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), C₅H₇N₃·C₆H₁₀N₂O₂, (I), and 2,6-diaminopyridine-theophylline (TEO; systematic name: 1,3-dimethyl-7H-purine-2,6-dione) (1/1), C₅H₇N₃·C₇H₈N₄O₂, (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 P2₁/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 R₂²(9) heterosynthon. A bidimensional supramolecular array is formed by interlinked DAP-TEO tetramers, producing a two-dimensional sheet.