Temperature-dependent polymorphism of N-(4-fluorophenyl)-1,5-dimethyl-1H-imidazole-4-carboxamide 3-oxide: experimental and theoretical studies on intermolecular interactions in the crystal state

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 I4 1 /a (I) to P4 3 (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.

Non-covalent interactions of N-phenyl-1,5-dimethyl-1H-imidazole-4-carboxamide 3-oxide derivatives—a case of intramolecular N-oxide hydrogen bonds

“…The ranges of geometrical parameters in the analyzed crystal structures are in agreement with that observed for the previously studied N-(4-fluorophenyl)-1,5-dimethyl-1H-imidazole-4-carboxamide 3-oxide [19]. All of the investigated molecules consist of three characteristic fragments: the phenyl ring (C8, C9, C10, C11, C12,C13-Ph plane) substituted at position 4 in compounds II-VI, a carboxamide bridge (C5, C6, O6, N7,C8-Carboxam plane), and an imidazole ring (N1, C2, N3, C4, C5-Im plane) substituted by two methyl groups.…”

“…Our recent studies have shown that the N-oxide group may act as an effective proton acceptor in hydrogen bonding [17][18][19]. Also, in case of the crystal structures investigated here, the Noxide group contributes to these kinds of interaction.…”

“…Recently, the N-oxide group has been the subject of our studies in the context of its ability to act as an electron donor in various types of intermolecular interactions [17][18][19]. Various N-oxide interactions stabilizing crystal structures have been investigated [17].…”

“…The corresponding energy value for (H 3 C) 2 O and H 2 C=O molecules as oxygen proton acceptors is of about half of that, ∼7 and ∼9 kcal/mol, respectively. Interestingly, we recently found that imidazole N-oxide is able to interact with proton donors not only in strong intermolecular but also in intramolecular hydrogen bonds with energies of about 12 kcal/mol [19].…”

“…The previously obtained results caused our attention to turn to intramolecular interactions [19]. For the purpose of more detailed description of this kind of hydrogen bonding, a series of N-phenyl-1,5-dimethyl-1H-imidazole-4-carboxamide 3-oxide derivatives were synthesized according to a procedure described elsewhere [20][21][22] and analyzed by means of crystal X-ray diffraction methods.…”