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 th e 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 hydrog en bonding network for this molecule both in condensed state and solution. Furthermore, a novel extended hydrogen bonding graph-set has been derived f or this molecule in crystalline state. Comparison of pyridine-2,6-dicarboxa mide with 1,3-benzenedicarboxamide, where the intramolecular hydrogen bondi ng to the pyridine ring in the former has been removed, yields a different intermolecular hydrogen bonded structure in the solid state. A new graph-se t has been determined for the extended structure of 1,3-benzenedicarboxamid e in the solid state. In solution, 1,3-benzenedicarboxamide is shown to mai ntain a hydrogen bonding pattern that is weaker than that observed with pyr idine-2,6-dicarboxamide. Replacement of one hydrogen on each carboxamide ni trogen of pyridine-2,6-dicarboxamide by a methyl group also alters the exte nded structure to a significant extent. In N,N'-dimethyl-2,6-pyridinedicarb oxamide, the three-dimensional hydrogen bending pattern observed with pyrid ine-2,6-dicarboxamide all but collapses to one-dimensional chains. (C) 2000 Elsevier Science B.V. All rights reserved.