Crystal structures of 1-hydroxylimidazole and imidazole 1-oxide derivatives

The N-oxcide or 1-hydroxy forms of four solid 1-hydroxy-5-(4-methyl-2-nitroimidazol-2-yl)-4-phenyl-2-(X-phenyl)-imidazole derivatives, 6, have been studied by X-ray crystallography: Compounds, (6: X=4-Br) and (6: X=2-O2N), both recrystallized from EtOH, and (6: X=4-F), recrystallized from EtOCH2CH2OH, were isolated in the 1-hydroxyimidazole form. In contrast, (6: X=H), recrystallized from EtOCH2CH2OH, was obtained in the imidazole N-oxide form. Two independent molecules, Mol A and Mol B, rotamers, are present in the asymmetric unit of the imidazole N-oxide compound, (6: X=H) and are linked into chains of alternating compounds, mainly by N-H center dot center dot center dot O hydrogen bonds, but also by N-H center dot center dot center dot N and C-H center dot center dot center dot O hydrogen bonds and pi center dot center dot center dot pi interactions. These chains are linked by other C-H center dot center dot center dot O and C-H center dot center dot center dot N hydrogen bonds and pi center dot center dot center dot pi interactions into a 3-D arrangement. In the 1-hydroxyimidazole compound, (6: X=2-O2N), classical hydrogen bonds, O1-H1 center dot center dot center dot N3, are the major interactions linking molecules into C(5) chains: weak pi center dot center dot center dot pi stacking interactions also link the molecules within the chains. These chains are linked by C-H center dot center dot center dot O and hydrogen bonds and by N-O center dot center dot center dot pi interactions into a three- dimensional array. The other 1-hydroxyhnidazole compounds, (6: X=4-Br) and (6: X=4-F), have similar structures, which differ from that of (6: X=2-O2N). In (6: X=4-Br) and (6: X=4-F), pairs of classical O-H center dot center dot center dot N hydrogen bonds link molecules into symmetric dimers: these dimers are further stabilized by pi center dot center dot center dot pi interactions. Other intermolecular interactions found in both (6: X=4-Br) and (6: X=4-F) are C-H center dot center dot center dot O hydrogen bond and N-O center dot center dot center dot pi interactions, which link the O-H center dot center dot center dot N hydrogen bonded dimers into a 3-dimensional array.