title: Patterns of hydrogen bonding in mono- and di-substituted N-arylpyrazinecarboxamides.
abstract: The molecular and supramolecular structures of 18 N-arylpyrazinecarboxamides, Ar NHCO(C(4)H(3)N(2)), 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 pi...pi 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 pi-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 pi-stacked hydrogen-bonded chains and hydrogen-bonded sheets.
authors.affiliation: Fundação Oswaldo Cruz, Far Manguinhos, Rua Sizenando Nabuco, 100 Manguinhos, 21041-250 Rio de Janeiro, RJ, Brazil.
authors.forename: Solange M S V
authors.initials: SM
authors.lastname: Wardell
authors.forename: Marcus V N
authors.initials: MV
authors.lastname: de Souza
authors.forename: Thatyana R A
authors.initials: TR
authors.lastname: Vasconcelos
authors.forename: Marcelle de L
authors.initials: Mde L
authors.lastname: Ferreira
authors.forename: James L
authors.initials: JL
authors.lastname: Wardell
authors.forename: John N
authors.initials: JN
authors.lastname: Low
authors.forename: Christopher
authors.initials: C
authors.lastname: Glidewell