Publication - Journal Article 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^-