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], [K][Re₂O₄F₇]·2ReO₂F₃, [Cs][Re₃O₆F₁₀], and ReO₃F(CH₃CN)₂·CH₃CN

The reaction of Re 2 O 7 with XeF 6 in anhydrous HF provides a convenient route to high-purity ReO 2 F 3 . The fluoride acceptor and Lewis base properties of ReO 2 F 3 have been investigated leading to the formation of [M][ReO 2 F 4 ] [M = Li, Na, Cs, N(CH 3 ) 4 ], [K][Re 2 O 4 F 7 ], [K][Re 2 O 4 F 7 ]·2ReO 2 F 3, [Cs][Re 3 O 6 F 10 ], and ReO 2 F 3 (CH 3 CN). The ReO 2 F 4 -, Re 2 O 4 F 7 -, and Re 3 O 6 F 10 - anions and the ReO 2 F 3 (CH 3 CN) adduct have been characterized in the solid state by Raman spectroscopy, and the structures [Li][ReO 2 F 4 ], [K][Re 2 O 4 F 7 ], [K][Re 2 O 4 F 7 ]·2ReO 2 F 3, [Cs][Re 3 O 6 F 10 ], and ReO 3 F(CH 3 CN) 2 ·CH 3 CN have been determined by X-ray crystallography. [Li][ReO 2 F 4 ] crystallizes in the tetragonal system, space group P 4̄2 1 m, with a = 4.727(3) Å, c = 8.880(7) Å, V = 198.4(7) Å 3, and Z = 2 at 24 °C, R 1 = 0.0378, and w R 2 = 0.1029. [K][Re 2 O 4 F 7 ] crystallizes in the monoclinic system, space group P 2/ n, with a = 5.4990(11) Å, b = 5.1530(10) Å, c = 14.753(3) Å, β = 95.68°, V = 415.99(14) Å 3, and Z = 2 at 20 °C, R 1 = 0.0473, and w R 2 = 0.1200. [K][Re 2 O 4 F 7 ]·2ReO 2 F 3 crystallizes in the monoclinic system, space group C 2, with a = 27.32(2) Å, b = 5.274(5) Å, c = 5.355(3) Å, β = 99.53(4)°, V = 760.9(11) Å 3, and Z = 2 at −60 °C, R 1 = 0.0238, and w R 2 = 0.0645. [Cs][Re 3 O 6 F 10 ] crystallizes in the triclinic system, space group P 1̄, 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) Å 3, and Z = 2 at −118 °C, R 1 = 0.0522, and w R 2 = 0.0529. ReO 3 F(CH 3 CN)·CH 3 CN crystallizes in the orthorhombic system, space group Pnma, with a = 9.138(3) Å, b = 12.518(5) Å, V = 1045.4(7) Å 3, and Z = 4 at −63 °C, R 1 = 0.0198, and w R 2 = 0.0605. The structure of ReO 2 F 4 - 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 Re 2 O 4 F 7 - and Re 3 O 6 F 10 - anions and polymeric ReO 2 F 3 are open chains containing fluorine-bridged ReO 2 F 4 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 ReO 2 F 4 - and by the occurrence of both fluorine bridges trans to Re−O bonds. Fluorine-19 NMR spectra show that ReO 2 F 4 -, Re 2 O 4 F 7 -, and ReO 2 F 3 (CH 3 CN) have cis -dioxo arrangements in CH 3 CN solution. Density functional theory calculations at the local and nonlocal levels confirm that the cis- dioxo isomers of ReO 2 F 4 - and ReO 2 F 3 (CH 3 CN), where CH 3 CN is bonded trans to an oxygen, are the energy-minimized structures. The adduct ReO 3 F(CH 3 CN) 2 ·CH 3 CN was obtained by hydrolysis of ReO 2 F 3 (CH 3 CN), and was shown by X-ray crystallography to have a facial arrangement of oxygen atoms on rhenium.