Comment

The crystal structures of various aminopyrimidine carboxylates (Hu et al., 2002) and cocrystals (Chinnakali et al., 1999) have been described. From our laboratory, the crystal structures of 2-amino-4,6-dimethylpyrimidinium bromide 2-amino-4,6-dimethylpyrimidine monohydrate (Panneerselvam et al., 2004) and 2-amino-4,6-dimethylpyrimidine cinnamic acid (1/2) (Balasubramani et al., 2005) have been reported. In this paper, the hydrogen-bonding patterns in the title compound, (I), are described.

The asymmetric unit of (I) contains a 2-amino-4,6-dimethylpyrimidine (AMPY) molecule and a 4-hydroxybenzoic (4-HBZ) acid molecule (Fig. 1). Both species are neutral, thus (I) is an adduct rather than a molecular salt. Atoms O2 and the -N2H₂ group act as hydrogen-bond donors to atoms N1 and O3, respectively, to form an eight-membered ring, which has the graph-set notation R₂²(8) (Etter, 1990; Bernstein et al., 1995). This type of interaction has been observed in the crystal structures of other 2-aminopyrimidine-carboxylic acid adducts (Lynch & Jones, 2004).

The second H atom of the 2-amino group links to an O2 atom in an adjacent molecule via an N-HO bond, and one of the C atoms (C11) of 4-HBZ is hydrogen bonded to O3 via a C-HO interaction to form a ring having graph-set notation R₂³(8), leading to the supramolecular chain shown in Fig. 2. Hence, O3 acts as a bifurcated acceptor. The 4-HBZ hydroxy (O1) group is hydrogen bonded to pyrimidine atom N3 via an O-HN interaction, to form a chain as shown in Fig. 3.

Aromatic - interactions between the pyrimidine ring of AMPY and the benzene ring of 4-HBZ are also observed in (I). The perpendicular separation is 3.552 Å, and the centroid-to-centroid distance is 3.660 (9) Å. The slip angle (the angle between the centroid-to-centroid vector and the normal to the plane) is 19.86°. These values are typical for aromatic - stacking interactions (Hunter, 1994).

Figure 1 ORTEPII (Johnson, 1976) view of the asymmetric unit of (I), showing 50% probability displacement ellipsoids. Dashed lines indicate hydrogen bonds.

Figure 2 A view of the supramolecular chain in (I). Dashed lines indicate hydrogen bonds and H atoms not involved in hydrogen bonding have been omitted. [Symmetry codes: (ii) x, -y,  + z; (iii) x, -y, z - .]

Figure 3 A view of the hydrogen-bonding patterns in (I). Dashed lines indicate hydrogen bonds and H atoms not involved in hydrogen bonding have been omitted. [Symmetry code: (i) 1 + x, -y, z - .]

Experimental

Hot methanol solutions (20 ml) of 2-amino-4,6-dimethylpyrimidine (30 mg, Aldrich) and 4-hydroxybenzoic acid (32 mg, LOBA Chemie, India) were mixed and warmed over a water bath for a few minutes. The resulting solution was allowed to cool slowly at room temperature. Crystals of (I) appeared from the mother liquor after a few days.

Crystal data

C6H9N3·C7H6O3 Mr = 261.28 Monoclinic, C c a = 9.0693 (3) Å b = 11.1141 (4) Å c = 12.6080 (5) Å = 102.916 (2)° V = 1238.70 (8) Å3 Z = 4 Dx = 1.401 Mg m-3 Mo K radiation = 0.10 mm-1 T = 120 (2) K Cube, colourless 0.20 × 0.20 × 0.20 mm

Data collection

Bruker-Nonius KappaCCD diffractometer and scans Absorption correction: multi-scan (SORTAV; Blessing, 1995) Tmin = 0.980, Tmax = 0.980 4983 measured reflections 1419 independent reflections 1360 reflections with I > 2(I) Rint = 0.023 max = 27.5°

Refinement

Refinement on F2 R[F2 > 2(F2)] = 0.058 wR(F2) = 0.130 S = 1.34 1419 reflections 177 parameters H-atom parameters constrained w = 1/[2(Fo2) + (0.0826P)2] where P = (Fo2 + 2Fc2)/3 (/)max < 0.001 max = 0.97 e Å-3 min = -0.93 e Å-3 Extinction correction: SHELXL97 Extinction coefficient: 0.171 (13)

Table 1 Hydrogen-bond geometry (Å, °) D-HA D-H HA DA D-HA O1-H1N3i 0.82 1.94 2.742 (3) 167 O2-H2N1 0.82 1.90 2.711 (3) 173 N2-H2AO3 0.86 2.00 2.843 (3) 168 N2-H2BO2ii 0.86 2.56 3.229 (3) 135 C15-H15O3iii 0.93 2.55 3.181 (3) 126 Symmetry codes: (i) ; (ii) ; (iii) .

In the absence of significant anomalous scattering effects, Friedel pairs were averaged. All the H atoms were positioned geometrically (C-H = 0.93-0.96 Å, N-H = 0.86 Å and O-H = 0.82 Å) and refined as riding, with U_iso(H) = 1.2U_eq(carrier).

Data collection: DENZO (Otwinowski & Minor, 1997) and COLLECT (Hooft, 1998); cell refinement: DENZO and COLLECT; data reduction: DENZO and COLLECT; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 2003) and ORTEPII (Johnson, 1976); software used to prepare material for publication: PLATON.