Aerogen Bonding in NgO2F2 (Ng = Xe, Kr): A Computational Study

Abstract

Aerogen bonding in NgO₂F₂ (Ng = Xe, Kr) was investigated using quantum chemical calculations with O-, N-, and C-donor nucleophiles. Molecular electrostatic potential analysis reveals two σ-hole regions along the extensions of the Ng─O bonds, making NgO₂F₂ closer to XeO₃, but with two binding sites and no distinct π-hole regions as in XeOF₂. All nucleophiles form stable 1:1 and 1:2 adducts, with conventional O- and N-donor lewis bases giving moderate stabilization, while the carbene donors 5-NHC, cAAC, and aNHC bind much more strongly. Structural, atoms-in-molecules (AIM), noncovalent interaction (NCI), natural bond orbital (NBO), and energy decomposition (EDA) analyses show that the stronger carbene adducts arise from shorter Ng…C interactions, larger WBI and BCP values, and enhanced LP(C) → BD*(Ng─O) donation. Minor orientation-dependent LP(donor) → BD*(Ng─F) contributions are also observed in selected adducts. The interactions remain primarily electrostatic, with significant orbital contribution, especially for the carbene adducts. Secondary C─H…O/F interactions, together with smaller but non-negligible back-donation from the lone pairs of Ng, provide additional stabilization to the adducts.