8-(2-Hydroxyphenyl)-1,3-dimethyl-1H-purine-2,6(3H,7H)-dione

The title compound, C13H12N4O3, is an imidazole derivative featuring an annealed purine ring system. The benzimidazole-inspired moiety is essentially planar (r.m.s. of all fitted non-H atoms = 0.0205 Å). An intramolecular O—H⋯N hydrogen bond occurs. In the crystal, intermolecular N—H⋯O and C—H⋯O hydrogen bonds are observed, which connect the molecules into chains along [110]. The shortest centroid–centroid distance between two aromatic systems is 3.7771 (11) Å.

The title compound, C 13 H 12 N 4 O 3 , is an imidazole derivative featuring an annealed purine ring system. The benzimidazoleinspired moiety is essentially planar (r.m.s. of all fitted non-H atoms = 0.0205 Å ). An intramolecular O-HÁ Á ÁN hydrogen bond occurs. In the crystal, intermolecular N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds are observed, which connect the molecules into chains along [110]. The shortest centroidcentroid distance between two aromatic systems is 3.7771 (11) Å .

Related literature
For the crystal structure of benzimidazole, see: Krawczyk & Gdaniec (2005). For the crystal structure of hypoxanthinium nitrate monohydrate as an example of an oxopurine compound, see: Schmalle et al. (1990). For graph-set analysis of hydrogen bonds, see: Etter et al. (1990); Bernstein et al. (1995). For puckering analysis, see: Cremer & Pople (1975). For general information about the chelate effect in coordination chemistry, see: Gade (1998 Table 1 Hydrogen-bond geometry (Å , ). Symmetry codes: (i) Àx þ 1; Ày þ 1; Àz; (ii) Àx þ 2; Ày À 1; Àz.   1998). Combining different sets of donor atoms in one chelate ligand molecule, a probe for testing and accomodating metal centers of different Lewis acidities is at hand. To enable comparative studies with envisioned coordination compounds, we determined the crystal structure of the title compound. The crystal structure of benzimidazole has been reported various times in the literature (e.g. Krawczyk & Gdaniec, 2005). In addition, several oxopurine derivatives have been the topic of crystal structure determinations (e.g. Schmalle et al., 1990).
The molecule features a benzimidazole-inspired backbone comprised of a 6-amino-1,3-dimethylpyrimidine-2,4(1H,3H)dione moiety which is annealed to a five-membered aromatic ring. This part of the molecule is essentially planar (r.m.s. of its fitted non-hydrogen atoms = 0.0205 Å). The small puckering amplitude (τ = 1.6 °) of the six-membered heterocycle precludes a conformation analysis (Cremer & Pople, 1975). The least-squares planes defined by the atoms of the phenyl ring on the one hand and the benzimidazole-type ring system on the other hand enclose an angle of 0.45 (10) ° (Fig. 1).
Both C-N-C angles in the five-membered heterocycle are similar in value with 106.25 (15)° and 104.41 (15)°, with the smaller value found on the non-protonated nitrogen atom. However, these angles are smaller in value than the corresponding ones in hypoxanthinium nitrate monohydrate -invariably above 108 ° -where both nitrogen atoms bear a hydrogen atom (Schmalle et al., 1990).
In the crystal structure, intra-as well as intermolecular hydrogen bonds and C-H···O contacts whose range falls by more than 0.1 Å below the sum of van-der-Waals radii of atoms participating are observed. While the intramolecular hydrogen bonds are exclusively made up by the proton of the hydroxyl group as donor and the non-protonated nitrogen atom of the five-membered heterocycle, intermolecular hydrogen bonds are solely apparent between the amino group and one of the double-bonded oxygen atoms (Table 1). The C-H···O contacts can be separated in two groups: while one of the nitrogenbound methyl groups forms a C-H···O contact involving the oxygen atom of the hydroxyl group, one of the aromatic C-H groups acts as donor for the double-bonded oxygen atom that is already part of the N-H···O type hydrogen bonds. In terms of graph-set analysis (Etter et al., 1990;Bernstein et al., 1995), the descriptor for the classical hydrogen bonds is S(6)R 2 2 (10) on the unitary level. For the C-H···O contacts, a R 2 2 (16)R 2 2 (18) descriptor on the same level is needed for description. In total, the molecules are connected to chains along [1 1 0]. The shortest intercentroid distance between two aromatic systems was measured at 3.7771 (11) Å (Fig. 2).
The packing of the title compound in the crystal is shown in Figure 3. supplementary materials sup-2

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). The nitrogen-bound H atom was located on a difference Fourier map and refined freely. Fig. 1. The molecular structure of the title compound, with atom labels and anisotropic displacement ellipsoids (drawn at 50% probability level).