Involvement of conformational isomerism in the complexity of the crystal network of 1-(4-nitro­phen­yl)-1H-1,3-benzimidazole derivatives driven by C—H⋯A (A = NO2, Npy and π) and orthogonal Npy⋯NO2 and ONO⋯Csp2 inter­actions

A detailed structural analysis of the benzimidazole nitro­arenes 1-(4-nitro­phen­yl)-1H-1,3-benzimidazole, C13H9N3O2, (I), 1-(4-nitro­phen­yl)-2-phenyl-1H-1,3-benzimidazole, C19H13N3O2, (II), and 2-(3-methyl­phen­yl)-1-(4-nitro­phen­yl)-1H-1,3-benzimidazole, C20H15N3O2, (III), has been performed. They are nonplanar structures whose crystal arrangement is governed by Csp2—H⋯A (A = NO2, Npy 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 Npy; π* = Csp2 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⋯Csp2 and Npy⋯NO2 inter­actions.