Creatinium hydrogen oxalate

The crystal structure of the title compound, C4H10N3O2 +·C2HO4 −, is stabilized by N—H⋯O and O—H⋯O hydrogen bonds. The anions are connected by an O—H⋯O hydrogen bond, leading to C(5) chain extending along c axis. The cations are dimerized around the corners of the unit cell, leading to an R 2 2(14) ring motif. This leads to a cationic molecular aggregation at x = 0 or 1 and an anionic molecular aggregation at x = 1/2.

The crystal structure of the title compound, C 4 H 10 N 3 O 2 + Á-C 2 HO 4 À , is stabilized by N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds. The anions are connected by an O-HÁ Á ÁO hydrogen bond, leading to C(5) chain extending along c axis. The cations are dimerized around the corners of the unit cell, leading to an R 2 2 (14) ring motif. This leads to a cationic molecular aggregation at x = 0 or 1 and an anionic molecular aggregation at x = 1/2.
Data collection: SMART (Bruker, 2001); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT; program(s) used to solve structure: SHELXTL/PC (Sheldrick, 2008); program(s) used to refine structure: SHELXTL/PC; molecular graphics: PLATON (Spek, 2009); software used to prepare material for publication: SHELXTL/PC. AJA and SAB sincerely thank the Vice Chancellor and Management of the Kalasalingam University, Anand Nagar, Krishnan Koil, for their support and encouragement. AJA thanks the Principal and Management of the National College of Engineering for their support.
The asymmetric part of the title compound, (I), contains one creatinium cation and one hydrogen oxalate anion (Fig.   1). The protonation of the N site of the cation is evident from C-N bond distances. The deprotonation on the one of the -COOH groups of the oxalic acid is confirmed from that -COObond geometry. The planes of -COOH and -COOgroups are twisted out from each other with an angle of 25.1 (2)°. This twisting of planes may be caused due to the hydrogen bonding association and molecular aggregation. The crystal structure and the molecular aggregations are stabilized through intricate three dimensional hydrogen bonding network ( Fig. 2; Table 1). All the N and O atoms of the cation and anion participate in the hydrogen bonding interactions.
Hydrogen oxalate anions are connected themselves through a O-H···O hydrogen bond leading to a linear chain C(5) motif extending along c axis of the unit cell (Bernstein et al., 1995). Creatinium cations are dimerized around inversion centres of the unit cell, especially at the corners of the unit cell and making a ring R 2 2 (4) motif through N2-H1N···O1 (2 -x, 2 -y, -z) hydrogen bond. Also, these cationic dimers are connected themselves through another N-H···O hydrogen bond leading to a zigzag chain C(7) motif extending along b axis of the unit cell [N3-H3N···O1(-x + 2, y -1/2, -z + 1/2)].

Experimental
The title compound was crystallized from an aqueous mixture containing creatine (0.13g) and oxalic acid (0.09g) in the stoichiometric ratio of 1:1 (20 ml of water) at room temperature by slow evaporation technique.

Refinement
All the H atoms except the atoms involved in hydrogen bonds were positioned geometrically and refined using a riding model, with C-H = 0.96 (-CH 3 ) and 0.97 Å (-CH 2 ) and U iso (H) = 1.2-1.5 U eq (parent atom). H atoms involved in hydrogen bonds were located from differential Fourier maps and refined isotropically. Fig. 1. The molecular structure of the title compound (I) with the numbering scheme for the atoms and 50% probability displacement ellipsoids. H bonds are drawn as dashed lines.

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.