Synthesis and Lewis acid properties of (ReO_3F)_∞ and the X-ray Crystal structures of (HF)_2ReO_3F·HF and [N(CH_3)_4]_2-[{ReO_3(μ-F)} _3(μ_3-O)]·CH_3CN

摘要

A high-yield, high-purity synthesis of (ReO_3F)_∞ has been achieved by solvolysis of Re_2O_7 in anhydrous HF (aHF) followed by reaction of the water formed with dissolved F_2 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)_2ReO_3F·HF, was obtained by dissolution of (ReO_3F)_∞ 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, [{ReO_3(μ-F)}_3(μ_3-O)] ~(2-), was obtained as the [N(CH_3)_4]~+ salt by the reaction of stoichiometric amounts of (ReO_3F) _∞ and [N(CH_3)_4]F in CH_3CN solvent at -40 to -20 C. The anion was structurally characterized in CH _3CN 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 [{MO _3(μ-F)}_3(μ_3-O)]2- and [{MO_3(μ-F)}_3(μ_3-F)]- anions (M = Re, Tc) were calculated using density functional theory. The calculated geometries of [{ReO_3(μ-F)}_3(μ_3-O)] ~(2-) and [{TcO_3(μ-F)}_3(μ_3-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(CH_3)_4]_2[{ReO_3(μ-F)} _3(μ_3-O)]·CH_3CN. The X-ray crystal structures of the byproducts, [N(CH_3)_4][ReO_4] and KF·4HF, were also determined in the course of this work.