Cocrystals of pyrazine and benzene polycarboxylic acids

The crystal structures of four cocrystals of pyrazine with benzene polycarboxylic acids were determined, namely pyrazine–phthalic (benzene‐1,2‐dicarboxylic) acid (1/1), C 4 H 4 N 2 ·C 8 H 6 O 4 ( 1 ), pyrazine–hemimellitic (benzene‐1,2,3‐tricarboxylic) acid (1/1), C 4 H 4 N 2 ·C 9 H 6 O 6 ( 2 ), pyrazine–hemimellitic acid–water (1/2/2), C 4 H 4 N 2 ·2C 9 H 6 O 6 ·2H 2 O ( 2a ), and pyrazine–pyromellitic (benzene‐1,2,4,5‐tetracarboxylic) acid (3/1), 3C 4 H 4 N 2 ·C 10 H 6 O 8 ( 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.