Ditechnetium Heptoxide Revisited: Solid-State, Gas-Phase, and Theoretical Studies.

Ditechnetium heptoxide was synthesized from the oxidation of TcO with O at 450 °C and characterized by single-crystal X-ray diffraction, electron-impact mass spectrometry (EI-MS), and theoretical methods. Refinement of the structure at 100 K indicates that TcO crystallizes as a molecular solid in the orthorhombic space group Pbca [a = 7.312(3) Å, b = 5.562(2) Å, c = 13.707(5) Å, and V = 557.5(3) Å]. The TcO molecule can be described as corner-sharing TcO tetrahedron [Tc---Tc = 3.698(1) Å and Tc-O-Tc = 180.0°]. The EI-MS spectrum of TcO consists of both mononuclear and dinuclear species. The main dinuclear species in the gas-phase are TcO (100%) and TcO (56%), while the main mononuclear species are TcO (33.9%) and TcO (42.8%). The difference in the relative intensities of the MO (M = Tc, Re) fragments (1.7% for Re) indicates that these group 7 elements exhibit different gas-phase chemistry. The solid-state structure of TcO was investigated by density functional theory methods. The optimized structure of the TcO molecule is in good agreement with the experimental one. Simulations indicate that the more favorable geometry for the TcO molecule in the gas-phase is bent (Tc-O-Tc = 156.5°), while a linear geometry (Tc-O-Tc = 180.0°) is favored in the solid-state.