Tetraaquabis(orotato-κO)cobalt(II) dihydrate

In the title CoII complex, [Co(C5H3N2O4)2(H2O)4]·2H2O, the CoII ion is located on an inversion center and is coordinated by two orotate (2,6-dioxo-1,2,3,6-tetrahydropyrimidine-4-carboxylate) anions and four water molecules in a slightly distorted octahedral geometry. The dihedral angle between the carboxylate group and the attached orotate ring is 1.2 (3)°. In the crystal structure, intermolecular O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds link the molecules into a three-dimensional network. π–π contacts between the orotate rings [centroid–centroid distances = 3.439 (2) and 3.438 (2) Å] further stabilize the structure.


Comment
Orotic acid (6-uracilic acid, vitamin B13, H 3 Or) is an essential vitamin in the syntheses of pyrimidine bases of nucleic acids, since it is the first pyridine product of an enzymatic step in normal blood cells (Nelson & Michael, 2000;Smith & Baker, 1959;Levine et al., 1974). Metal orotate complexes and their derivatives not only found applications in curing syndromes but also they have encouraging studies as therapeutic agents for cancer (Schmidbaur et al., 1990;Castan et al., 1990;Köse et al., 2006). Orotic acid is an interesting ligand because it has multiple coordination sites at low and neutral pH, it is coordinated from the carboxylic acid group monodentately in ketonic form but at higher pH values bidentate coordination occurs in enolic form, the tautomerism between the ketonic and enolic structures makes multiform coordinations possible (Doody et al., 1996;Köse et al., 2008). Mononuclear crystal structures of Co, Cu, Mg, Ni and Zn complexes were reported, where bidentate orotate dianions (HOr 2-) found in the molecules (Mutikainen, 1987;Mutikainen et al., 1996;Icbudak et al., 2003;Sabat et al., 1980;Karipides & Thomas, 1986;Platter et al., 2002;Kumberger et al., 1991). Dianionic form of the acid (HOr 2-) can also act as a polydentate ligand in its polymeric complexes with Cu, Ni and Mn metals (Nepveu et al., 1995;Ha et al., 1999;Platter et al., 2002;Sun et al., 2002). Relatively limited number of monoanionic orotate complex crystal studies are found in the literature. The metal orotate structures including Mg, Ni and Zn have (H 2 Or -) ions located in the outer coordination sphere and the monoanion does not enter the inner coordination sphere of the aquated metal, M(II), cations (Solbakk, 1971). The title compound was synthesized and its crystal structure is reported herein.  (Table 2) link the molecules into a three-dimensional network, in which they may be effective in the stabilization of the structure. The π-π contacts between the Or rings, Cg1-Cg1 i and Cg1-Cg1 ii [symmetry codes: (i) x, 1/2 -y, z -1/2; (ii) x, 1/2 -y, z + 1/2, where Cg1 is the centroid of the ring (N1/N2/C2-C5)] may further stabilize the structure, with centroid-centroid distances of 3.439 (2) and 3.438 (2) Å, respectively.

supplementary materials sup-2 Experimental
The title compound was prepared by the reaction of NH 4 H 2 Or (0.96 g, 5 mmol) in H 2 O (100 ml) and nicotinamide (1.22 g, 10 mmol) in H 2 O (100 ml) with Co(NO 3 ) 2 .6H 2 O (1.45 g, 5 mmol) in H 2 O (50 ml). The mixture was filtered and set aside to crystallize at ambient temperature for one week, giving pink single crystals.

Refinement
The highest peak and deepest hole in the final difference electron-density map were located 1.99 and 0.49 Å, respectively, from atom Co1. Atom H5 was positioned geometrically with C-H = 0.93 Å, for aromatic H atom and constrained to ride on its parent atom, with U iso (H) = 1.2U eq (C). Atoms H1, H2 (for NH), H51, H52, H61, H62, H71, H72 (for H 2 O) were located in difference Fourier maps and refined isotropically, with restrains of N1-H1 = 0.83 (2) Fig. 1. The molecular structure of the title molecule with the atom-numbering scheme. Displacement ellipsoids are drawn at the 40% probability level. Primed atoms are generated by the symmetry operator:(') -x, -y, -z.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )