2-Amino-4,6-dimethoxypyrimidin-1-ium p-toluenesulfonate

In the title salt, C6H10N3O2 +·C7H7O3S−, the 2-amino-4,6-dimethoxypyrimidinium cation interacts with the sulfonate group of the p-toluenesulfonate anion via a pair of N—H⋯O hydrogen bonds, forming a cyclic hydrogen-bonded R 2 2(8) motif, which in the crystal is linked by further intemolecular N—H⋯O hydrogen bonds, forming supramolecular chains along the c axis. Furthermore, neighboring chains are interlinked via weak C—H⋯O hydrogen bonds and C—H⋯π interactions, forming layers.

In the title salt, C 6 H 10 N 3 O 2 + ÁC 7 H 7 O 3 S À , the 2-amino-4,6dimethoxypyrimidinium cation interacts with the sulfonate group of the p-toluenesulfonate anion via a pair of N-HÁ Á ÁO hydrogen bonds, forming a cyclic hydrogen-bonded R 2 2 (8) motif, which in the crystal is linked by further intemolecular N-HÁ Á ÁO hydrogen bonds, forming supramolecular chains along the c axis. Furthermore, neighboring chains are interlinked via weak C-HÁ Á ÁO hydrogen bonds and C-HÁ Á Á interactions, forming layers.
supplementary materials sup-1 Acta Cryst. (2011). E67, o2679-o2680 [ doi:10.1107/S160053681103755X ] 2-Amino-4,6-dimethoxypyrimidin-1-ium p-toluenesulfonate S. Gomathi and P. T. Muthiah Comment A study of non-covalent interactions, such as hydrogen bonding, plays a key role in molecular recognition and crystal engineering (Desiraju, 1989). Pyrimidines and aminopyrimidine derivatives are biologically important compounds and they manifest themselves in nature as components of nucleic acids. Some aminopyrimidine derivatives are used as antifolate drugs (Hunt et al., 1980;Baker & Santi, 1965). Their interactions with carboxylic acids are of utmost importance since they are involved in protein-nucleic acid recognition and drug-protein recognition processes, where the pyrimidine moiety of a drug forms hydrogen bonding with the carboxyl group of the protein. Aminopyrimidines readily pair up with carboxylic acids to form a wide variety of 1:1 adducts with mono and dicarboxylic acids (Etter & Adsmond, 1990). The R 2 2 (8) motif is a robust synthon which is frequently observed when a carboxylic acid interacts with a 2-amino heterocyclic ring system (Lynch & Jones, 2004). This motif is also recognized to be one of the top 5 motifs among the 24 commonly occurring motifs in crystal structures (Allen et al., 1998). In a sulfate-binding protein, the sulfate anion is bound mainly by seven hydrogen bonds, five of which are from the main chain peptide NH groups (Pflugrath & Quiocho, 1985;Jacobson & Quiocho, 1988).
Hydrogen bonding patterns involving sulfonate groups in biological systems and metal complexes are of current interest (Russell et al., 1994;Cai et al., 2001). Such interactions can be used for designing supramolecular architectures.
The crystal structures of 2-amino-4, 6-dimethoxy pyrimidine (Low et al., 2002) and p-toluene sulfonic acid monohydrate (Arora & Sundaralingam, 1971) have already been reported. Investigations of a fairly large number of crystal structure of 2-amino-4,6-dimethoxy/dimethyl pyrimidine salts and co crystals involving carboxylates (Thanigaimani et al., 2007;Thanigaimani et al., 2008;Ebenezer & Muthiah, 2010) and a few sulfonates (Balasubramani et al., 2007;Hemamalini et al., 2005) have already been reported from our laboratory. They reveal the formation of certain robust motifs and a variety of supramolecular architectures. A survey by Haynes et al. (2004) on the sulfonate salts, revealed various hydrogen bonding patterns and their preferences with specific functional groups. As part of our investigation to gain more insight into hydrogen bonding interactions involving aminopyrimidine and sulfonates, the crystal structure of title compound is presented herein.
This motif is further interlinked by an N-H···O hydrogen bond, involving 2-amino group of the 2-amino-4,6-dimethoxy pyrimidinium cation and O3 i (symmetry code: i -x,-y,-1/2 + z)) atom of p-toluenesulfonate anion to form a supramolecular supplementary materials sup-2 chain along the c axis (Fig. 2). The neighboring supramolecular chain is further interlinked via C-H···O hydrogen bond involving a methoxy group (C8) of cation and O5 ii (symmetry code: 1/2 -x, y, -1/2 + z) atom of sulfonate anion. Thus intermolecular hydrogen bonds generate a 2-D supramolecular network. The crystal structure is further stabilized by C-H··· π interaction. The C-H···π interaction is observed between the methoxy group (C7-H7A) of pyrimidinium cation with phenyl ring of p-toluenesulfonate anion (C-H···π = 3.7815 (18) Å, 145°). The identification of such supramolecular patterns will help us design and construct preferred hydrogen bonding patterns on drug like molecules.

Experimental
A hot ethanolic solution (20 ml) of 2-amino-4,6-dimethoxypyrimidine (38 mg, Aldrich) and p-toluene sulfonic acid (47 mg, Loba Chemie) was warmed for half an hour over a water bath. The mixture was cooled slowly and kept at room temperature; after a few days, colorless prismatic crystals were obtained.

Refinement
All hydrogen atoms were positioned geometrically and were refined using a riding model. The N-H and C-H bond lengths are 0.86 and 0.93-0.96 Å, respectively [U iso (H)=1.2-1.5U eq (parent atom)]. Fig. 1. The asymmetric unit of (I), showing 30% probability displacement ellipsoids. Dashed lines indicate hydrogen bonds.