Conformational polymorphism of the molecular complex of 3-fluorobenzoic acid with 4-acetylpyridine

Thomas, L. H., Craig, G. A., Gutmann, M. J., Parkin, A., Shankland, K. ORCID: https://orcid.org/0000-0001-6566-0155 and Wilson, C. C. (2011) Conformational polymorphism of the molecular complex of 3-fluorobenzoic acid with 4-acetylpyridine. CrystEngComm, 13 (10). pp. 3349-3354. ISSN 1466-8033 doi: 10.1039/c1ce05139c

Abstract/Summary

Two polymorphs of the molecular complex formed between 3-fluorobenzoic acid with 4-acetylpyridine are described and found to be based upon the same dimeric supramolecular construct. The conformational freedom around the hydrogen bond results in a 180 degrees rotation about this intermolecular link, distinguishing the polymorphs and affecting the packing of the dimeric units. The two polymorphs are fully characterised by single crystal X-ray and neutron diffraction and quantum mechanical calculations. There is evidence of structured crystal growth defects in both polymorphic crystals via observation of diffuse scattering and a disorder model for the average structure of Form I, which can be interpreted as a mixing of the two dimer conformations. The similarity of energy of the distinct dimeric units, supporting their likely co-existence, has been verified by periodic quantum chemical calculations.