Syntheses and Structures of TcOF5and the Tc2O2F9+Cation and Formation of the TcOF4+Cation in Solution

Abstract

The last member of the series of technetium(VII) oxide fluorides, TcOF5, has been prepared by oxidative fluorination of TcO2F3 with KrF2 in anhydrous HF. The pseudooctahedral (C4v) structure of TcOF5 has been determined by 19F and 99Tc NMR, Raman, and infrared spectroscopies and by single-crystal X-ray diffraction. TcOF5 crystallizes in the orthorhombic crystal system, space group Pna21, with a = 9.235(3) Å, b = 4.939(2) Å, c = 8.502(3) Å, V = 387.7(2) Å3, and Z = 4 at −102 °C, R1 = 0.0256 and wR2 = 0.0730. TcOF5 behaves as a fluoride ion donor toward AsF5 and SbF5 in HF solvent, giving the Tc2O2F9+ cation, which has been characterized as the AsF6- and Sb2F11- salts by Raman spectroscopy and as the [Tc2O2F9][Sb2F11] salt by single-crystal X-ray diffraction. [Tc2O2F9][Sb2F11] crystallizes in the orthorhombic crystal system, space group Pbcm, with a = 6.2925(4) Å, b = 21.205(2) Å, c = 11.7040(8) Å, V = 1561.7(2) Å3, and Z = 8 at −90 °C, R1 = 0.0368 and wR2 = 0.0896. The Tc2O2F9+ cation consists of two fluorine-bridged square pyramidal TcOF4 groups in which the fluorine bridge is trans to the oxygens. Solution 19F and 99Tc NMR spectra of Tc2O2F9+ salts in HF and of TcOF5 dissolved in SbF5 are consistent with the formation of the TcOF4+ cation. Local density functional theory has been used to calculate the geometrical parameters, vibrational frequencies, and 19F and 99Tc NMR parameters of MOF5 (M = Tc, Re, Os) and Tc2O2F9+, which are in good agreement with available experimental values. The results of ab initio calculations and normal coordinate analyses for MOF5 confirm the trans influence of oxygen, which leads to lengthening of the axial fluorine−metal bond length and a correspondingly lower stretching force constant relative to that of the shorter equatorial metal−fluorine bonds.