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)

Abstract Chalcogen bonds (ChBs), a prominent subclass of σ-hole interactions in which Group 16 elements serve as electrophilic sites, have attracted considerable attention in recent years because of their pivotal roles in diverse chemical and biological systems. However, the combined influence of the chalcogen atomic size and the nitrogen atomic hybridization state on the nature and strength of chalcogen···nitrogen (Ch···N) interactions remains underexplored. Herein, σ-hole-type Ch···N ChBs formed between 2,2,4,4-tetrafluoro-1,3-dichalcogenetanes (C2F4Ch2, Ch = S, Se, Te, Po) and nitrogen bases with distinct hybridization patterns (sp-NCH, sp2-NH═CH2, sp2-pyridine, sp3-NH3) are systematically investigated using quantum chemical calculations. The computed interaction energies vary from −16.8 to −62.5 kJ/mol. 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.