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Salts and cocrystals of chloranilic acid with organic bases : is it possible to predict a proton transfer in a crystal?

On supramolecular chemistry grounds proton-donor (chloranilic acid) and acceptor (organic bases) were combined to generate multi-component hydrogen bonded systems. Two steps of deprotonation of chloranilic acid lead to monoanion and dianion. Accordingly, dissociation of chloranilic acid can be accompanied by a proton transfer from acid to an organic base. Thus, a series of salts with organic bases such as dimethylamine, 2-methylpyridine, 2, 6-dimethyl-4-amino-pyrimidine, and R, S-tryptophane were prepared and their crystal structures determined. The cocrystals of neutral chloranilic acid with 5, 6-phenantroline were obtained, also. In the crystal packing of these multicomponent systems predominant interactions are hydrogen bonds. According to the topology of hydrogen bonds seven distinctive motifs can be recognized ; basic structural units are either dimeric monoanions of chloranilic acid or monomeric dianions, and monomers of neutral acid. Due to the presence of protonated bases the dominant interaction is N+– H• • • O hydrogen bond. Stereochemical parameters of bases influence the topology leading to the formation of discrete motifs or chains.

chloranilic acid ; organic bases ; multicomponent crystals ; proton transfer ; pKa ; hydrogen bonding topology ; π • • • π interaction

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