Chromium(VI) Oxyfluoride Dianions, [Cr2O4F6]2− and [CrO2F4]2−; Syntheses and Structures of [XeF5]2[Cr2O4F6], [XeF5]2[Cr2O4F6] ⋅ nX (X=HF, n=4; X=XeOF4, n=2), and [XeF5][Xe2F11][CrO2F4]

The fluorobasic character of the strong oxidative fluorinator, XeF₆ , and the oxidative resistance of the [XeF₅ ]⁺ and [Xe₂ F₁₁ ]⁺ cations have been exploited for the syntheses of several novel Cr(VI) dianion salts. The reactions of XeF₆ and CrO₂ F₂ in anhydrous HF and by direct fusion of the reactants in melts have yielded the first dinuclear Cr(VI) oxyfluoro-dianion salts, [XeF₅ ]₂ [Cr₂ O₄ F₆ ], [XeF₅ ]₂ [Cr₂ O₄ F₆ ] ⋅ 4HF, [XeF₅ ]₂ [Cr₂ O₄ F₆ ] ⋅ 2XeOF₄ , and mononuclear Cr(VI) oxyfluoro-dianion salt, [XeF₅ ][Xe₂ F₁₁ ][CrO₂ F₄ ]. The salts were structurally characterized by low-temperature (LT) single-crystal X-ray diffraction (SCXRD) and LT Raman spectroscopy. The [CrO₂ F₄ ]^2- and [Cr₂ O₄ F₆ ]^2- dianions have distorted octahedral cis-dioxo Cr(VI) coordination spheres in which two F-atoms are trans to one another and two F-atoms are trans to O-atoms, where the [Cr₂ O₄ F₆ ]^2- dianion is the fluorine-bridged dimer of the [CrO₂ F₃ ]^- anion. Quantum-chemical calculations were used to obtain the energy-minimized, gas-phase geometries, and the calculated vibrational spectra of the gas-phase dianions and their ion-pairs, which were used to aid in the vibrational frequency assignments of the crystalline salts. NBO and MEPS analyses and SCXRD show these salts are comprised of intimate ion-pairs in which their cations and anions interact through primarily electrostatic Xe- - -F σ-hole bonds.