Synthesis and Lewis Acid Properties of (ReO3F)∞ and the X‑ray Crystal Structures of (HF)2ReO3F·HF and [N(CH3)4]2-[{ReO3(μ-F)}3(μ3‑O)]·CH3CN

A high-yield, high-purity synthesis of (ReO3F)∞ has been achieved by solvolysis of Re2O7 in anhydrous HF (aHF) followed by reaction of the water formed with dissolved F2 at room temperature. The improved synthesis has allowed the Lewis acid and fluoride ion acceptor properties of (ReO3F)∞ to be further investigated. The complex, (HF)2ReO3F·HF, was obtained by dissolution of (ReO3F)∞ in aHF at room temperature and was characterized by vibrational spectroscopy and single-crystal X-ray diffraction at -173 °C. The HF molecules are F-coordinated to rhenium, representing the only known example of a HF complex with rhenium. The trirhenium dianion, [{ReO3(μ-F)}3(μ3-O)](2-), was obtained as the [N(CH3)4](+) salt by the reaction of stoichiometric amounts of (ReO3F)∞ and [N(CH3)4]F in CH3CN solvent at -40 to -20 °C. The anion was structurally characterized in CH3CN solution by (19)F NMR spectroscopy and in the solid state by Raman spectroscopy and a single-crystal X-ray structure determination of [N(CH3)4]2[{ReO3(μ-F)}3(μ3-O)]·CH3CN at -173 °C. The structural parameters and vibrational frequencies of the [{MO3(μ-F)}3(μ3-O)](2-) and [{MO3(μ-F)}3(μ3-F)](-) anions (M = Re, Tc) were calculated using density functional theory. The calculated geometries of [{ReO3(μ-F)}3(μ3-O)](2-) and [{TcO3(μ-F)}3(μ3-F)](-), are in very good agreement with their experimental geometries. Calculated vibrational frequencies and Raman intensities have been used to assign the Raman spectra of (HF)2ReO3F·HF and [N(CH3)4]2[{ReO3(μ-F)}3(μ3-O)]·CH3CN. The X-ray crystal structures of the byproducts, [N(CH3)4][ReO4] and KF·4HF, were also determined in the course of this work.