Malonic acid (1:1) 2-aminopyridine molecular complex: crystal structure and hirshfeld surface analysis

Co-crystallization is the supramolecular combination of two or more different chemical entities in a crystalline lattice through non-covalent interactions. In particular, the preparation of pharmaceutical co-crystals offers a means to modify the physicochemical properties of crystals without altering the chemical properties of a pharmaceutical molecule, improving several physical properties of the pure drug such as solubility, bioavailability, thermal stability, etc. This work shows a good example of synthesis and characterization of a cocrystal which can contribute to the pharmaceutical industry. In this study, single-crystal X-ray diffraction was used to characterize structurally the molecular complex formed between two pharmaceutical conformers; 2-aminopyridine and malonic acid. The title compound has been synthesized by grinding in an agate mortar. Its structure was characterized by X-ray diffraction. This compound crystallize in the monoclinic system with space group P21/n, Z = 4, and unit cell parameters a = 7.718(1) A, b = 17.518(2) A, c = 13.726(2) A, = 94.270(8)°, V = 1850.6(4) A3. The salt, C3H3O4 -·C5H7N2 +, is an ionic ensemble assisted by hydrogen bonds established between malonate anions and 2-aminopyridinium cations. The two components thus construct a supramolecular assembly with a three-dimensional hydrogen bonded framework. Hirshfeld surface analysis was used for visually analyzing intermolecular interactions in the crystal structure.