Lewis Acid Behavior of ReO₂F₃:  Synthesis of (ReO₂F₃)_∞, ReO₂F₄^-, Re₂O₄F₇^-, Re₃O₆F₁₀^-, and ReO₂F₃(CH₃CN) and Study by NMR Spectroscopy, Raman Spectroscopy, and Density Functional Theory Calculations; and X-ray Structures of [Li][ReO₂F₄], [K][Re₂O₄F₇

Abstract

The reaction of Re2O7 with XeF6 in anhydrous HF provides a convenient route to high-purity ReO2F3. The fluoride acceptor and Lewis base properties of ReO2F3 have been investigated leading to the formation of [M][ReO2F4] [M = Li, Na, Cs, N(CH3)4], [K][Re2O4F7], [K][Re2O4F7]·2ReO2F3, [Cs][Re3O6F10], and ReO2F3(CH3CN). The ReO2F4 -, Re2O4F7 -, and Re3O6F10 - anions and the ReO2F3(CH3CN) adduct have been characterized in the solid state by Raman spectroscopy, and the structures [Li][ReO2F4], [K][Re2O4F7], [K][Re2O4F7]·2ReO2F3, [Cs][Re3O6F10], and ReO3F(CH3CN)2·CH3CN have been determined by X-ray crystallography. [Li][ReO2F4] crystallizes in the tetragonal system, space group P4̄21 m, with a = 4.727(3) Å, c = 8.880(7) Å, V = 198.4(7) Å3, and Z = 2 at 24 °C, R 1 = 0.0378, and wR 2 = 0.1029. [K][Re2O4F7] crystallizes in the monoclinic system, space group P2/n, with a = 5.4990(11) Å, b = 5.1530(10) Å, c = 14.753(3) Å, β = 95.68°, V = 415.99(14) Å3, and Z = 2 at 20 °C, R 1 = 0.0473, and wR 2 = 0.1200. [K][Re2O4F7]·2ReO2F3 crystallizes in the monoclinic system, space group C2, with a = 27.32(2) Å, b = 5.274(5) Å, c = 5.355(3) Å, β = 99.53(4)°, V = 760.9(11) Å3, and Z = 2 at −60 °C, R 1 = 0.0238, and wR 2 = 0.0645. [Cs][Re3O6F10] crystallizes in the triclinic system, space group P1̄, with a = 7.011(1) Å, b = 9.773(2) Å, c = 10.331(2) Å, α = 113.73(1)°, β = 91.05(2)°, γ = 92.42(2)°, V = 647.4(2) Å3, and Z = 2 at −118 °C, R 1 = 0.0522, and wR 2 = 0.0529. ReO3F(CH3CN)·CH3CN crystallizes in the orthorhombic system, space group Pnma, with a = 9.138(3) Å, b = 12.518(5) Å, V = 1045.4(7) Å3, and Z = 4 at −63 °C, R 1 = 0.0198, and wR 2 = 0.0605. The structure of ReO2F4 - consists of a cis-dioxo arrangement of Re−O double bonds in which the Re−F bonds trans to the oxygen atoms are significantly lengthened as a result of the trans influence of the oxygens. The Re2O4F7 - and Re3O6F10 - anions and polymeric ReO2F3 are open chains containing fluorine-bridged ReO2F4 units in which each pair of Re−O bonds are cis to each other and the fluorine bridges are trans to oxygens. The trans influence of the oxygens is manifested by elongated terminal Re−F bonds trans to Re−O bonds as in ReO2F4 - and by the occurrence of both fluorine bridges trans to Re−O bonds. Fluorine-19 NMR spectra show that ReO2F4 -, Re2O4F7 -, and ReO2F3(CH3CN) have cis-dioxo arrangements in CH3CN solution. Density functional theory calculations at the local and nonlocal levels confirm that the cis-dioxo isomers of ReO2F4 - and ReO2F3(CH3CN), where CH3CN is bonded trans to an oxygen, are the energy-minimized structures. The adduct ReO3F(CH3CN)2·CH3CN was obtained by hydrolysis of ReO2F3(CH3CN), and was shown by X-ray crystallography to have a facial arrangement of oxygen atoms on rhenium.

Alkali Metal (Li+–Cs+) Salts with Hexafluorochromate(V), Hexafluorochromate(IV), Pentafluorochromate(IV), and Undecafluorodichromate(IV) Anions

“…It seems that the ACrF 6 compounds were partly reduced by slow penetration of water through the walls of the reaction vessels, as already observed before in some other cases. [71] The crystals were sometimes twinned or of very poor quality. Therefore, all crystallizations were repeated many times.…”

A new synthetic route to rhenium and iodine oxide fluoride anions: The reaction between oxoanions and sulfur tetrafluoride

“…The signals associated with the acetonitrile moieties were assigned based on previous assignments made by Reedijk et al. [16] The signals associated with the ReO 2 F 4 − anion M a n u s c r i p t 7 were assigned based on the previous assignments made by Schrobilgen et al, [6] who used DFT calculations to aid in the assignment of the vibrational modes. (5) 1410(4) 1443 (3) 1416 (2) δ as ( CH 3 ) 1360 (11) with what has previously been reported by Gillespie and Krasznai, [19] Christe et al, [14] M a n u s c r i p t 12 and Boatz et al [15] The Raman spectrum contains signals associated with both the cis-and trans-IO 2 F 4 − anion.…”

“…[2] For example, Bi 2 O 3 , TiO 2, U 3 O 8 , and HgO are fluorinated by SF 4 to BiF 3 (Eq. 1), TiF 4 , UF 6 , and HgF 2 , respectively.…”

Hydrolysis of ammonium oxofluorotungstates: A 19F, 17O and 183W NMR study

“…In accordance with the IR spectrum of [WO 2 F 4 ] 2À , the cis-dioxo isomer was definitively established in solution by this method. The cis-structure of [WO 2 F 4 ] 2À , as well as those of [MoO 2 F 4 ] 2À [6], OsO 2 F 4 [7], [TcO 2 F 4 ] À [8] and [ReO 2 F 4 ] À [9], were characterized by two 19 F NMR resonances (two triplets) of equal intensity associated with an A 2 X 2 spin system. In contrast, the trans-isomer would have all four fluorine ligands equivalent and the 19 F NMR spectrum would consist of a singlet.…”

“…The same 19 F chemical shift trend remains for cis-[WO 2 F 4 ] 2À . An ambiguity exists for the assignment of the F c and F t environments in the cis-OsO 2 F 4 , cis-[TcO 2 F 4 ] À , cis-[ReO 2 F 4 ] À anions which were assigned in reverse order[7][8][9] to those in cis-[WO 2 F 4 ] 2À…”