Tuning σ‑Hole Chalcogen···Nitrogen Bonding Between C₂F₄Ch₂ and Nitrogen Bases: Dual Modulation by Chalcogen Atomic Size and Nitrogen Hybridization (Ch = S, Se, Te, Po)

The two moieties are held together primarily through the Ch···N ChBs. These ChBs show substantial bond contraction, with Ch···N distances approximately 12–29% shorter than the sum of the respective van der Waals radii. Topological analysis indicates that although most Ch···N ChBs exhibit noncovalent closed-shell characteristics, Te/Po···N ChBs in complexes with NH₃, NHCH₂, or pyridine display a partially covalent nature.

Notably, the Ch···N ChB strength typically increases in the order Ch = S < Se < Po < Te and follows the nitrogen base sequence: NCH (sp) < NH₃ (sp³) < NHCH₂ (sp²) < pyridine (sp²). Natural bond orbital (NBO) analysis suggests that the predominant orbital interaction associated with the Ch···N ChB involves charge transfer from the nitrogen lone pair into the σ*(C–Ch) antibonding orbitals.

Energy decomposition analysis reveals that electrostatic interactions provide the largest attractive contribution to the stabilization of these chalcogen-bonded complexes. These findings provide critical insights into the tunability of chalcogen bonding interactions by modulating the atomic and electronic structures of the interacting partners.