Creatininium 2-chloroacetate

In the title compound (systematic name: 2-amino-1-methyl-4-oxo-4,5-dihydro-1H-imidazol-3-ium 2-chloroacetate), C4H8N3O+·C2H2ClO2 −, the molecular aggregations are stabilized through classical (N—H⋯O) and non-classical (C—H⋯O and C—H⋯N) hydrogen-bonding interactions. The cations are linked to the anions, forming ion pairs through two N—H⋯O bonds that produce characteristic R 2 2(8) ring motifs. These cation–anion pairs are connected through another N—H⋯O hydrogen bond, leading to an R 4 2(8) ring motif. Further weak C—H⋯N interactions link the molecules along the a axis, while other C—H⋯O interactions generate zigzag chains extending along b.

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) Creatinine, a nitrogenous organic acid, is found in the muscle tissue of vertebrates mainly in the form of phosphocreatine and supplies energy for muscle contraction. Also, it 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 rate, 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. An abnormal level of creatinine in biological fluids is an indicator of various disease states (Narayanan & Appleton, 1980). Also, the effective protonation site on the creatinine molecule (N atoms) can form intermolecular interactions such as hydrogen bonds that play an essential role in the formation of supramolecular systems. As we have stated in our previous papers, we are interested on the the specificity of recognition between inorganic / organic acids and the cretinine molecule. Hence, the title compound is reported here.
The asymmetric unit of the title compound, (I), contains one protonated creatinine molecule as the creatininium cation and one deprotonated monochloroacetic acid as the monochloroacetate anion (Fig.1). Protonation of the N site of the cation is evident from C-N bond distances and the C-N-C bond angle. Other bond distances and angles are comparable with those found in creatininium hydrogen maleate (Ali et al., 2011a), creatininium cinnamate (Ali et al., 2011b), creatininium hydrogen oxalate monohydrate , creatininium benzoate (Bahadur, Sivapragasam et al., 2007) and bis(creatininium) sulfate (Bahadur, Rajalakshmi et al., 2007). The deprotonation on the -COOH groups of the monochloroacetic acid is confirmed from the -COObond geometry. The plane of the five membered ring in the cation and that of the carboxylate group of the anion are oriented at an angle of 9.5 (1)°.
In the crystal structure, molecular aggregations are stabilized through classical (N-H···O) and non-classical (C-H···O and C-H···N) hydrogen bonding interactions (Table 1). Cations are linked to anions forming ion pairs through two N-H···O bonds that produce characterestic R 2 2 (8) ring motifs (Bernstein et al., 1995). This type of ring motif is observed in most structures of creatinine salts of inorganic/organic acids, especially when carboxylate anions are present (Fig. 2).

Experimental
The title compound was crystallized from an aqueous mixture containing creatinine and monochloroacetic acid in a 1:1 stoichiometric ratio at room temperature by the slow evaporation technique.

Refinement
H atoms bound to N and involved in hydrogen bonds were located from a difference Fourier map and refined isotropically. Other H atoms except 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).

Figure 1
The asymmetric unit of the title compound (I) with the numbering scheme for the atoms and 50% probability

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'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 > σ(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.