Unraveling the Strength and Nature of Se•••O Chalcogen Bonds: A Comparative Study of SeF2 and SeF4 Interactions with Oxygen-Bearing Lewis Bases

Chalcogen bonds (ChBs) involving selenium have attracted substantial scholarly interest in past years owing to their fundamental roles in various chemical and biological fields. However, the effect of the valency state of the electron-deficient selenium atom on the characteristics of such ChBs remains unexplored. Herein, we comparatively studied the sigma-hole-type Se center dot center dot center dot O ChBs between SeF2/SeF4 and a series of oxygen-bearing Lewis bases, including water, methanol, dimethyl ether, ethylene oxide, formaldehyde, acetaldehyde, acetone, and formic acid, using ab initio computations. The interaction energies of these chalcogen-bonded heterodimers vary from -5.25 to -11.16 kcal/mol. SeF2 participates in a shorter and stronger ChB than SeF4 for all the examined heterodimers. Such Se center dot center dot center dot O ChBs are closed-shell interactions, exhibiting some covalent character for all the examined heterodimers, except for SeF4 center dot center dot center dot water. Most of these chalcogen-bonded heterodimers are predominantly stabilized through orbital interactions between the lone pair of the O atom in Lewis bases and the sigma*(Se-F) antibonding orbitals of Lewis acids. The back-transfer of charge from the lone pair of selenium into the sigma* or pi* antibonding orbitals of Lewis bases is also observed for all systems. Energy decomposition analysis reveals that the electrostatic component significantly stabilizes the targeted heterodimers, while the induction and dispersion contributions cannot be ignored.