The first dinuclear orotate complex: Syntheses, spectral, thermal and structural characterization of supramolecular orotate complexes of nickel(II) and copper(II) with 2-hydroxyethylpyridine

Two novel orotate complexes, mononuclear [Ni(HOr)(H2O)2(etpy)]·H2O (1) and dinuclear [Cu(μ-HOr)(etpy)]2 (2) (etpy = 2-hydroxyethylpyridine, HOr2− = dianionic orotate), have been prepared and characterized by elemental analyses, spectroscopic (IR, UV-vis), thermal, magnetic and single crystal X-ray diffraction studies. The mononuclear Ni(II) complex crystallizes in the triclinic space group P1¯ and the dinuclear copper(II) complex crystallizes in the monoclinic space group P21/c. The mononuclear complex consists of individual units in which nickel(II) lies on the inversion center and has octahedral coordination by bidentate HOr2−, bidentate etpy and two aqua ligands. The dinuclear copper(II) complex composed of a double-orotate bridge and bidentate etpy ligands. Each HOr2− ligand simultaneously exhibits chelating bidentate and bridging coordination modes. HOr2− is tricoordinated to one copper atom through N3 atom of pyrimidine ring, one oxygen atom of the carboxylate group as a bidentate ligand and to the other copper ion via the other oxygen of the carboxylate group. The structural units are joined into the framework by the hydrogen bonds in 1 and 2.