Abstract
X-ray analysis of N-(4-fluorophenyl)-1,5-dimethyl-1H-imidazole-4-carboxamide 3-oxide reveals the temperature-dependent polymorphism associated with the crystallographic symmetry conversion. The observed crystal structure transformation corresponds to a symmetry reduction from I41 /a (I) to P43 (II) space groups. The phase transition mainly concerns the subtle but clearly noticeable reorganization of molecules in the crystal space, with the structure of individual molecules left almost unchanged. The Hirshfeld surface analysis shows that various intermolecular contacts play an important role in the crystal packing, revealing graphically the differences in spatial arrangements of the molecules in both polymorphs. The N-oxide oxygen atom acts as a formally negatively charged hydrogen bonding acceptor in intramolecular hydrogen bond of N–H…O− type. The combined crystallographic and theoretical DFT methods demonstrate that the observed intramolecular N-oxide N–H…O hydrogen bond should be classified as a very strong charge-assisted and closed-shell non-covalent interaction.
Highlights
Research on new imidazole and benzimidazole N-oxides and their applications in biology has focused particular interest in recent years [1]
We report the results of X-ray crystal structure determination of N-(4-fluorophenyl)-1,5-dimethyl-1H-imidazole-4-carboxamide 3-oxide polymorphs (Scheme 1)
The observed phenomenon is defined as a reversible order–disorder–order phase conversion associated with the lowering of crystallographic symmetry
Summary
Research on new imidazole and benzimidazole N-oxides and their applications in biology has focused particular interest in recent years [1]. Special attention was paid to the synthesis of imidazole N-oxides with new substitution patterns, the analogs lacking a substituent at carbon C(2) atom, and their transformations into more complex derivatives [5, 7,8,9]. We turned our attention to derivatives bearing hydrogen donor groups at the vicinal C(4) position, namely amide [10, 11] and hydrazide [12, 13] moieties. The presence of such groups and stable N-oxide function offers an opportunity for their application in more complex structures including biologically active compounds and enables carrying out the reactions under harsh conditions. Some reports on imidazole derivatives containing amide or Struct Chem (2014) 25:979–989
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