A study of supramolecular hydrogen bonded complexes formed by aliphatic dicarboxylic acids with azaaromatic donors

Crystal structures of the hydrogen bonded, 1:1 molecular complexes of malonic, glutaric, adipic, thiodiglycolic and thiodipropionic acids with 4,4′-bipyridyl have been investigated in detail. All the dicarboxylic acids form molecular tape-like structures, but thiodiglycolic acid gives a cyclic structure, favoured by intermolecular π- π interaction between the heteroatom-rings. The cyclic structure is indeed unique, in the sense that it represents a noncovalent synthesis of a rectangle. Crystal structures of hydrogen bonded molecular complexes of malonic, succinic, glutaric, adipic and thiodipropionic acids with 2,4,6-triaminopyrimidine have been studied. By and large, only tape-like structures are formed, the crossed ribbon network being favoured in the complexes of malonic and glutaric acids with an odd number carbon atoms. In all the complexes of 2,4,6-triaminopyrimidine, proton transfer occurs from the carboxyl group to the heteroatom nitrogen, giving rise to a strong hydrogen bonded cyclic system.