Bis(creatininium) tetrachloridocadmate(II)

In the title compound, (C4H8N3O)2[CdCl4], the asymmetric unit comprises two creatininium cations and one tetrachloridocadmate anion. Cd⋯O secondary bonding links one of the two imidazole rings and the anion into ion pairs. The free and bound cations form layers between which the [CdCl4]2− anions are sandwiched. The CdII atom adopts a distorted trigonal-bipyramidal geometry in which the Cd⋯O bond is axial. Intermolecular N—H⋯Cl hydrogen bonds form a two-dimensional network parallel to (001) which ensures the junction between creatininium cations and [CdCl4]2− anions.

In the title compound, (C 4 H 8 N 3 O) 2 [CdCl 4 ], the asymmetric unit comprises two creatininium cations and one tetrachloridocadmate anion. CdÁ Á ÁO secondary bonding links one of the two imidazole rings and the anion into ion pairs. The free and bound cations form layers between which the [CdCl 4 ] 2À anions are sandwiched. The Cd II atom adopts a distorted trigonal-bipyramidal geometry in which the CdÁ Á ÁO bond is axial. Intermolecular N-HÁ Á ÁCl hydrogen bonds form a two-dimensional network parallel to (001) which ensures the junction between creatininium cations and [CdCl 4 ] 2À anions.

Experimental
Crystal data (C 4   Creatinine (2-amino-1,5-dihydro-1-methyl-4H-imidazol-4-one) is the waste product of protein metabolism that is found in the urine. It can be measured to assess overall kidney function. An abnormal level of creatinine in biological fluids is an indicator of various malady states (Narayanan & Appleton, 1980). Over the last decade, there have been an increasing number of reports on compounds resulting from the combination of creatinine and biologically important metal ions, in order to obtain structural information on the mode of interaction between them. (Canty et al., 1979), however, the different complex species are formed depending on the reaction conditions (Nishida & Kida, 1985). In the title compound, (I), we determine the crystal structure of a new cadmium complex showing the metal coordination and the structure cohesion. It is the first example of salt containing creatininium cation and (CdCl 4 ) 2anion.
The asymmetric unit, shown in Fig. 1, consists of the tetrachlorocadmate anion and two cations of creatinine protonated.
As expected, creatininium cations are approximately planar. In the bound cation, the r.m.s. deviation for the non-H atoms = 0.0311 Å, the maximum deviation of N5 from the mean plane is 0.0592 (15) Å. However, the free cation has a r.m.s deviation for non-H atoms = 0.0488 Å with a maximum deviation from the mean plane = 0.0851 (0.11) Å (for O2).
In table 1, we notice that in each creatininium cation, the three C-N bond distances are clearly different, with C6-N4 and C3-N1 much longer than the other ones. This results in the localization of the exocyclic C3-N2 [1.325 (2) (Smith & White, 2001). Such difference in C-N bonds has been reported in some creatinium compounds (Wilkinson et al., 2005).

Experimental
The title compound was crystallized from a supersaturated hydrochloric acid solution (45%, 5 ml) prepared using doubly distilled water and a mixture of cadmium(II) chloride (1.83 g) and creatinine (2.26 g). Colourless plates-shaped single crystals of (I) were obtained at ambient temperature by slow evaporation of the solution.

Refinement
The iminium and ammino H atoms were located in a difference Fourier map and was refined isotropically. The methyl H atoms were constrained to an ideal geometry (C-H = 0.96 Å) with U iso (H) = 1.2U eq (C), but were allowed to rotate freely about the C-C bonds. The methylene H atoms were placed in geometrically idealized positions (C-H = 0.97 Å) and constrained to ride on their parent atoms with U iso (H) = 1.2U eq (C). Fig. 1. The independent components of (I), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level. Fig. 2. Part of the crystal structure of (I), showing the formation of the R 2 2 (8), R 2 4 (12) and R 6 6 (28) rings. Hydrogen bonds are shown as dashed lines. Hydrogen atoms not involved in the motif have been omitted for clarity. Crystal data (C 4  0.0226 (9) 0.0115 (9) 0.0158 (9) −0.0026 (7) 0.0017 (7) −0.0031 (7) Geometric parameters (Å, °)