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]
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AbstractThe fluorobasic character of the strong oxidative fluorinator, XeF6, and the oxidative resistance of the [XeF5]+ and [Xe2F11]+ cations have been exploited for the syntheses of several novel Cr(VI) dianion salts. The reactions of XeF6 and CrO2F2 in anhydrous HF and by direct fusion of the reactants in melts have yielded the first dinuclear Cr(VI) oxyfluoro‐dianion salts, [XeF5]2[Cr2O4F6], [XeF5]2[Cr2O4F6] ⋅ 4HF, [XeF5]2[Cr2O4F6] ⋅ 2XeOF4, and mononuclear Cr(VI) oxyfluoro‐dianion salt, [XeF5][Xe2F11][CrO2F4]. The salts were structurally characterized by low‐temperature (LT) single‐crystal X‐ray diffraction (SCXRD) and LT Raman spectroscopy. The [CrO2F4]2− and [Cr2O4F6]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 [Cr2O4F6]2− dianion is the fluorine‐bridged dimer of the [CrO2F3]− 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.
