Lewis-Acid Properties of Technetium(VII) Dioxide Trifluoride, TcO₂F₃:  Characterization by ¹⁹F, ¹⁷O, and ⁹⁹Tc NMR Spectroscopy and Raman Spectroscopy, Density Functional Theory Calculations of TcO₂F₃, M⁺TcO₂F₄^- [M = Li, Cs, N(CH₃)₄], and TcO₂F₃·CH₃CN, and X-ray Crystal Structure of Li⁺TcO₂F₄^-

Abstract

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.

Dinuclear oxofluorometallates as a new structural type of d 0 transition metal oxofluoride compound

“…The dinuclear (dimeric) structure of these compounds consists of corner-shared octahedra with a bridging fluorine atom. Fluorine-bridging species [W 2 O 2 F 9 ] À (McFarlane et al, 1971;Buslaev, Kokunov, Bochkareva & Shoustorovich et al, 1972) (Casteel et al, 1998) were found in organic mediums, (CH 3 O) 2 SO, CH 3 CN. The controlled hydrolysis of hexafluorides of molybdenum, tungsten and rhenium also yielded the fluorine-bridged [M 2 O 2 F 9 ] À species (Hoskins et al, 1987).…”

Specific features of the structure of monomeric octahedral d 0-rhenium(VII) oxo complexes

“…The Re-F bonds, which are trans posi tioned to Re=O, are much longer than Re-F cis (Δ = 0.135 Å). The two layer packing of structural units in crystal VII with the shortest distance О···О 3.065 Å, which exceeds the doubled van der Waals radius of oxygen (2.84 Å [22]), is similar to that in the Li[TcO 2 F 4 ] structure [23].…”

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.…”

“…Nevertheless, oligomerization in the case of d 0 transition metal fluoride compounds is common. For example, the fluorine-bridged species [W 2 O 2 F 9 ] À [11,20], [Mo 2 O 2 F 9 ] À [21], [Re 2 O 4 F 7 ] À , [Re 3 O 6 F 10 ] À [9], and possibly [Tc 2 O 4 F 7 ] À[8] have been observed in (CH 3 O) 2 SO and CH 3 CN. In all cases, the fluorine bridges are trans to oxygens in these anions.…”

“…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…”