Chromium Oxide Tetrafluoride and Its Reactions with Xenon Hexafluoride; the [XeF5]+ and [Xe2F11]+ Salts of the [Cr(VI)OF5]–, [Cr(IV)F6]2–, [Cr(V)OF5]2–, and [Cr(V)2O2F8]2– Anions

Abstract

<p></p><p>Molten mixtures of XeF<sub>6</sub> and Cr<sup>VI</sup>OF<sub>4</sub> in 1:1 and 1:2 molar ratios undergo reduction to Cr(V) and Cr(IV) by means of F<sub>2</sub> elimination to form [XeF<sub>5</sub>][Xe<sub>2</sub>F<sub>11</sub>][Cr<sup>V</sup>OF<sub>5</sub>]∙2Cr<sup>VI</sup>OF<sub>4</sub> and [XeF<sub>5</sub>]<sub>2</sub>[Cr<sup>IV</sup>F<sub>6</sub>]∙2Cr<sup>VI</sup>OF<sub>4</sub>, respectively, as shown by low-temperature (LT) single-crystal X-ray diffraction (SCXRD). A LT Raman spectroscopic study of an equimolar mixture of solid XeF<sub>6</sub> and CrOF<sub>4</sub> and its melt showed that [Cr<sup>VI</sup>OF<sub>5</sub>]<sup>–</sup> is formed as an intermediate. Reaction of [XeF<sub>5</sub>]<sub>2</sub>[Cr<sup>IV</sup>F<sub>6</sub>]∙2Cr<sup>VI</sup>OF<sub>4</sub> with XeF<sub>6</sub> in a melt gave [Xe<sub>2</sub>F<sub>11</sub>]<sub>2</sub>[Cr<sup>IV</sup>F<sub>6</sub>] and [XeF<sub>5</sub>]<sub>2</sub>[Cr<sup>V</sup><sub>2</sub>O<sub>2</sub>F<sub>8</sub>]. Their LT crystal structures revealed that [XeF<sub>5</sub>]<sup>+</sup> and [Xe<sub>2</sub>F<sub>11</sub>]<sup>+</sup> are coordinated to their respective [CrF<sub>6</sub>]<sup>2−</sup> and [Cr<sub>2</sub>O<sub>2</sub>F<sub>8</sub>]<sup>2−</sup> anions by means of Xe---F–Cr bridges to form infinite chain structures. The reactions of a 1:1 molar ratio of XeF<sub>6</sub> and CrOF<sub>4</sub> in anhydrous hydrogen fluoride (aHF) and in mixed CFCl<sub>3</sub>/aHF solvents yielded [XeF<sub>5</sub>]<sub>2</sub>[Cr<sup>V</sup><sub>2</sub>O<sub>2</sub>F<sub>8</sub>]∙2HF and a mixture of [XeF<sub>5</sub>]<sub>2</sub>[Cr<sup>V</sup><sub>2</sub>O<sub>2</sub>F<sub>8</sub>]∙2HF and [XeF<sub>5</sub>]<sub>2</sub>[Cr<sup>V</sup><sub>2</sub>O<sub>2</sub>F<sub>8</sub>]∙2XeOF<sub>4</sub>, respectively. The SCXRD structures of the latter and aforementioned salts provide the first X-ray structures of [CrOF<sub>5</sub>]<sup>2–</sup> and [Cr<sub>2</sub>O<sub>2</sub>F<sub>8</sub>]<sup>2–</sup>. The [XeF<sub>5</sub>]<sub>2</sub>[Cr<sup>V</sup><sub>2</sub>O<sub>2</sub>F<sub>8</sub>]∙2XeOF<sub>4</sub> and [XeF<sub>5</sub>][Xe<sub>2</sub>F<sub>11</sub>][Cr<sup>V</sup>OF<sub>5</sub>]∙2Cr<sup>VI</sup>OF<sub>4</sub> salts were also characterized by LT Raman spectroscopy. Quantum-chemical calculations were carried out to obtain the energy-minimized, gas-phase geometries and vibrational frequencies for [Cr<sup>VI</sup>OF<sub>5</sub>]<sup>–</sup>, [XeF<sub>5</sub>]<sub>2</sub>[Cr<sup>V</sup><sub>2</sub>O<sub>2</sub>F<sub>8</sub>]∙2XeOF<sub>4</sub>, [Cr<sup>V</sup><sub>2</sub>O<sub>2</sub>F<sub>8</sub>]<sup>2–</sup>, [XeF<sub>5</sub>][Xe<sub>2</sub>F<sub>11</sub>][Cr<sup>V</sup>OF<sub>5</sub>]∙2Cr<sup>VI</sup>OF<sub>4</sub>, [Cr<sup>V</sup>OF<sub>5</sub>]<sup>2–</sup>, and to aid in the assignments of their vibrational frequencies.</p><br><p></p>