The first dinuclear orotate complex: Syntheses, spectral, thermal and structural characterization of supramolecular orotate complexes of nickel(II) and copper(II) with 2-hydroxyethylpyridine Okan Zafer Yes ßilel a, * , Aylin Mutlu a , Cemil Ög ˘retir a , Orhan Büyükgüngör b a Department of Chemistry, Faculty of Arts and Sciences, Eskis ßehir Osmangazi University, 26480 Eskis ßehir, Turkey b Department of Physics, Faculty of Arts and Sciences, Ondokuz Mayıs University, 55139 Kurupelit, Samsun, Turkey article info Article history: Received 24 October 2007 Received in revised form 21 February 2008 Accepted 21 February 2008 Available online 29 February 2008 Keywords: Orotate complexes 2-Hydroxyethylpyridine Dinuclear orotate complex Dinuclear copper(II) complex abstract Two novel orotate complexes, mononuclear [Ni(HOr)(H 2 O) 2 (etpy)]H 2 O(1) and dinuclear [Cu(l-HOr) (etpy)] 2 (2) (etpy = 2-hydroxyethylpyridine, HOr 2 = dianionic orotate), have been prepared and charac- terized 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 P  1 and the dinuclear copper(II) complex crystallizes in the monoclinic space group P2 1 /c. The mononuclear complex consists of individual units in which nickel(II) lies on the inversion center and has octahedral coordina- tion by bidentate HOr 2 , bidentate etpy and two aqua ligands. The dinuclear copper(II) complex com- posed of a double-orotate bridge and bidentate etpy ligands. Each HOr 2 ligand simultaneously exhibits chelating bidentate and bridging coordination modes. HOr 2 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. Ó 2008 Elsevier B.V. All rights reserved. 1. Introduction Orotic acid has a great importance in the field of biological activity, that is meaning vitamin B13 (Scheme 1) [1–5]. Mono- and dianion of orotic acid are potential polydentate ligands. The coordination may occur through the heterocyclic nitrogens of the pyrimidine ring, the exocyclic carbonyl oxygens, and the carboxylic group. The orotato anion may exhibit versatile coordi- nating modes such as monodentate [6–12], bidentate [13–33], bridging ligand [34–39] and counter anion [40–43]. To our knowl- edge, so far the only one structural characterization of polymeric copper–orotate complex has been reported [34] and X-ray crystal structures of a few mononuclear copper(II) orotate complexes have appeared in the literature [8,15,23,28,32,44,45]. Although orotic acid has been studied extensively, both structurally and spectro- scopically for many years [10–12], the dinuclear complexes of this ligand have not been reported. In the polymeric orotate complex, [Cu(HOr)(H 2 O) 2 ] n [34] the carboxylate group acts as a bridge be- tween two metal atoms using its two oxygen atoms of carboxylate group. By contrast, in polymeric Co(III) and Ni(II) complexes [30], metal ions are coordinated to one orotato ligand at the N3 ring nitrogen and the adjacent carboxylate oxygen and to another oro- tato anion at the exocyclic carbonyl oxygen. In the [Cu(HOr)(NH 3 ) 2 ] [15] and [Cu(HOr)(phen)] [23] complexes, orotate is coordinated to the copper ion through nitrogen atom of pyrimidine ring and oxy- gen atom of carboxylate group as a chelate manner. The primary coordination spheres about copper(II) were square–planer and they were extended to octahedral coordination by exocyclic keto- oxygens or other oxygen atom of carboxylate group of the symme- try related complex units. Following of our work on [24–28,39,42–45], we now are report- ing on the preparation, spectral, thermal and structural character- ization of orotate complexes of nickel(II) and copper(II) with 2-hydroxyethylpyridine (Scheme 1b). 2. Experimental 2.1. Preparation of the complexes A solution of etpy (0.44 g, 4 mmol) in ethanol (5 mL) was added dropwise upon stirring to a solution of [Ni(HOr)(H 2 O) 4 ]H 2 O [20] (0.61 g, 2 mmol) and [Cu(HOr)(H 2 O) 4 ]H 2 O [24] (0.62 g, 2 mmol) in distilled water (30 mL). The solution was heated to 60 °C in a temperature-controlled bath and stirred for 5 h at 60 °C. Then the reaction mixture was cooled to room temperature. The formed 0022-2860/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2008.02.029 * Corresponding author. Tel.: +90 222 2393750; fax: +90 222 2393578. E-mail address: yesilel@ogu.edu.tr (O.Z. Yes ßilel). Journal of Molecular Structure 889 (2008) 415–421 Contents lists available at ScienceDirect Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc