Co-crystal formation between 2,2′-dithiodibenzoic acid and each of 4,4′-bipyridine, trans-1,2-bis(4-pyridyl)ethene and 1,2-bis(4-pyridyl)ethane

The results of crystallographic analyses on a series of 1 ∶ 1 and 2 ∶ 1 co-crystals formed between 2,2′-dithiodibenzoic acid (DTBA) and each of 4,4′-bipyridine, trans-1,2-bis(4-pyridyl)ethene and 1,2-bis(4-pyridyl)ethane are described. Neutral molecules connected via O–H⋯N hydrogen-bonds leading to chains are found in the 1 ∶ 1 co-crystals. The intervention of a lattice water in a pseudo-polymorph of DTBA ∶ 1,2-bis(4-pyridyl)ethane consolidates chains into a 2-D array. Proton transfer occurs in the 2 ∶ 1 co-crystals so that the predominant motifs are chains of DTBA anions connected via charge-assisted O–H⋯O− interactions. In the co-crystal formed between 2(DTBA) ∶ 4,4′-bipyridine, characterised as a monohydrate, layers comprising DTBA anions are interspersed with layers of bipyridinium cations connected by water molecules. In the 2(DTBA) ∶ trans-1,2-bis(4-pyridyl)ethene and 2(DTBA) ∶ 1,2-bis(4-pyridyl)ethane co-crystals, the layers of DTBA anions are connected via O–H⋯O hydrogen-bonds and define columns in which are threaded chains of bipyridinium cations connected via N–H⋯N+ hydrogen-bonding. Finally, in the pseudopolymorph, 2(DTBA) ∶ 1,2-bis(4-pyridyl)ethane.EtOH, layers of anions are bridged by bipyridinium cations so that rectangular columns are defined and in which the solvent ethanol molecules reside.