Expansion of the sigma-hole concept

Area of Science:

• * Computational Chemistry
• * Supramolecular Chemistry
• * Chemical Bonding Theory

Background:

• * Sigma-holes are electron-deficient regions on atoms involved in covalent bonds, leading to attractive noncovalent interactions.
• * Previously observed for Groups V-VII, sigma-hole bonding is highly directional and influenced by atomic properties and molecular substituents.
• * The positive character of sigma-holes generally increases with heavier atoms and electron-withdrawing groups.

Purpose of the Study:

• * To computationally investigate the occurrence of significant sigma-holes in Group IV atoms.
• * To explore the implications of these findings for the general understanding of sigma-hole origins.
• * To expand the concept of sigma-hole bonding to include new chemical environments.

Main Methods:

• * Computational chemistry methods were employed to analyze electron distribution and electrostatic potentials.
• * Focus on molecules containing Group IV elements, alongside analogous structures from Groups V and VI.
• * Analysis of orbital contributions and bonding characteristics.

Main Results:

• * Significantly positive sigma-holes were computationally demonstrated for atoms in Group IV.
• * These positive sigma-holes facilitate noncovalent interactions similar to those observed in Groups V-VII.
• * The study identified analogous sigma-hole phenomena in molecules like (H3C)2SO, (H3C)2SO2, and Cl3PO.

Conclusions:

• * The interpretation of sigma-hole origins needs expansion to include Group IV elements.
• * A sizeable s-orbital contribution to the bonding orbital is permissible, alongside p-character.
• * Doubly occupied bonding orbitals forming coordinate covalent bonds can also give rise to sigma-holes.