Different molecular conformations in the crystal structures of three 5-nitroimidazolyl derivatives

The crystal structures of (E)-1-methyl-5-nitro-1H-imidazole-2-carbaldehyde O-benzyl­oxime, C12H12N4O3, (I), (E)-1-methyl-5-nitro-1H-imidazole-2-carb­alde­hyde O-(4-fluoro­benz­yl) oxime, C12H11FN4O3, (II), and (E)-1-methyl-5-nitro-1H-imidazole-2-carbaldehyde O-(4-bromo­benz­yl) oxime, C12H11BrN4O3, (III), are described. The dihedral angle between the ring systems in (I) is 49.66 (5)° and the linking Nm—C—C=N (m = methyl­ated) bond shows an anti conformation [torsion angle = 175.00 (15)°]. Compounds (II) and (III) are isostructural [dihedral angle between the aromatic rings = 8.31 (5)° in (II) and 5.34 (15)° in (III)] and differ from (I) in showing a near-syn conformation for the Nm—C—C=N linker [torsion angles for (II) and (III) = 17.64 (18) and 8.7 (5)°, respectively], which allows for the occurrence of a short intra­molecular C—H...N contact. In the crystal of (I), C—H...N hydrogen bonds link the mol­ecules into [010] chains, which are cross-linked by very weak C—H...O bonds into (100) sheets. Weak aromatic π–π stacking inter­actions occur between the sheets. The extended structures of (II) and (III) feature several C—H...N and C—H...O hydrogen bonds, which link the mol­ecules into three-dimensional networks, which are consolidated by aromatic π–π stacking inter­actions. Conformational energy calculations and Hirshfeld fingerprint analyses for (I), (II) and (III) are presented and discussed.