Structural comparisons between methylated and unmethylated nitrophenyl lophines.
The lophine derivative 2-(2-nitrophenyl)-4,5-diphenyl-1H-imidazole, C21H15N3O2, (I), crystallized from ethanol as a solvent-free crystal and from acetonitrile as the monosolvate, C21H15N3O2.C2H3N, (II). Crystallization of 2-(4-nitrophenyl)-4,5-diphenyl-1H-imidazole from methanol yielded the methanol monosolvate, C21H15N3O2.CH4O, (III). Three lophine derivatives of methylated imidazole, namely, 1-methyl-2-(2-nitrophenyl)-4,5-diphenyl-1H-imidazole methanol solvate, C22H17N3O2.CH4O, (IV), 1-methyl-2-(3-nitrophenyl)-4,5-diphenyl-1H-imidazole, C22H17N3O2, (V), and 1-methyl-2-(4-nitrophenyl)-4,5-diphenyl-1H-imidazole, C22H17N3O2, (VI), were recrystallized from methanol, acetonitrile and ethanol, respectively, but only (IV) produced a solvate. Compounds (III) and (IV) each crystallize with two independent molecules in the asymmetric unit. Five imidazole molecules in the six crystals differ in their molecular conformations by rotation of the aromatic rings with respect to the central imidazole ring. In the absence of a methyl group on the imidazole [compounds (I)-(III)], the rotation angles are not strongly affected by the position of the nitro group [44.8 (2) and 45.5 (1) degrees in (I) and (II), respectively, and 15.7 (2) and 31.5 (1) degrees in the two molecules of (III)]. However, the rotation angle is strongly affected by the presence of a methyl group on the imidazole [compounds (IV)-(VI)], and the position of the nitro group (ortho, meta or para) on a neighbouring benzene ring; values of the rotation angle range from 26.0 (1) [in (VI)] to 85.2 (1) degrees [in (IV)]. This group repulsion also affects the outer N-C-N bond angle. The packing of the molecules in (I), (II) and (III) is determined by hydrogen bonding. In (I) and (II), molecules form extended chains through N-H...N hydrogen bonds [with an N...N distance of 2.944 (5) A in (I) and 2.920 (3) A in (II)], while in (III) the chain is formed with a methanol solvent molecule as the mediator between two imidazole rings, with O...N distances of 2.788 (4)-2.819 (4) A. In the absence of the imidazole N-H H-atom donor, the packing of molecules (IV)-(VI) is determined by weaker intermolecular interactions. The methanol solvent molecule in (IV) is hydrogen bonded to imidazole [O...N = 2.823 (4) A] but has no effect on the packing of molecules in the unit cell.
Yanover
Diana
D
Schulich Faculty of Chemistry, Technion-Israel Institute of Technology, Haifa 32000, Israel.
Kaftory
Menahem
M