Characterization of electronic features of intermolecular interactions involving organic fluorine: Inputs from in situ cryo-crystallization studies on ‒F and ‒CF3 substituted anilines

Pradip Kumar Mondal, Venkatesha R. Hathwar, Deepak Chopra

Index: 10.1016/j.jfluchem.2018.03.016

Full Text: HTML

Abstract

Experimental in situ cryo-crystallization studies performed on aniline derivatives depicts that the molecular packing of these compounds is through the utilization of Csp3/sp2 F F Csp3/sp2, N–H···F–Csp3/sp2, and C–H···F–Csp3/sp2 interactions in the presence of strong N‒H···N hydrogen bonds. This exercise has resulted in the identification of frequently occurring supramolecular synthons involving highly electronegative, less polarizable fluorine atoms in the packing of molecules of –F and –CF3 substituted anilines which are liquids at ambient temperature and pressure in the solid state. These studies demonstrate the nature, energetics and topological properties derived from the electron density in compounds based on F and CF3 substituted anilines (8 anilines) in the solid state. The energetics obtained from PIXELC associated with inclusive intermolecular interactions with significantly high electrostatic contribution is mentionable. The topological analysis brings out the bonding character of these interactions in the crystal packing. It is indeed noteworthy that in situ cryo-crystallization in 2-fluoro-6-(trifluoromethyl)aniline forms unique C(sp2) Fδ+ Fδ- C(sp2) contacts stabilized via electrostatics between the two molecules in the asymmetric unit in addition to N H N H bonds. This feature is also observed in a related isomeric compound, namely 2-fluoro-3-(trifluoromethyl)aniline and establishes the importance of weak fluorine-centered halogen interactions in nucleation and crystal growth.