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

Abstract

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.

The Nature of the Technetium Species Formed During the Oxidation of Technetium Dioxide with Oxygen and Water

“…The analyzed sample will therefore consist of a mixture of HTcO 4 , TcO 2 and Tc 2 O 7 , and the EI mass spectrum will logically consist of those species and their fragmentation products. This explains why those three species are the dominant peaks of the mass spectrum of the “red” product, and why there is surprisingly good agreement between this mass spectrum and that of pure Tc 2 O 7 …”

“…The sample for EI‐MS analysis was prepared in a custom‐made glass apparatus fabricated at Argonne National Laboratory. The experimental set‐up used here is similar to the one used previously for the study of Tc 2 O 7 . For introduction of wet O 2 in the system, a bubbler of deionized (DI) water was placed between the O 2 gas bottle and the glass tube.…”

“…Structures were optimized with a convergence criterion of a maximum gradient component of 10 –4 E h /Å and a maximum atomic displacement of 3 × 10 –4 Å. Previously, we demonstrated that PBE‐D3 is an accurate predictor for the structure of Tc 2 O 7 ;, however, pure GGAs are known to produce several spurious TD‐DFT charge transfer states and produce larger errors for the excitation energies of non‐local charge transfer excited states , . The inclusion of exact exchange via a long‐range correction has been shown to remedy this problem, and for that reason the excitation energies are computed here with TD‐DFT using long‐range corrected PBE (LRC‐ωPBE) with ω = 0.3a 0 , …”

Uncovering Multiple Metal–Metal Bonding in a Tetranuclear Fluoride Rhenium Cluster or the Curious Case of {[Ni(H2O)6](NH4)4}[Re4F18]·4H2O

“…The changes between the experimental structure and a relaxed, isolated molecule can be mostly attributed to the natural discrepancies between DFT and experiment, and to crystal‐packing forces. The differences caused by packing forces in a related 3 – center bonding system, Tc 2 O 7 , are much smaller than in Re 4 F 18 owing to the larger degree of covalency about the bridging atom in that molecule.…”

Challenges and Solutions for Handling and Characterizing Alkali-Tc-Oxide Salts

“…Research on Tc, although limited, is important as Tc is being produced daily for the radiopharmaceutical industry, and is a significant component of most nuclear wastes. Within the last few decades there has been a significant increase in research efforts to learn how best to store and dispose of Tc for these purposes [8][9][10][11][12][13][14][15][16]. Coupled with these efforts has been a push for advanced analyses of Tc bearing materials using state-of-the-art equipment [12,[17][18][19][20][21][22][23].…”