2-Amino-4,6-dimethylpyrimidine–anthranilic acid (1/1)

In the title 1:1 adduct, C6H9N3·C7H7NO2, the crystal structure is stabilized by hydrogen bonds involving two different R 2 2(8) motifs. One of them is formed by the interaction of 2-amino-4,6-dimethylpyrimidine (AMPY) with the carboxyl group of anthranilic acid (AA) through N—H⋯O and O—H⋯N hydrogen bonds, whereas the other is formed through the interaction of two centrosymmetrically related pyrimidines involving N—H⋯N hydrogen bonds. These two combined motifs form a heterotetramer. The heterotetramer sheets are stacked into three-dimensional network.

In the title 1:1 adduct, C 6 H 9 N 3 ÁC 7 H 7 NO 2 , the crystal structure is stabilized by hydrogen bonds involving two different R 2 2 (8) motifs. One of them is formed by the interaction of 2-amino-4,6-dimethylpyrimidine (AMPY) with the carboxyl group of anthranilic acid (AA) through N-HÁ Á ÁO and O-HÁ Á ÁN hydrogen bonds, whereas the other is formed through the interaction of two centrosymmetrically related pyrimidines involving N-HÁ Á ÁN hydrogen bonds. These two combined motifs form a heterotetramer. The heterotetramer sheets are stacked into three-dimensional network.

Comment
The aminopyrimidine derivatives, in nature as components of nucleic acids, and drugs are relevant for biological functions.
Their interactions with carboxylic acids are of utmost importance since they are involved in protein -nucleic acid recognition and drug binding (Hunt et al.,1980;Baker & Santi, 1965). In general aminopyrimidines posses self complementary hydrogen-bonded motifs forming a base pair which in itself is an unique property. In addition, aminopyrimidines readily form pyrimidine-carboxylic acid interaction with ease which is evident from the survey carried out by Allen et al. (1999).
The asymmetric unit contains a molecule of AMPY and AA (Fig. 1). The N1 and the amino group of AMPY interact with the carboxyl group of AA via O-H···N and N-H···O hydrogen bonds (Table 1) generating ring motif with graph set notation R 2 2 (8). In addition, another type of R 2 2 (8) motif is formed by centrosmmetrically related pyrimidine molecules through a pair of N-H···N hydrogen bonds. These two different motifs generate a linear heterotetrameric unit ( Fig. 2) known to be one of the most stable synthons (Thakur & Desiraju, 2008).
One can expect similarity between the overall packing patterns of the title complex and 2-amino-4,6-dimethylpyrimidinesalicylate salt which has been earlier reported from our laboratory (Muthiah et al., 2006). The primary level of organization is similar in both structures as they form a linear heterotetrameric synthon. However, the planarity of the heterotetraameric synthons is different. The heterotetrameric synthon formed in AMPY-AA is planar whereas that of 2-amino-4,6-dimethylpyrimidinium salicylate salt is not planar. In the title complex heterotetramers are arranged as sheets ( Fig. 3) which are stabilized through stacking interactions. The same is also observed in the aminopyrimidine salicylate salt with two different types of sheets arranged alternatively one over the other.
AMPY forms stacking interactions with aromatic rings (Fig. 4) of the 2ABA molecules above and below its plane with perpendicular separations of 3.468 and 3.624 %A, respectively; centroid-to-centroid distances of 3.641 (7) and 3.934 (7)%A, offset distances of 1.130 and 1.858 %A and slip angles of 18.06 and 28.62, respectively. These geometric parameters are typical of aromatic stacking values (Hunter, 1994).

Experimental
A hot methanolic solution (20 ml) of 2-amino-4,6-dimethylpyrimidine (Aldrich) and anthranilic acid (Loba Chemie)in the ratio 1:1 was warmed for 0.5 h over a water bath. The mixture was cooled slowly and kept at room temperature and after a few days, colourless crystals were obtained.

Special details
Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell esds are taken into account in the estimation of distances, angles and tor-

sion angles
Refinement. Refinement on F 2 for ALL reflections except those flagged by the user for potential systematic errors. Weighted Rfactors wR and all goodnesses 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 observed criterion of F 2 > σ(F 2 ) is used only for calculating -R-factor-obs 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq