Contribution of Nonaxial n → σ* Orbital Interactions in Tetrel Bonding: A Case Study on Si…N 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 sp³-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.