The co-crystallisation of pyridine with benzenepolycarboxylic acids: The interplay of strong and weak hydrogen bonding motifs

Co-crystallisation of pyridine with terephthalic, trimesic, phthalic, isophthalic and pyromellitic acids has been investigated via single crystal X-ray diffraction and thermogravimetric analysis, concentrating on the nature of the intermolecular interactions. The five new compounds are terephthalic acid bis(pyridine) solvate, trimesic acid tris(pyridine) solvate, pyridinium hydrogen phthalate, isophthalic acid pyridine solvate and pyridinium trihydrogen pyromellitate. A variety of supramolecular hydrogen bonded motifs involving interactions between pyridine molecules and carboxylic acid groups are observed rather than just the R22(7) O–H⋯N/C–H⋯O motif; while the common carboxylic acid head-to-tail ring motif is absent in all of the examples investigated. TGA analysis of pyridine loss from two of the compounds has been shown to correlate with the strength of hydrogen bonds in the crystal structures.