Solid-state chemistry of nickel(II)-oxalate-amine systems. Synthesis, characterization and crystal structure of the bis(2,2′-bipyridine) (oxalato-O,O′)nickel(II) tetrahydrate

Abstract

Purple single crystals of the mononuclear mixed-ligand complex [Ni(ox)(bipy) 2]·4H 2O, where ox is oxalate and bipy is 2,2′-bipyridine, were obtained by slow evaporation of a solution previously prepared by adding an ethanolic bipy solution to an aqueous solution of nickel(II) chloride hexahydrate and potassium oxalate monohydrate (molar ratio 1:2). The compound was characterized by elemental analysis, FT-IR spectroscopy and single-crystal X-ray diffraction. The crystal structure consists of neutral mono-nuclear [Ni(ox)(bipy) 2] units and crystallization water molecules which are held together by an extensive three-dimensional network of OH…O and CH…O hydrogen bonds and face-to-face stacking interactions between the π-systems of the bipy aromatic rings. The nickel atom is coordinated by two oxygen atoms of a bidentate oxalate ligand and four nitrogen atoms belonging to two bipy in an octahedral cis arrangement. Thermal decomposition of the complex was studied by TG-DTA techniques in synthetic air and argon atmospheres.