Crystal structure of 6-hydroxy-5-(2-methoxyphenoxy)-2,2′-bipyrimidin-4(3H)-one

In the crystal, a combination of N—H⋯O and O—H⋯O hydrogen bonds links the molecules of the title compounds into a chain of rings.


Structural commentary
The bond distances in the ring containing atom N11 clearly show the presence of localized double bonds in the bonds C12 N13 and C14 C15 as well as the exocyclic C16 O16, fully consistent with the location of the H atoms on atoms N11 and O14, as deduced from difference maps and confirmed by the refinement. By contrast, the bond distances in the other heterocyclic ring indicate conventional aromatic-type delocalization.
At each of the sites C14, C31 and C32, the corresponding pairs of exocyclic O-C-N (at C14) or O-C-C angles (at C31 and C32) differ by almost 10 , as generally observed in the arenes of type ArOR when the substituent R lies close to the plane of the aryl ring (Seip & Seip, 1973;Ferguson et al., 1996). Here atoms C15 and C37 (Fig. 1) are displaced from the plane of the aryl ring (C31-C36) by 0.219 (3) and 0.204 (4) Å , respectively, with both substituents displaced to the same side of the aryl ring. The C-O-C angles at atoms O15 and O32, 115.41 (12) and 117.65 (18) respectively, and the C-O-H angle at atom O14 is 114.2 (16) ; are all significantly larger the the idealized tetrahedral value of 109.5 .

Figure 2
Part of the crystal structure of compound (I) showing the formation of a hydrogen-bonded C(5) C(6)[R 2 2 )9)] chain of rings parallel to [001]. For the sake of clarity, the H atoms bonded to C atoms have all been omitted. no internal symmetry and thus the compound is conformationally chiral: the centrosymmetric space group confirms that (I) crystallizes as a conformational racemate.

Supramolecular interactions
In the crystal, molecules of (I) are linked by a combination of O-HÁ Á ÁN and N-HÁ Á ÁN hydrogen bonds (Table 1) to form a C(5) C(6)[R 2 2 (9)] chain of rings running parallel to the [001] direction ( Fig. 2): adjacent molecules are related by glideplane symmetry. Two chains of this type, related to one another by inversion, pass through each unit cell, but there are no direction-specific interactions between adjacent chains.

Database survey
In the dihydrate (II), an extensive series of hydrogen bonds, encompassing N-HÁ Á ÁO, O-HÁ Á ÁN and O-HÁ Á ÁO types links the molecular components into a complex sheet structure (Yamuna et al., 2013), in contrast to the rather simple chains in (I) reported here. A sheet structure, built from a combination of the same three types of hydrogen bond is found also in the structure of bosentan monohydrate .

Synthesis and crystallization
A sample of compound (I) was a gift from Cadila Pharmaceuticals Ltd, Ahmedabad, Gujarat, India. Colourless plates of the anhydrous compound (I) were grown by slow evaporation, at room temperature of a solution of (I) in a mixture of dimethylsulfoxide and N,N-dimethylformamide (1:1, v/v) containing an excess of adipic acid (hexane-1,6-dioic acid).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. All H atoms were located in difference maps. The H atoms bonded to C atoms were then treated as riding atoms in geometrically idealized positions with C-H distances 0.93 Å (aromatic and heteroaromatic) or 0.96 Å (CH 3 ) and with U iso (H) = kU eq (C) where k = 1.5 for the methyl group, which was permitted to rotate but not to tilt and 1.2 for all other H atoms bonded to C atoms. For the H atoms bonded to O or N atoms, the atomic coordinates were refined with U iso (H) = 1.5U eq (O) or 1.2U eq (N), giving the O-H and N-H distances shown in Table 1.

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