ETS-NOCV description of σ-hole bonding

Area of Science:

• * Quantum Chemistry
• * Computational Chemistry
• * Chemical Bonding

Background:

• * The σ-hole, a region of positive electrostatic potential, is crucial for understanding non-covalent interactions like halogen bonding.
• * Previous studies have explored σ-holes, but a systematic analysis across various halogenated systems and their interactions is needed.

Purpose of the Study:

• * To systematically describe and quantify the σ-hole in a series of halogen compounds (CF3-X, CH3I, C(CH3)nH3-n-I) and germanium-based systems using ETS-NOCV analysis.
• * To characterize the bonding interactions between these systems and ammonia.
• * To elucidate the factors influencing σ-hole properties and their contribution to bonding.

Main Methods:

• * Application of the Extended Transition State Natural Orbitals for Chemical Valence (ETS-NOCV) analysis.
• * Calculation of deformation density (Δρ1) to identify and quantify σ-holes.
• * Analysis of molecular electrostatic potential (MEP) and orbital interactions.

Main Results:

• * The ETS-NOCV analysis successfully visualized σ-holes as negative-value areas in deformation density.
• * σ-hole size and depth decrease in the order I > Br > Cl > F in CF3-X systems.
• * Substituent effects (fluorine, hydrogen, methyl groups) significantly influence σ-hole characteristics.
• * Bonding with ammonia shows a covalent contribution, with electrostatic energy being a dominant factor.

Conclusions:

• * The study provides a systematic description of the σ-hole phenomenon in diverse chemical systems.
• * The findings highlight the interplay between electronic structure, substituent effects, and non-covalent interactions.
• * Electrostatic interactions play a critical role in stabilizing σ-hole-based bonds.