Anatomy of π-hole bonds: Linear systems

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Supramolecular Chemistry

Background:

• Covalent bonds often feature electron density depletion, creating positively charged regions known as σ-holes.
• These σ-holes are responsible for various noncovalent interactions, including hydrogen bonds and halogen bonds.
• Analogous positive electrostatic potential regions, termed π-holes, exist in other molecular systems.

Purpose of the Study:

• To investigate the nature and characteristics of π-hole bonds, particularly in linear molecules.
• To understand the fundamental elements governing π-hole bond formation, including molecular orbitals and electron density.
• To compare the bonding strength of π-hole bonds in linear systems with those in planar systems.

Main Methods:

• Application of quantum chemical calculations to model and analyze π-hole interactions.
• Examination of electron density distributions and electrostatic potentials to identify and characterize π-holes.
• Analysis of the spatial arrangement of molecular orbitals involved in π-hole bonding.

Main Results:

• Linear molecules exhibit π-holes as a circular belt of positive electrostatic potential around the molecular axis.
• Various types of π-hole bonds were studied, including tetrel, chalcogen, aerogen, triel, and those involving group II elements.
• π-hole bonds formed by linear molecules were generally found to be weaker than comparable bonds in planar systems.

Conclusions:

• π-hole bonds represent a significant class of noncovalent interactions, distinct from σ-hole bonds.
• The electronic and spatial properties of molecular orbitals and electron density dictate π-hole bond characteristics.
• Further research into π-hole bonding in diverse molecular architectures is warranted.