Pyridinium trans-diaquabis[oxalato(2−)-κ2 O 1,O 2]chromate(III) urea monosolvate

The asymmetric unit of the title solvated molecular salt, (C5H6N)[Cr(C2O4)2(H2O)2]·CO(NH2)2, contains half a formula unit. Each component is completed by crystallographic twofold symmetry: in the cation, one C and the N atom lie on the rotation axis; in the anion, the CrIII ion lies on the axis; in the solvent molecule, the C and the O atom lie on the axis. The aqua ligands are in a trans disposition in the resulting CrO6 octahedron. In the crystal, the components are linked by O—H⋯O, N—H⋯O and N—H⋯(O,O) hydrogen bonds, generating a three-dimensional network.

The asymmetric unit of the title solvated molecular salt, (C 5 H 6 N)[Cr(C 2 O 4 ) 2 (H 2 O) 2 ]ÁCO(NH 2 ) 2 , contains half a formula unit. Each component is completed by crystallographic twofold symmetry: in the cation, one C and the N atom lie on the rotation axis; in the anion, the Cr III ion lies on the axis; in the solvent molecule, the C and the O atom lie on the axis. The aqua ligands are in a trans disposition in the resulting CrO 6 octahedron. In the crystal, the components are linked by O-HÁ Á ÁO, N-HÁ Á ÁO and N-HÁ Á Á(O,O) hydrogen bonds, generating a three-dimensional network.

Experimental
1 mmol (267 mg) of CrCl 3 ·6H 2 O was dissolved in 50 ml of water. The green filtered solution was stirred at 323 K, 2 mmol (253 mg) of oxalic acid, 1 mmol (79.1 mg) of pyridine and 2 mmol (121 mg) of urea were added in successive small portions and stirred for 2 h. The resulting violet solution was left at room temperature; violet prisms were obtained after one week of slow evaporation.

Refinement
The H atoms of the pyridimium cation were positioned geometrically, with C-H, N-H distances of 0.93 and 0.86 Å respectively, and constrained to ride on their parent atoms, with U iso (H) = 1.2U eq (C, N). The urea H atoms were located in a difference Fourier map and freely refined. program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2010); software used to prepare material for publication: WinGX (Farrugia, 2012).

Figure 1
Molecular structure of the title compound with displacement ellipsoids drawn at the 50% probability level.

sup-3
Acta Cryst. (2013). E69, m567  Interconnection of the constituents of the title compound into a three-dimensional network. Hydrogen bonds are highlighted with dashed lines.

Pyridinium trans-diaquabis[oxalato(2-)-κ 2 O 1 ,O 2 ]chromate(III) urea monosolvate
Crystal data (C 5  Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(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.