CHAPTER 9. Quantitative Analysis of Weak Non-covalent σ-Hole and π-Hole Interactions

Abstract

Weak non-covalent interactions play an essential role in supramolecular chemistry. The recognition of molecules is the outcome of the mutual interaction through various forces that are in operation. In this chapter, we are particularly interested in focusing on σ-hole and π-hole interactions. In generally, the σ-hole is located along the vector of a covalent bond such as X–Y where X = any atom and Y = halogen, chalcogen, pnictogen and tetrel (X–Tr) atoms. The corresponding interactions are termed as halogen (Hlg), chalcogen (Ch), pnictogen (Pn) and tetrel (Tr) bonding interactions. In π-acidic systems like a carbonyl group or a hexafluorobenzene ring, the hole is located perpendicular to the molecular framework. In this chapter, the physical nature of σ-hole and π-hole interactions is described to give an overview of these weak interactions.We have combined theoretical density functional theory calculations and Hirshfeld surfaces to characterize the interaction in a series of selected examples retrieved from the Cambridge Structural Database (CSD). A graphical tool based on Hirshfeld surfaces is used to visualize and to analyze the fidelity of weak intermolecular interactions involving π-hole and σ-hole interactions of molecular crystals. In spite of the non-spherical distribution of the charge density at the σ-hole donor atoms, we show in this chapter the usefulness of Hirshfeld surfaces and associated fingerprint plots of the structures retrieved from CSD to quantify weak σ-hole and π-hole interactions in a novel visual manner.