Covalent bonding and extreme shielding in xenon-icosagen fluoride cations

Although icosagen cations are known to interact significantly with noble gases, well-defined examples exhibiting strong binding energies indicative of covalent character, particularly for the heavier icosagens, remain scarce. In this work, we explore the stability and bonding of a series of XeMF₂⁺ and Xe₂MF₂⁺ (M = B-Tl) cations, focusing on global-minimum structures featuring Xe-M bonds. Ab initio calculations indicate that these species are thermodynamically viable at 298 and 398 K, with all considered dissociation pathways being endergonic. Bonding analyses reveal strong covalent Xe-icosagen interactions for B, Al, and Ga, while In and Tl exhibit weaker bonding character that suggests more ionic interactions, as supported by the selected complementary analyses. Fluoride ion affinities and relativistic ¹²⁹Xe NMR chemical shifts further support the strong electron-withdrawing nature of the MF₂⁺ cations. Overall, the results suggest that, beyond the previously reported XeBF₂⁺, Xe-icosagen compounds such as XeAlF₂⁺ and XeGaF₂⁺ may also be experimentally accessible.