Experimental and computational insights into the nature of weak intermolecular interactions in trifluoromethyl-substituted isomeric crystalline N-methyl-N-phenylbenzamides

The knowledge about the prevalence of weak interactions in terms of the nature and energetics associated with their formation is of significance in organic solids. In the present study, we have systematically explored the existence of different types of intermolecular interactions in ten out of the fifteen newly synthesized trifluoromethyl derivatives of isomeric N-methyl-N-phenylbenzamides. Detailed analyses of all the crystalline solids were performed with quantitative inputs from interaction energy calculations using the PIXEL method. These studies revealed that in the absence of a strong hydrogen bond, the crystal packing is mainly stabilized by a cooperative interplay of weak C-H center dot center dot center dot O-C, C-H center dot center dot center dot pi, and C(sp(2))/(sp(3))-H center dot center dot center dot F-C(sp(3)) hydrogen bonds along with other related interactions, namely, pi center dot center dot center dot pi and C(sp(3))-F center dot center dot center dot F-C(sp(3)). It is of interest to observe the presence of short and directional weak C-H center dot center dot center dot O=C hydrogen bonds in the packing, having a substantial electrostatic (coulombic + polarization) contribution towards the total stabilization energy. The C(sp(3))-F group was recognized in the formation of different molecular motifs in the crystal packing as utilizing different intermolecular interactions. The contribution from electrostatics among the different weak hydrogen bonds was observed in the decreasing order: C-H center dot center dot center dot O=C > C-H center dot center dot center dot F-C(sp(3)) > C-H center dot center dot center dot pi. Furthermore, there was an increase in the electrostatic component with a concomitant decrease in the dispersion component for the shorter and directional hydrogen bonds.