Intermolecular interactions in crystals of benzene and its mono- and dinitro derivatives: study from the energetic viewpoint

Intermolecular interactions and their role in the crystal packing formation have been studied in benzene, mono-nitrobenzene and all isomers of dinitrobenzene crystals. In both polymorphic structures of benzene, stacking interactions are absent and weak C-H. p hydrogen bonds play the main role in the crystal packing formation. The insertion of nitro groups into the benzene molecule causes the formation of stronger CH center dot center dot center dot O intermolecular hydrogen bonds and stacking interactions instead of weaker C-H. p interactions. The analysis of pairwise interaction energies revealed that the stacking interactions form the primary structural motif in the crystals of nitro-substituted benzenes with the exception of para-dinitrobenzene. The existence of stacking interactions was shown to need not only the special orientation of p-systems but also the polarization of the molecule. It was shown that C-H center dot center dot center dot O hydrogen bonds play the minor role in the crystals of mono-and dinitrobenzenes where these interactions link the primary basic structural motifs. The C-H center dot center dot center dot O hydrogen bonds were shown to be weaker than non-specific interactions in the absence of stacking in the para-dinitrobenzene crystal.