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.
Technetium(VII) dioxide trifluoride, TcO 2 F 3 , behaves as a Lewis acid toward the fluoride ion and acetonitrile forming M + TcO 2 F 4 -[M ) Li, Cs, N(CH 3 ) 4 ] salts and TcO 2 F 3 ‚CH 3 CN. Fluorine-19 NMR spectroscopy established that the TcO 2 F 4anion has a cis-dioxo geometry in CH 3 CN solution. Variable-temperature 19 F NMR studies of TcO 2 F 4and TcO 2 F 3 ‚CH 3 CN in CH 3 CN revealed that the one-bond couplings between 99 Tc and the two fluorine environments exhibit widely different degrees of quadrupolar collapse. The 17 O NMR spectra of 17 O-enriched TcO 2 F 4and TcO 2 F 3 ‚CH 3 CN and the 1 H and 13 C NMR spectra of TcO 2 F 3 ‚CH 3 CN indicated that chemical exchange occurs between TcO 2 F 3 ‚CH 3 CN and CH 3 CN solvent. The TcO 2 F 4anion was characterized by X-ray crystallography as its lithium salt crystallizing in the tetragonal system, space group P4 h2 1 m, with a ) 4.706(1) Å, c ) 8.797(2) Å, V ) 194.8(1) Å 3 , and Z ) 2, at 20 °C. Refinement converged with R ) 0.0339 (R w ) 0.0320). The anion geometry is a distorted octahedron with the two oxygen ligands cis to each other and is closely related to the [TcO 2 F 4 ] units in polymeric TcO 2 F 3 . The Raman spectra of M + TcO 2 F 4 -[M ) Li, Cs, N(CH 3 ) 4 ] and TcO 2 F 3 ‚CH 3 CN were assigned under C 2V and C s point symmetries, respectively. Density functional theory calculations at the local and nonlocal levels predict that monomeric TcO 2 F 3 has a trigonal bipyramidal geometry (C 2V point symmetry) and confirm that the cis-dioxo isomers of TcO 2 F 4and TcO 2 F 3 ‚CH 3 CN (CH 3 CN bonded trans to an oxygen) are the energy-minimized structures. † Dedicated to Professor Neil Bartlett on the occasion of his 65th birthday.
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