIm)2(acr)2] (4). Complexes (1) and (2) contain crystallization water molecules and coordinated water molecules, both their nature and presence being confirmed on the basis of IR spectra and thermal analysis. In contrast to above-mentioned complexes, (3) contains only coordinated water molecule, while (4) is an anhydrous compound. Based on electronic spectra and magnetic measurements, a distorted octahedral stereochemistry was proposed for all Ni(II) complexes. Acrylate ions act both as unidentate and chelate ligands in complexes (1)–(3), while in complex (4) act only as chelate ligands. All used N-donor ligands function as monodentate in all Ni(II) complexes. Biological properties of complexes (1)–(4) were evaluated against several Gram(+), Gram(−) bacterial strains and against fungus Candida albicans.