Heteroleptic Ni(II) complexes containing chelating benzoato ligand with sharp bite angle: syntheses, crystal structures, and magnetism

From the system Ni(OH)2 - 4,4 '-dmbpy - HBz (HBz = benzoic acid; 4,4 '-dmbpy = 4,4 '-dimethyl-2,2 '-bipyridine) under various experimental conditions three complexes were isolated, namely light blue [Ni(4,4 '-dmbpy) (Bz)2(H2O)] (1), violet [Ni(4,4 '-dmbpy)2(Bz)](Bz)& sdot;2HBz (2), and pink microcrystalline product [Ni(4,4 '-dmbpy)3] (Bz)2 & sdot;3.5H2O (3). The crystal structures of 1 and 2 were determined, that of 2 at two temperatures (100 and 277 K). The crystal structure of 1 is formed of neutral molecules, in which the Ni(II) central atom is hexa-coordinated by one chelating diamine ligand, one chelating and one monodentate benzoato ligands, and one aqua ligand. The crystal structure of 2 is ionic and in the complex cation the Ni(II) atom is hexa-coordinated by two chelating diamine ligands and one chelating benzoato ligand. The positive charge of the complex cation is counterbalanced by a benzoate anion, and two additional molecules of benzoic acid are present in the asymmetric unit. Magnetic properties of 1 and 2 were studied in the temperature range 1.8 - 300 K and confirmed strong axial single-ion anisotropy ( D/k B =-7.78 K for 1 , D/kB =-6.52 K for 2 ) of the Ni(II) ions in line with the deformed coordination spheres of the central atoms. In addition, antiferromagnetic spin dimers of Ni(II) ions mediated by hydrogen bonds are present in 1 with exchange coupling J/kB =-2.19 K. The obtained experimental results were supported by ab initio and DFT calculations.