Creatininium hydrogen maleate

In the title compound, C4H8N3O+·C4H3O4 −, the cations and anions are linked through N—H⋯O hydrogen bonds making a ionic pair with an R 2 2(8) ring motif. These ionic pairs are further connected through another N—H⋯O hydrogen bond, leading to an R 6 6(16) ring motif around the inversion centres of the unit cell. These approximately planar aggregates are further connected through weak van der Waals interactions in the unit cell. The anions have a characteristic intramolecular O—H⋯O hydrogen bond with a self-associated ring S(7) motif.

In the title compound, C 4 H 8 N 3 O + ÁC 4 H 3 O 4 À , the cations and anions are linked through N-HÁ Á ÁO hydrogen bonds making a ionic pair with an R 2 2 (8) ring motif. These ionic pairs are further connected through another N-HÁ Á ÁO hydrogen bond, leading to an R 6 6 (16) ring motif around the inversion centres of the unit cell. These approximately planar aggregates are further connected through weak van der Waals interactions in the unit cell. The anions have a characteristic intramolecular O-HÁ Á ÁO hydrogen bond with a self-associated ring S(7) motif.

Comment
Intermolecular forces play an essential role in the formation of supramolecular systems which are useful for definite social applications. In which, the phenomenon of hydrogen bond has its importance in the areas of molecular recognition, crystal engineering research and supramolecular chemistry. Their strength and directionality is responsible for crystal packing and entire molecular arrays (Desiraju, 1989). We are interested on the the specificity of recognition between inorganic / organic acids and cretinine molecule. Creatinine, a blood metabolite of considerable importance in clinical chemistry, particularly as an indicator of renal function. It has been proven that determination of creatinine is more valuable for the detection of renal dysfunction than that of urea (Sharma et al., 2004). In renal physiology, creatinine clearance (CCr; Madaras & Buck, 1996) is the volume of blood plasma that is cleared of creatinine per unit time. Clinically, creatinine clearance is a useful measure for estimating the glomerular Filtration rate (GFR) of the kidneys. Anabnormal level of creatinine in biological fluids is an indicator of various disease states (Narayanan & Appleton, 1980). The asymmetric part of the title compound, (I), contains one creatininium cation and one maleate anion (Fig.1). The protonation of the N site of the cation is evident from C-N bond distances and the other bond distances and angles are comaparable with Creatininium cinnamate (Ali et al., 2011), Creatininium hydrogen oxalate monohydrate , Creatininium benzoate (Bahadur, Sivapragasam et al., 2007) and bis(creatininium) sulfate (Bahadur, Rajalakshmi et al., 2007). The deprotonation on the one of the -COOH groups of the maleic acid is confirmed from that -COObond geometry.
In the crystal structure, the molecular aggregations are stabilized through a two dimensional hydrogen bonding pattern ( Fig. 2; Table 1). Cations are linked to anions forming an ion pair through two N-H···O bonds that produce ring R 2 2 (8) motifs (Bernstein et al., 1995). The same type of ring motif is observed in previously reported structures from our laboratory. Anions are having a characteristic intramolecular O-H···O hydrogen bond with a self-associated S(7) motif. This cation-anion pairs are further linked through another N-H···O hydrogen bond leading to a ring R 6 6 (16) motif around the inversion centres of the unit cell. This ring motifs are almost planar. These ring motifs are connected through weak Van der Waals interactions in the unit cell.

Experimental
The title compound was crystallized from an aqueous mixture containing creatinine and maleic acid in the stoichiometric ratio of 1:1 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 = 0.93 (-CH) and 0.96 Å (-CH 3 ) and U iso (H) = 1.2-1.5 U eq (parent atom). H atoms involved in hydrogen bonds were located from differential fourier map 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.  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.