Crystal structure of pharmaceutical cocrystals of 2,6-diaminopyridine with piracetam and theophylline

Pharmaceutical cocrystals are crystalline solids formed by an active pharmaceutical ingredient and a cocrystal former. The cocrystals 2,6-diaminopyridine (DAP)–piracetam [PIR; systematic name: 2-(2-oxopyrrolidin-1-yl)acetamide] (1/1), C 5 H 7 N 3 ·C 6 H 10 N 2 O 2 , (I), and 2,6-diaminopyridine–theophylline (TEO; systematic name: 1,3-dimethyl-7 H -purine-2,6-dione) (1/1), C 5 H 7 N 3 ·C 7 H 8 N 4 O 2 , (II), were prepared by the solvent-assisted grinding method and were characterized by IR spectroscopy and powder X-ray diffraction. Cocrystal (I) crystallized in the orthorhombic space group Pbca and showed a 1:1 stoichiometry. The DAP and PIR molecules are linked by an N—H...O hydrogen-bond interaction. Self-assembly of PIR molecules forms a sheet of C (4) and C (7) chains. Cocrystal (II) crystallized in the monoclinic P 2 1 / c space group and also showed a 1:1 stoichiometry. The DAP and TEO molecules are connected by N—H...N and N—H...O hydrogen bonds, forming an R 2 2 (9) heterosynthon. A bidimensional supramolecular array is formed by interlinked DAP–TEO tetramers, producing a two-dimensional sheet.