Use of ab initio calculations to provide insights into the strength and nature of interfluorine interactions

Short interfluorine contacts (F-F) are ubiquitous in crystal structures. This article presents a theoretical study of five dimeric complexes formed between fluorine-containing molecules and hydrogen fluorine at the MP2 computational levels. The results derived from ab initio calculations show that in all cases, the intermolecular distances are less than the sum of van der Waals radii. Difluorine bond energies, computed at the MP2/ aug-cc-pVTZ level of theory, span over a range from -0.71 to -3.77 kj/mol, thus indicating that interfluorine interactions are relatively very weak but non-negligible. The electrostatic force contributes dominantly to the stability of the systems under investigation, and as such the dispersion interaction makes energetic contributions to binding. As an NBO analysis suggested, the charge-transfer force plays a minor role in the formation of the complexes. Finally, to gain more insights into the nature of interfluorine interactions, topological analysis of the electron density distribution and properties of bond critical points are determined by means of the quantum theory of atoms in molecules.