Two series of a total of ten cocrystals involving 4-amino-5-chloro-2,6-dimethylpyrimidine with various carboxylic acids have been prepared and characterized by single-crystal X-ray diffraction. The pyrimidine unit used for the cocrystals offers two ring N atoms (positions N1 and N3) as proton-accepting sites. Depending upon the site of protonation, two types of cations are possible [Rajam et al. (2017). Acta Cryst. C73, 862–868]. In a parallel arrangement, two series of cocrystals are possible depending upon the hydrogen bonding of the carboxyl group with position N1 or N3. In one series of cocrystals, i.e. 4-amino-5-chloro-2,6-dimethylpyrimidine–3-bromothiophene-2-carboxylic acid (1/1), 1, 4-amino-5-chloro-2,6-dimethylpyrimidine–5-chlorothiophene-2-carboxylic acid (1/1), 2, 4-amino-5-chloro-2,6-dimethylpyrimidine–2,4-dichlorobenzoic acid (1/1), 3, and 4-amino-5-chloro-2,6-dimethylpyrimidine–2-aminobenzoic acid (1/1), 4, the carboxyl hydroxy group (–OH) is hydrogen bonded to position N1 (O—H...N1) of the corresponding pyrimidine unit (single point supramolecular synthon). The inversion-related stacked pyrimidines are doubly bridged by the carboxyl groups via N—H...O and O—H...N hydrogen bonds to form a large cage-like tetrameric unit with an R
4
2(20) graph-set ring motif. These tetrameric units are further connected via base pairing through a pair of N—H...N hydrogen bonds, generating R
2
2(8) motifs (supramolecular homosynthon). In the other series of cocrystals, i.e. 4-amino-5-chloro-2,6-dimethylpyrimidine–5-methylthiophene-2-carboxylic acid (1/1), 5, 4-amino-5-chloro-2,6-dimethylpyrimidine–benzoic acid (1/1), 6, 4-amino-5-chloro-2,6-dimethylpyrimidine–2-methylbenzoic acid (1/1), 7, 4-amino-5-chloro-2,6-dimethylpyrimidine–3-methylbenzoic acid (1/1), 8, 4-amino-5-chloro-2,6-dimethylpyrimidine–4-methylbenzoic acid (1/1), 9, and 4-amino-5-chloro-2,6-dimethylpyrimidine–4-aminobenzoic acid (1/1), 10, the carboxyl group interacts with position N3 and the adjacent 4-amino group of the corresponding pyrimidine ring via O—H...N and N—H...O hydrogen bonds to generate the robust R
2
2(8) supramolecular heterosynthon. These heterosynthons are further connected by N—H...N hydrogen-bond interactions in a linear fashion to form a chain-like arrangement. In cocrystal 1, a Br...Br halogen bond is present, in cocrystals 2 and 3, Cl...Cl halogen bonds are present, and in cocrystals 5, 6 and 7, Cl...O halogen bonds are present. In all of the ten cocrystals, π–π stacking interactions are observed.
Study of the Halogen Bonding between Pyridine and Perfluoroalkyl Iodide in Solution Phase Using the Combination of FTIR and 19F NMR
