[en] The long half-life of ⁹⁹Tc and difficulty in retarding Tc migration in the biosphere make fission product Tc a prime candidate for transmutation. However, transmutation of ⁹⁹Tc via neutron irradiation generates stable Ru isotopes whose neutron absorption cross-sections are significant. A cost-effective means of separating Tc and Ru is therefore likely to be required. Technetium hexafluoride is an appreciably volatile compound and may serve as the basis for such a separation. The authors are investigating the chemistry and photochemistry of TcF₆ with an actinide fluoride to establish a link between literature reactivity trends across the 4d and 5f series of transition metal hexafluorides

[en] Fluorine chemistry has received considerable interest during recent years due to its significant role in the life sciences, especially for drug development. Despite the great nuclear medicinal importance of the radioactive metal technetium in radiopharmaceuticals, its coordination chemistry with the fluorido ligand is by far less explored than that of other ligands. Up to now, only a few technetium fluorides are known. This thesis contains the synthesis, spectroscopic and structural characterization of novel technetium fluorides in the oxidation states ''+1'', ''+2'', ''+4'' and ''+6''. In the oxidation state ''+6'', the fluoridotechnetates were synthesized either from nitridotechnetic(VI) acid or from pertechnetate by using reducing agent and have been isolated as cesium or tetraethylammonium salts. The compounds were characterized spectroscopically and structurally. In the intermediate oxidation state ''+4'', hexafluoridotechnetate(IV) was known for long time and studied spectroscopically. This thesis reports novel and improved syntheses and solved the critical issues of early publications such as the color, some spectroscopic properties and the structure of this key compound. Single crystal analyses of alkali metal, ammonium and tetramethylammonium salts of hexafluoridotechnetate(IV) are presented. In aqueous alkaline solutions, the ammonium salt of hexafluoridotechnetate(IV) undergoes hydrolysis and forms an oxido-bridged dimeric complex. It is the first step hydrolysis product of hexafluoridotechnetate(IV) and was characterized by spectroscopic and crystallographic methods. Low-valent technetium fluorides with the metal in the oxidation states of ''+2'' or ''+1'' are almost unknown. A detailed description of the synthesis and characterization of pentafluoridonitrosyltechnetate(II) is presented. The complex was isolated as alkali metal salts, and spectroscopic as well as structural features of the complexes are presented. Different salts of the trans-tetraamminefluoridonitrosyltechnetium(I) cation were prepared via a facile route and were characterized by spectroscopic and crystallographic methods. Ligand exchange reactions of the nitrosyltechnetium complexes are presented.

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[en] The authors study the sup(95m)Tc decay in a K₂sup(99(95m))TcF₆ solid matrix and in solutions and compare the results with those obtained on K₂sup(99(95m))TcCl₆. (Auth.)

[en] The heat capacity of solid and liquid technetium hexafluoride has been measured between 2.3 and 350 K. The standard entropy, S⁰, the enthalpy increment, (H⁰-H⁰₀), and the Gibbs energy function, (G⁰-H⁰₀)/T, have been calculated. At T=298.15 K, the thermodynamic functions have the following values: C⁰/sub p/=157.84 J K^-1xmol^-1, S⁰=253.52 +- 0.25 J K^-1xmol^-1, (H⁰-H⁰₀) =38331 +- 38 J mol^-1, and (G⁰-H⁰₀)/T=-124.95 +- 0.12 J K^-1xmol^-1. TcF₆ has a solid--solid transition at 268.335 K associated with an enthalpy change ΔH⁰/sub tr/=8024.9 +- 5.0 J mol^-1. It melts at 311.14 +- 0.05 K and has an enthalpy of fusion of ΔH⁰/sub f/=4618.86 +- 1.60 J mol^-1. TcF₆ has a lambda-shaped anomaly in the heat capacity with a peak at 3.12 K, probably caused by a transition to a ferromagnetic state. A similar lambda-shaped transition was observed for rhenium hexafluoride at 1.30 +- 0.05 K. The magnetic entropy of TcF₆ is estimated to be 5.823 J K^-1xmol^-1. The third law value for the standard entropy of TcF₆ vapor at 320 K was calculated to be S⁰ (TcF₆, g) =371.278 +- 0.750 J K^-1xmol^-1. Molecular data for TcF₆ lead to a lower value of S⁰ (TcF₆, g, 320 K) = 367.53 J K^-1xmol^-1. The entropy from molecular data can be made to agree with the calorimetric value if the frequency for the inactive vibrational mode ν₆ is lowered to 131 cm^-1 from the reported value of 145 cm^-1. The average energy of the β decay of ⁹⁹Tc was evaluated from the radioactive self-heating of the sample and was found to be 97.2 +- 1.2 keV. This number exceeds the literature value but agrees with a more recent integration of the β spectrum

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[en] Technetium-99 distributions in form of its TcO₃F compounds in the system of liquid-vapour of uranium hexafluoride at the temperature of 93 deg C is studied. It is shown that for the technetium-99 content ratio of 60-200 ng of uranium the distribution coefficient of TcO₃F K (vapour phase-liquid phase ratio of technetium content) constitutes by the results of 46 experiments 0.437±0.034. The distribution coefficient, obtained on the basis of experimental data, exceeds by 1.8 times the value. 3 refs., 3 figs

[en] Critical parameters of molecular fluorides of halogen fluorides CIF, CIF₃, BrF, BrF₃ and TcF₆ on the basis of thermodynamic similarity theory were estimated, the results are presented. The critical parameters (T_k, V_k P_k) were estimated with an error not exceeding 3 rel. %. Analysis based on ψ-factor suggests that TcF₆ is referred to weakly-polar compounds

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[en] The fundamental radiochemical properties of technetium are reviewed as is its role in spent fuel reprocessing. The basic properties are also shown of technetium hexafluoride resulting from oxide fuel fluorination. Sorption-desorption and distillation techniques are described for the separation of TcF₆ and other fluorides and oxyfluorides of fission products from UF₆ and PuF₆. Industrial equipment is also described for fast reactor spent fuel reprocessing where technetium is separated by the fluoride method. The equipment handles 1 ton of spent fuel a day with a resulting decontamination factor of 10⁶ to 10⁷. The composition is shown of fission product contaminants forming volatile fluorides. Technetium hexafluoride may also be separated from UF₆ by means of contact with a nickel mesh at 400 to 500 degC. In the fluoride separation of technetium from UF₆, sorption on NaF and MgF₂ adsorbents was used. The establishment of the most suitable selective sorption conditions and the achievement of reproducible behaviour of TcF₆ in the MgF₂ sorption bed will allow technetium separation and its application in other fields. (J.P.)