A systematic study of the formation of pyridine-based supramolecular assemblies in the solid-state

The synthesis and subsequent investigation of the solid-state behaviour of functionalised pyridine dicarboxylate esters, has been undertaken. A number of these materials have shown a predisposal onto forming supramolecular tape-like assemblies, constructed via non-covalent interactions such at hydrogen bonding. The focus of this work is around four series of pyridine diesters (2,6-; 2,5-; 3,5-and 2,3-disubstituted), with a view to; (i) expanding the number of known tape assemblies and (ii) creating a library of homologous materials to permit cross reference between them. This was undertaken with the view to gaining insight into the factors that control these tape-like arrays’ primary (tape formation) and secondary (inter-tape) architecture. The solid-state structural investigation of these materials has principally employed single crystal X-ray diffraction with additional insight from structure analysis software such as Vista, Conquest, Mercury and Crystal Explorer. Further supporting information has been obtained through spectroscopic techniques such as MAS-NMR, Raman and DSC. The 2,6-materials, predicted by theory and are found experimentally to be superior at forming the extended tape-like arrays of interest. Structural evidence presented suggests that the 3,5-disubstituted diesters form weaker tape-like assemblies than their 2,6 disubstituted isomers, consistent with a weaker triple hydrogen bond contact than the former case. The 2,5-isomers also form tape-like assemblies but show different intermolecular contact patterns depending on the nature of the ester involved. Intramolecular steric clashes prevent the 2,3-isomers from adopting a planar conformation, this inhibits the formation of extended tape-like assemblies but provides insight into other competing intermolecular interactions possible in these molecules.