Creation of ternary multicomponent crystals by exploitation of charge-transfer interactions

Four new ternary crystalline molecular complexes have been synthesised from a common 3,5-dinitrobenzoic acid (3,5-dnda) and 4,4'-bipyridine (bipy) pairing with a series of amino-substituted aromatic compounds (4-aminobenzoic acid (4-aba), 4-(N,N-dimethylamino)benzoic acid (4-dmaba), 4-aminosalicylic acid (4-asa) and sulfanilamide (saa)). The ternary crystals were created through the application of complementary charge transfer and hydrogen-bonding interactions. For these systems a dimer was created through a charge-transfer interaction between two of the components, while hydrogen bonding between the third molecule and this dimer completed the construction of the ternary co-crystal. All resulting structures display the same acid⋅⋅⋅pyridine interaction between 3,5-dnba and bipy. However, changing the third component causes the proton of this bond to shift from neutral OH⋅⋅⋅N to a salt form, O(-) ⋅⋅⋅HN(+) , as the nature of the group hydrogen bonding to the carboxylic acid was changed. This highlights the role of the crystal environment on the level of proton transfer and the utility of ternary systems for the study of this process.