Cocrystals of pyrazine and benzene polycarboxylic acids.

Abstract

The crystal structures of four cocrystals of pyrazine with benzene polycarboxylic acids were determined, namely pyrazine-phthalic (benzene-1,2-dicarboxylic) acid (1/1), C4H4N2·C8H6O4 (1), pyrazine-hemimellitic (benzene-1,2,3-tricarboxylic) acid (1/1), C4H4N2·C9H6O6 (2), pyrazine-hemimellitic acid-water (1/2/2), C4H4N2·2C9H6O6·2H2O (2a), and pyrazine-pyromellitic (benzene-1,2,4,5-tetracarboxylic) acid (3/1), 3C4H4N2·C10H6O8 (3). In all cases, infinite chains of alternating acid and base molecules, bonded by O-H...N hydrogen bonds, are formed. However, the details of the supramolecular structures are different. The additional carboxylic acid groups in the tri- and tetracarboxylic acids participate in hydrogen bonding with neighbouring acid molecules (in 2), water molecules, which makes the structure more complicated (in 2a), or with additional pyrazine molecules (in 3). π-π interactions between aromatic rings help organize the crystal architectures in all cases except for hydrate 2a. In that case, the hydrogen-bond-enriched structure enforces a disposition of the rings in which no stacking is observed. The Hirshfeld surface analysis allows better visualization of the differences between the structures by fingerprint plots in particular.