Creatininium cinnamate

The crystal structure of the title compound (systematic name: 2-amino-1-methyl-4-oxo-4,5-dihydro-1H-imidazol-3-ium 3-phenylprop-2-enoate), C4H8N3O+·C9H7O2 −, is stabilized by N—H⋯O hydrogen bonding. Cations are linked to anions to form ion pairs with an R 2 2(8) ring motif. These ion pairs are connected through a C 2 2(6) chain motif extending along the c axis of the unit cell. This crystal packing is characterized by hydrophobic layers at x ∼ 1/2 packed between hydrophilic layers at x ∼ 0.


Comment
Noncovalent interactions play a vital role in crystal engineering and supramolecular chemistry. Their strength and directionality is responsible for crystal packing and entire molecular arrays (Desiraju, 1989). Our interest lies in the specificity of recognition between inorganic/organic acids and creatinine. Creatinine is 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 (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 of the kidneys. An abnormal level of creatinine in biological fluids is an indicator of various diseases (Narayanan & Appleton, 1980). The asymmetric part of the title compound contains one creatininium cation and one cinnamate anion (Fig. 1). The protonation of the N site of the cation is evident from C-N bond distances. The values are comaparable with creatininium oxalate monohydrate , creatininium benzoate (Bahadur, Sivapragasam et al., 2007) and bis(creatininium) sulfate (Bahadur, Rajalakshmi et al., 2007). The deprotonation on the -COOH group of the cinnamic acid is confirmed from -COObond geometry. The planes of the five-membered creatininium ring and the six-membered cinnamate ring are oriented almost parallel to each other with the dihedral angle of 4.5 (1)°. The plane of the deprotonated carboxylate group is twisted out from the plane of aromatic ring by an angle of 11.5 (3)°.
The crystal structure is stabilized by N-H···O hydrogen bonds ( Fig. 2; Table 1). Cations are linked to anions forming ion pairs through two N-H···O bonds that produce ring R 2 2 (8) motifs around inversion centres (Bernstein et al., 1995).
These ionic dimers are planar and stacked with a dihedral angle of 74.9 (3)°. Further, these adjacent dimers are connected via another N-H···O hydrogen bond leading to chain C 2 2 (6) motif extending along b axis of the unit cell (Fig. 3). Alternate hydrophilic and hydrophobic regions are observed along the a axis of the unit cell. The hydrophobic regions are located at x ~1/2 whereas the hydrophilic regions are located between the hydrophilic layers at x ~0.

Experimental
The title compound was crystallized from an aqueous mixture containing creatinine and cinnamic 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 maps and refined isotropically.  Fig. 1. The molecular structure of the title compound with the numbering scheme for the atoms and 50% probability displacement ellipsoids.