Structural and computational understanding of weak interactions in “bridge-flipped” isomeric tetrafluoro-bis-benzylideneanilines

Abstract

A structural investigation of the crystal structures of nine pairs of tetra-fluorinated “bridge-flipped” bis-benzylideneanilines has been conducted. The crystal packing patterns were analyzed in terms of intermolecular interactions involving the fluorine and nitrogen atoms (i.e., C–H⋯F, F⋯F, C–H⋯π, F⋯π, π⋯π, N⋯π, and C–H⋯N interactions). The stabilization energies offered by these different interactions have been estimated by computational methods using Gaussian 09. Interestingly, strong π⋯π interaction is found only in six exceptional cases, contradicting the general opinion that the π⋯π-stacking synthon is a robust supramolecular synthon. Thus, other intermolecular interactions such as C–F⋯π, C–H⋯π and N⋯π interactions, which are equally strong in stabilizing crystal packing, are also considered to understand the final supramolecular arrangements. These results demonstrate that by changing the orientation of –CH[double bond, length as m-dash]N–, one can obtain different supramolecular assemblies through various types of intermolecular interactions. The lattice energy was calculated and decomposed into various components using the semi-classical density sums (SCDS) PIXEL method. A detailed analysis of these interactions based on both experimental and computational methods is provided in the manuscript.