Halogen, Chalcogen, and Pnicogen Bonding Involving Hypervalent Atoms

Area of Science:

• * Computational chemistry
• * Noncovalent interactions
• * Supramolecular chemistry

Background:

• * Hypervalent molecules present unique challenges for noncovalent bond formation due to additional substituents.
• * Understanding these interactions is crucial for predicting molecular behavior and designing new materials.
• * Previous studies have focused on traditional bonding, leaving hypervalent interactions less explored.

Purpose of the Study:

• * To investigate halogen, chalcogen, and pnicogen bonding in hypervalent molecules.
• * To quantify interaction energies and analyze structural rearrangements.
• * To explore the influence of substituents and lone pairs on σ-hole characteristics.

Main Methods:

• * Computational modeling of various hypervalent molecular systems (XF5, YF4, YF6, ZF5) with ammonia as a base.
• * Calculation of interaction energies to quantify bond strengths.
• * Analysis of molecular geometry changes from monomer to complex.

Main Results:

• * Pnicogen bonds (ZF5) are particularly strong (up to 50 kcal/mol) with significant structural rearrangement.
• * Hypervalent chalcogen bonds (YF4) are also strong and increase with heavier central atoms.
• * Halogen bonds (XF5) are weaker (~9 kcal/mol) and sensitive to the central atom, while YF6 interactions are minimal.
• * Substitution in SeF6 with hydrogen introduces chalcogen bonds and H-bonds, with SeF3H3⋅⋅⋅NH3 showing the strongest chalcogen bond (7 kcal/mol).

Conclusions:

• * Hypervalent bonding, including pnicogen and chalcogen bonds, can be strong and significantly influenced by molecular structure.
• * The strength and nature of these bonds depend on the central atom, substituents, and lone pair availability.
• * Understanding σ-hole modulation by substituents is key to predicting and controlling hypervalent noncovalent interactions.