Involvement of conformational isomerism in the complexity of the crystal network of 1-(4-nitrophenyl)-1 H -1,3-benzimidazole derivatives driven by C—H... A ( A = NO 2 , N py and π) and orthogonal N py ...NO 2 and ONO...C sp 2 interactions

A detailed structural analysis of the benzimidazole nitroarenes 1-(4-nitrophenyl)-1 H -1,3-benzimidazole, C 13 H 9 N 3 O 2 , (I), 1-(4-nitrophenyl)-2-phenyl-1 H -1,3-benzimidazole, C 19 H 13 N 3 O 2 , (II), and 2-(3-methylphenyl)-1-(4-nitrophenyl)-1 H -1,3-benzimidazole, C 20 H 15 N 3 O 2 , (III), has been performed. They are nonplanar structures whose crystal arrangement is governed by C sp 2 —H... A ( A = NO 2 , N py and π) hydrogen bonding. The inherent complexity of the supramolecular arrangements of compounds (I) ( Z ′ = 2) and (II) ( Z ′ = 4) into tapes, helices and sheets is the result of the additional participation of π–{\pi}_{{\rm NO}_2}} and n –π* ( n = O and N py ; π* = C sp 2 and {\rm N}_{{\rm NO}_2}}) interactions that contribute to the stabilization of the equi-energetic conformations adopted by each of the independent molecules in the asymmetric unit. In contrast, compound (III) ( Z ′ = 1) is self-paired, probably due to the effect of the steric demand of the methyl group on the crystal packing. Theoretical ab initio calculations confirmed that the presence of the arene ring at the benzimidazole 2-position increases the rotational barrier of the nitrobenzene ring and also supports the electrostatic nature of the orthogonal ONO...C sp 2 and N py ...NO 2 interactions.