Extended structures controlled by intramolecular and intermolecular hydrogen bonding:: a case study with pyridine-2,6-dicarboxamide, 1,3-benzenedicarboxamide and N,N′-dimethyl-2,6-pyridinedicarboxamide

The small organic molecule pyridine-2,6-dicarboxamide, although known in the literature for some time, exhibits interesting and previously unexplored intermolecular and intramolecular hydrogen bonding both in solid state and in solution. With the aid of X-ray crystallography and variable-temperature NMR spectroscopy, we here demonstrate the presence of a very strong hydrogen bonding network for this molecule both in condensed state and solution. Furthermore, a novel extended hydrogen bonding graph-set has been derived for this molecule in crystalline state. Comparison of pyridine-2,6-dicarboxamide with 1,3-benzenedicarboxamide, where the intramolecular hydrogen bonding to the pyridine ring in the former has been removed, yields a different intermolecular hydrogen bonded structure in the solid state. A new graph-set has been determined for the extended structure of 1,3-benzenedicarboxamide in the solid state. In solution, 1,3-benzenedicarboxamide is shown to maintain a hydrogen bonding pattern that is weaker than that observed with pyridine-2,6-dicarboxamide. Replacement of one hydrogen on each carboxamide nitrogen of pyridine-2,6-dicarboxamide by a methyl group also alters the extended structure to a significant extent. In N,N'-dimethyl-2,6-pyridinedicarboxamide, the three-dimensional hydrogen bending pattern observed with pyridine-2,6-dicarboxamide all but collapses to one-dimensional chains. (C) 2000 Elsevier Science B.V. All rights reserved.