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

The last member of the series of technetium(VII) oxide fluorides, TcOF 5, has been prepared by oxidative fluorination of TcO 2 F 3 with KrF 2 in anhydrous HF. The pseudooctahedral ( C 4 v ) structure of TcOF 5 has been determined by 19 F and 99 Tc NMR, Raman, and infrared spectroscopies and by single-crystal X-ray diffraction. TcOF 5 crystallizes in the orthorhombic crystal system, space group Pna 2 1, with a = 9.235(3) Å, b = 4.939(2) Å, c = 8.502(3) Å, V = 387.7(2) Å 3, and Z = 4 at −102 °C, R 1 = 0.0256 and wR 2 = 0.0730. TcOF 5 behaves as a fluoride ion donor toward AsF 5 and SbF 5 in HF solvent, giving the Tc 2 O 2 F 9 + cation, which has been characterized as the AsF 6 - and Sb 2 F 11 - salts by Raman spectroscopy and as the [Tc 2 O 2 F 9 ][Sb 2 F 11 ] salt by single-crystal X-ray diffraction. [Tc 2 O 2 F 9 ][Sb 2 F 11 ] 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) Å 3, and Z = 8 at −90 °C, R 1 = 0.0368 and wR 2 = 0.0896. The Tc 2 O 2 F 9 + cation consists of two fluorine-bridged square pyramidal TcOF 4 groups in which the fluorine bridge is trans to the oxygens. Solution 19 F and 99 Tc NMR spectra of Tc 2 O 2 F 9 + salts in HF and of TcOF 5 dissolved in SbF 5 are consistent with the formation of the TcOF 4 + cation. Local density functional theory has been used to calculate the geometrical parameters, vibrational frequencies, and 19 F and 99 Tc NMR parameters of MOF 5 (M = Tc, Re, Os) and Tc 2 O 2 F 9 +, which are in good agreement with available experimental values. The results of ab initio calculations and normal coordinate analyses for MOF 5 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.