Xenon Trioxide Coordination Complexes of Crown Ethers: (CH2CH2O)4XeO3 and Xe(VI) Hydrates, [(CH2CH2O)6(H2O)XeO3]⋅ H2O and [(CH2CH2O)6(H2O)XeO3]2 ⋅ 2H2O ⋅ HF

Abstract

Following on our report of the first coordination complex between a noble-gas compound and a crown ether, (CH₂CH₂O)₅XeO₃, the reactions and structures of XeO₃ complexes with 12-crown-4 and 18-crown-6 were investigated. The reactions of 12-crown-4 and 18-crown-6 with XeO₃ in dilute aqueous HF solutions yielded (CH₂CH₂O)₄XeO₃ and [(CH₂CH₂O)₆(H₂O)XeO₃]₂ ⋅ 2H₂O ⋅ HF, whereas reactions of 12-crown-4 and 18-crown-6 with moist solid XeO₃ in acetone solutions yielded (CH₂CH₂O)₄XeO₃ and [(CH₂CH₂O)₆(H₂O)XeO₃] ⋅ H₂O. The (CH₂CH₂O)₄XeO₃ and [(CH₂CH₂O)₆(H₂O)XeO₃] ⋅ H₂O complexes are air-stable and shock-insensitive, whereas [(CH₂CH₂O)₆(H₂O)XeO₃]₂ ⋅ 2H₂O ⋅ HF is a treacherous, shock-sensitive detonator. Low-temperature X-ray crystal structures show that XeO₃ is coordinated to the crown ether and H₂O through short Xe- - -O contacts. Mappings of the XeO₃ Hirshfeld surfaces onto 12-crown-4 and 18-crown-6 in (CH₂CH₂O)₄XeO₃ and [(CH₂CH₂O)₆(H₂O)XeO₃] ⋅ H₂O reveal regions of negative electrostatic potential (EP) on the oxygen atoms of the crown ethers and regions of high positive EP on the Xe(VI) atom of XeO₃ that are consistent with σ-hole bonds. The calculated gas-phase geometries, Wiberg bond valences and indices, and empirical bond valences corroborate the descriptions of the shortest Xe- - -$$ contacts as σ-hole bonds. The 12-crown-4, 15-crown-5, and 18-crown-6 complexes of XeO₃ are also compared with the X-ray crystal structures and calculated gas-phase structures of their SbF₃ and SbCl₃ analogues.