Ditechnetium heptoxide revisited: solid-state, gas-phase, and theoretical studies

Ditechnetium heptoxide was synthesized from the oxidation of TcO2 with O2 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 Tc2O7 crystallizes as a molecular solid in the orthorhombic space group Pbca [a = 7.312(3) A, b = 5.562(2) A, c = 13.707(5) A, and V = 557.5(3) A3]. The Tc2O7 molecule can be described as corner-sharing TcO4 tetrahedron [Tc---Tc = 3.698(1) A and Tc–OBri–Tc = 180.0°]. The EI-MS spectrum of Tc2O7 consists of both mononuclear and dinuclear species. The main dinuclear species in the gas-phase are Tc2O7 (100%) and Tc2O5 (56%), while the main mononuclear species are TcO3 (33.9%) and TcO2 (42.8%). The difference in the relative intensities of the M2O5 (M = Tc, Re) fragments (1.7% for Re) indicates that these group 7 elements exhibit different gas-phase chemistry. The solid-state structure of Tc2O7 was investigated by density functional theory methods. The op...