Diaquabis(5-carboxy-2-ethyl-1H-imidazole-4-carboxylato-κ2 N 3,O 4)cobalt(II) trihydrate

In the title compound, [Co(C7H7N2O4)2(H2O)2]·3H2O, the CoII cation, located on an inversion center, is N,O-chelated by two 5-carboxy-2-ethyl-1H-imidazole-4-carboxylate anions and further coordinated by two water molecules in a distorted octahedral geometry. Only one carboxy group of the anion is deprotonated, and the two carboxyl groups of the same anion are linked via an intramolecular O—H⋯O hydrogen bond. One of the lattice water molecules is located on an inversion center, its H atom equally disordered over two positions. One of H atoms of another lattice water molecules is also equally disordered over two sites. Water H atoms and the amino H atom all are involved in an intermolecular hydrogen-bonded network in the crystal.

Data collection: APEX2 (Bruker, 2007); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL. Crystal engineering of mental-organic complexes is a very active research field. It is well known that organic ligands play a crucial role in the design and construction of desirable frameworks. In recent years, multifunctional ligands containing N-and O-donors have attracted great attention due to the fact that they may induce diversity in the coordination modes and interesting properties. In our previous work, we have done a lot of research on the design and synthesis of new compounds built from the imidazole derivatives (Fan et al., 2010;Li et al., 2011;He et al., 2010;Song et al., 2010;Yan et al., 2010). To continue our study, we report here the structure of the title Co(II) complex.
As illustrated in Fig. 1, The Co II ion adopts a slightly distorted octahedral geometry, with two N,O-bidentate ligands ([Co-O = 2.155 (3) Å and Co-N = 2.128 (2) Å) from the imidazoledicarboxylic group at the equatorial positions, the other two oxygen atoms (Co-O = 2.060 (2) Å) from two water molecules occupied the axial position. In the crystal structure, the complex molecules and solvent molecules are linked by O-H···O and N-H···O hydrogen bonds, forming the final three-dimensional supra-molecular network. A lattice water molecule is located on an inversion center, and one H atom of another water molecule was split into two positions with half occupancy.
Red crystals were obtained by slow evaporation of the solvent at room temperature with the yeild of 32% based on Co.

Refinement
H atoms of the water molecule were located in a difference Fourier map and refined as riding with an O-H distance restraint of 0.82 (1) Å, with U iso (H) = 1.5U eq (O). The H···H distances within the water molecules were restraint to 1.30 (1) Å. Carboxyl H atoms were located in a difference map but were refined as riding on the parent O atoms with O-H = 0.82 Å and U iso (H) = 1.5 U eq (O). Carbon and nitrogen bound H atoms were placed at calculated positions and were treated as riding on the parent C or N atoms with C-H = 0.96 (methyl), 0.97 (methylene) and N-H = 0.86 Å, U iso (H) = 1.2 or 1.5U eq (C,N). The O3w is located on an inversion center, its H atoms were equally disordered over two positions.
One of H atoms of O2w water molecules is also equally disordered over two sites.

Figure 1
The structure of the title compound, showing the atomic numbering scheme. Non-H atoms are shown with 30% probability displacement ellipsoids. (symmetry codes: i = 1-x, -y, 1-z).

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 R-factors(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 )
x y z U iso */U eq Occ. (