Hydrothermal Routes to Technetium Cluster Compounds

Transition metals of groups six through nine exhibit unique direct multiple metal-metal bonding cores. Technetium is a group seven transition metal and is the lightest radioelement in the periodic table. Technetium exhibits nine oxidation states (from -I to VII) and an extensive set of mixed oxidation states due to bi- or poly- nuclear complex formation. Technetium has no stable isotopes and thirty four technetium isotopes have been discovered. Two main isotopes are of great importance 99Tc and its metastable nuclear isomer 99mTc. The isotope 99mTc (T1/2 = 6.01 hours, γ = 140.5 keV) is used in diagnostic nuclear medicine while 99Tc (T1/2 = 2.13x105 years, β = 294 keV) is a prominent fission product and is mainly used in fundamental technetium chemistry research due to its long half-life. The isotope 99Tc is a concern in nuclear waste management due to its high production rate, mobility in the environment, long half-life and radiotoxicity. The rapid use of technetium in various diagnostic procedures extended its coordination chemistry but the fundamental chemistry of low valent technetium is not as well explored compared to the surrounding elements Mo, Re, and Ru. Currently over 200 compounds containing the Re2+n (n = 4, 5, 6) cores are known, whereas less than 30 compounds with Tc2+n (n = 4, 5, 6) cores exist. One example of a Tc2+6 core is Tc2(O2CCH3)4Cl2 which has been shown to be a useful starting compound for the synthesis of technetium binary halides. Hydro/solvo-thermal synthesis methods are used to reduce pertechnetate species, Tc(VII), to low-valent stable Tc-Tc dimers by changing the temperature and pressure of the system under constant volume and with different salts and acids. Results of these hydro/solvo-thermal reactions have yielded various new ditechnetium compounds that show interesting structures and properties. This study will focus on the synthesis of molecular metal-metal bonded technetium compounds like Tc2(μ-O2CCH3)4X2, (X = Cl, Br), polymeric metal-metal bonded technetium compounds or chains as [Tc2(μ-X)4(η-Y)]n, (X = carboxylate; Y = carboxylate, I) and technetium cluster chemistry involving iodide as polynuclear species for K[Tc8(μ-I)8I4]I, and Tc5I5(μ-I)4(μ3-I)4. As a result, these studies related to the synthesis of technetium dimers/clusters will permit acquisition of new information on technetium metal-metal bond chemistry and thus extend the fundamental knowledge of this element as well as its potential applications in the nuclear fuel cycle or nuclear medicine