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

摘要

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 center dot center dot center dot F, F center dot center dot center dot F, C-H center dot center dot center dot pi, F center dot center dot center dot pi, pi center dot center dot center dot pi, N center dot center dot center dot pi, and C-H center dot center dot center dot N interactions). The stabilization energies offered by these different interactions have been estimated by computational methods using Gaussian 09. Interestingly, strong pi center dot center dot center dot pi interaction is found only in six exceptional cases, contradicting the general opinion that the pi center dot center dot center dot pi-stacking synthon is a robust supra-molecular synthon. Thus, other intermolecular interactions such as C-F center dot center dot center dot pi, C-H center dot center dot center dot pi and N center dot center dot center dot pi interactions, which are equally strong in stabilizing crystal packing, are also considered to understand the final supra-molecular arrangements. These results demonstrate that by changing the orientation of -CH=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.