Patterns of hydrogen bonding in mono- and di-substituted N-arylpyrazinecarboxamides

Abstract

The molecular and supramolecular structures of 18 N-arylpyrazinecarboxamides, Ar NHCO(C4H3N2), have been determined, including the stoichiometric monohydrate of N-(3-methoxyphenyl)pyrazinecarboxamide, and two polymorphs of N-(4-fluorophenyl)pyrazinecarboxamide having Z′ values of 1 and 4, respectively. The aryl groups were selected to include the geometric isomers for a compact range of substituents, namely methyl, trifluoromethyl, fluoro, chloro, methoxy and nitro groups, which exhibit markedly varied electronic properties and markedly varied behaviour as hydrogen-bond donors and acceptors. However, not all isomers in each group could be structurally investigated. A small number of derivatives containing disubstituted aryl groups have also been included in this study. The crystal structures of the solvent-free carboxamides reported here exhibit a wide range of direction-specific intermolecular forces, including N—H...N, N—H...O, C—H...N and C—H...O hydrogen bonds, and π...π stacking interactions, while the structure of N-(3-methoxyphenyl)pyrazinecarboxamide monohydrate also contains O—H...N and O—H...O hydrogen bonds. The resulting supramolecular structures can be zero-, one- or two-dimensional, although no three-dimensional supramolecular aggregation has been observed. In the finite, zero-dimensional structures, pairs of molecules are linked by hydrogen bonds to form cyclic centrosymmetric dimers. The one-dimensional structures include chains formed by the π-stacking of otherwise isolated molecules, simple chains generated by either C—H...O or C—H...N hydrogen bonds, and hydrogen-bonded chains of rings. The two-dimensional structures include examples of both π-stacked hydrogen-bonded chains and hydrogen-bonded sheets.