2-[(E)-(6-Amino-1,3-dimethyl-2,4-dioxo-1,2,3,4-tetrahydropyrimidin-5-yl)iminomethyl]pyridinium chloride monohydrate

The title compound, C12H14N5O2 +·Cl−·H2O, is the monohydrate of the hydrochloride of an oxopurine-derived Schiff base in which protonation took place at the pyridine N atom. The organic cation is essentially planar (r.m.s. of all fitted non-H atoms = 0.0373 Å). In the crystal, N—H⋯O and N—H⋯Cl hydrogen bonds as well as C—H⋯O and C—H⋯Cl contacts connect the different entities into a three-dimensional network. The shortest centroid–centroid distance between two pyrimidine rings is 3.6364 (9) Å.

The title compound, C 12 H 14 N 5 O 2 + ÁCl À ÁH 2 O, is the monohydrate of the hydrochloride of an oxopurine-derived Schiff base in which protonation took place at the pyridine N atom. The organic cation is essentially planar (r.m.s. of all fitted non-H atoms = 0.0373 Å ). In the crystal, N-HÁ Á ÁO and N-HÁ Á ÁCl hydrogen bonds as well as C-HÁ Á ÁO and C-HÁ Á ÁCl contacts connect the different entities into a three-dimensional network. The shortest centroid-centroid distance between two pyrimidine rings is 3.6364 (9) Å .
Data collection: APEX2 (Bruker, 2010); cell refinement: SAINT (Bruker, 2010); data reduction: SAINT; program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997) and Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXL97 and PLATON (Spek, 2009 2-[(E)-(6-Amino-1,3-dimethyl-2,4-dioxo-1,2,3,4-tetrahydropyrimidin-5yl)iminomethyl]pyridinium chloride monohydrate I. Booysen, M. Ismail, T. Gerber, E. Hosten and R. Betz Comment Next to cardiovascular diseases, cancer has become one of the main fatal diseases in industrialized countries. Apart from classical surgery, chemo-and radiotherapeutic treatments have entered the arsenal of possible cures for certain types of cancer. All methods, however, suffer from their own set of problematic side-effects and, as a consequence, the development of radiopharmaceuticals -combining the advantages of chemotherapy as well as radiation methods while at the same time avoiding their unique respective undesired side-effects -has been a topic of research (Gerber et al., 2011). Tailoring and fine-tuning of the envisioned radiopharmaceuticals' properties such as lipophilicity and, in particular, inertness is of paramount importance with respect to possible future in vivo applications in contemporary medicine and requires sound knowledge about structural parameters of the ligands applied if a more heuristic approach in the synthesis is to triumph over pure trial-and-error as it is encountered in this specific field of coordination chemistry up to the present day. To allow for an assessment of changes in structural features upon coordination has taken place, the molecular and crystal structure The organic cation is essentially planar (r.m.s. for all its fitted non-hydrogen atoms = 0.0373 Å). The low puckering amplitude (τ = 2.2 °, r.m.s. for all its fitted and bonded non-hydrogen atoms = 0.0373 Å) of the non-aromatic heterocycle precludes a conformational analysis (Cremer & Pople, 1975) (Fig. 1).
In the crystal, hydrogen bonds as well as C-H···O and C-H···Cl contacs are observed whose range fall by about and more than 0.1 Å below the sum of van-der-Waals radii of the atoms participating for the latter two types of interaction.
The classical hydrogen bonds are supported by the protons of the water molecule as well as the amino group and have the chloride ion, the oxygen atom of the water molecule and the oxygen atom of the keto group located between the two methylated nitrogen atoms as acceptor. Two C-H···O contacts can be observed: the first one stemming from the C-H group in ortho-position to the protonated nitrogen atom in the pyridyl moiety and the keto group not acting as acceptor for a classical hydrogen bond and the second one between the C-H group in para position to the protonated nitrogen atom of the pyridyl moiety and the keto group that is already acting as acceptor for one of the classical hydrogen bonds. The two C-H···Cl contacts apply the vinylic hydrogen atom as well as one of the C-H groups present in the pyridyl moiety as donors.
The chloride anion thus is pentacoordinate. A description of the classical hydrogen bonds in terms of graph-set analysis (Etter et al., 1990;Bernstein et al., 1995) necessitates a DDDDD descriptor on the unitary level while the C-H···O as well as the C-H···Cl contacts can be described by means of a DDC 1 1 (9)C 1 1 (11) descriptor on the same level. In total, the entities of supplementary materials sup-2 the title compound are connected to a three-dimensional network. The shortest intercentroid distance between two centers of gravity was found at 3.6364 (9) Å (Fig. 2).
The packing of the title compound in the crystal structure is shown in Figure 3.

Refinement
Carbon-bound H atoms were placed in calculated positions (C-H 0.95 Å) and were included in the refinement in the riding model approximation, with U(H) set to 1.2U eq (C). The H atoms of the methyl groups were allowed to rotate with a fixed angle around the C-C bond to best fit the experimental electron density (HFIX 137 in the SHELX program suite (Sheldrick, 2008)), with U(H) set to 1.5U eq (C). All nitrogen-bound H atoms as well as the hydrogen atoms of the molecule of crystal water were located on a difference Fourier map and refine freely.