Contribution of Nonaxial n → σ* Orbital Interactions in Tetrel Bonding: A Case Study on Si…N Interactions

This study reveals the critical role of nonaxial n → σ* orbital interactions in stabilizing Si···N tetrel bonds. Through computational analysis and comparison with crystal structures, it is demonstrated that nonaxial interactions significantly enhance bond strength and complement conventional axial bonding, offering new insights into the nature of σ-hole interactions.

The formation of a σ-hole interaction is typically associated with a corresponding n → σ* orbital interaction. This study examines the role of these n → σ* interactions in stabilizing Si…N tetrel bonding within various dimeric complexes. While conventional n → σ* orbital overlap along the tetrel bonding axis is observed as expected, the findings highlight the presence and significant contribution of additional nonaxial n → σ* orbital interactions in sp ³-hybridized silicon dimers. Traditional theories of tetrel bonding emphasize linear interactions along the σ-hole axis, characterized by direct head-to-head n → σ* overlaps. However, this study reveals that nonaxially oriented σ* orbitals of the tetrel atom can also substantially interact with electron donors, significantly enhancing the stability of Si…N tetrel bonds. Depending on the substituents in the dimeric complexes, nonaxial n → σ* interactions can contribute notably higher to the stabilization than their axial counterparts.

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