Patterns of hydrogen bonding in mono- and disubstituted N-arylpyrazinecarboxamides

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 center dot center dot center dot N, N-H center dot center dot center dot O, C-H center dot center dot center dot N and C-H center dot center dot center dot O hydrogen bonds, and pi...pi stacking interactions, while the structure of N-(3-methoxyphenyl) pyrazinecarboxamide monohydrate also contains O-H center dot center dot center dot N and O-H center dot center dot center dot 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 pi-stacking of otherwise isolated molecules, simple chains generated by either C-H center dot center dot center dot O or C-H center dot center dot center dot N hydrogen bonds, and hydrogen-bonded chains of rings. The two-dimensional structures include examples of both pi-stacked hydrogen-bonded chains and hydrogen-bonded sheets.