Hydrogen-bonding and p±p inter- actions in 2-amino-4,6-dimethyl- pyrimidinium salicylate Packianathan Thomas Muthiah, a * Kasthuri Balasubramani, a Urszula Rychlewska b and Agnieszka Plutecka b a School of Chemistry, Bharathidasan University, Tiruchirappalli 620 024, Tamilnadu, India, and b Department of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, 60-780 Poznan  , Poland Correspondence e-mail: tommtrichy@yahoo.co.in Received 16 May 2006 Accepted 7 August 2006 Online 12 September 2006 In the crystal structure of the title compound, C 6 H 10 N 3 + C 7 H 5 O 3  , the asymmetric unit contains four crystal- lographically independent 2-amino-4,6-dimethylpyrimidinium and salicylate ions (Z = 8). In each of these, one of the pyrimidine N atoms is protonated, and the carboxylate group of the salicylate ion interacts with the pyrimidine group through a pair of NÐHO hydrogen bonds, forming an R 2 2 (8) motif. The pyrimidine cations also form base pairs via a pair of NÐHN hydrogen bonds (involving the amino group and the unprotonated ring N atom), forming another R 2 2 (8) motif. Three such R 2 2 (8) motifs, fused together, constitute a closed cyclic aggregate, and the linking of these aggregates, arranged in consecutive layers, can be analysed in terms of off-face stacking interactions. Comment The hydrogen-bonding patterns, including base pairing, formed by aminopyrimidines, and base stacking, are important in nucleic acid structures and their functions. Some amino- pyrimidine derivatives are used as antifolate drugs (Hunt et al., 1980; Baker & Santi, 1965). 2-Aminopyrimidine and its deri- vatives are of particular interest as adduct formers because of their ability to form stable hydrogen-bonded chains via their stereochemically associated amine group and the ring N atoms (Lynch et al., 2000; Lynch & Jones, 2004). Salicylic acid is a widely used analgesic. The crystal structures of amino- pyrimidine derivatives (Schwalbe & Williams, 1982), amino- pyrimidine carboxylates (Hu et al., 2002) and cocrystal structures (Chinnakali et al., 1999) have been reported. The crystal structure of 2-amino-4,6-dimethylpyrimidinium bromide 2-amino-4,6-dimethylpyrimidine monohydrate (Pan- neerselvam et al., 2004), 2-amino-4,6-dimethylpyrimidinium hydrogen sulfate (Hemamalini et al., 2005), bis(2,4-diamino-6- oxopyrimidinium) sulfate monohydrate (Muthiah et al., 2004) and 2-amino-4,6-dimethylpyrimidine±cinnamic acid (1/2) (Balasubramani et al., 2005) have recently been reported from our laboratory. The present study is aimed at investigating the supramolecular interactions of the title compound, (I). The asymmetric unit of (I) consists of four crystal- lographically independent 2-amino-4,6-dimethylpyrimidinium cations and salicylate anions, as shown in Fig. 1. The consti- tuent atoms of all four ionic pairs have been labelled in an identical manner, except that the individual molecules are identi®ed by the suf®x A, B, C or D. Protonation of the pyrimidine base on the N1 site is re¯ected in a change in bond organic compounds Acta Cryst. (2006). C62, o605±o607 DOI: 10.1107/S0108270106031015 # 2006 International Union of Crystallography o605 Acta Crystallographica Section C Crystal Structure Communications ISSN 0108-2701 Figure 1 A molecular drawing of the asymmetric unit of (I), showing 50% probability displacement ellipsoids and the atom-numbering scheme. H atoms have been omitted for clarity.