Technetium behaviour

Rhenium chemistry will not be discussed explicitly in this contribution. Various excellent reviews on the progress of organometallic rhenium chemistry have been published over recent years. [7] Rhenium is only mentioned when its comparison to new technetium compounds is interesting in the present context and the focus is on significant differences in the behaviour of the two homologs. 

Most of the substitution reactions with the homoleptic Tc(I) isocyanide complexes presented in the preceding section had to be performed at elevated temperatures and were often characterized by low yield. The reason for this behaviour is the exceptionally high kinetic and thermodynamic stability of this class of compounds. From this point of view, 4a are not very convenient or flexible starting materials, although they are prepared directly from 3a in quantitative yield. The exceptionally high kinetic and thermodynamic stability is mirrored by the fact that it was not possible to substitute more than two isocyanides under any conditions. On the other hand, oxidation to seven-coordinated Tc(III) complexes occurs very readily. Technetium compounds of this type, which are not expected to be very inert, could open up a wide variety of new compounds, but this particular field has not been investigated very thoroughly. A more convenient pathway to mixed isocyanide complexes that starts with carbonyl complexes of technetium will be described in Sects. 2.3 and 3.2. 

Compared to 32 (see Sect. 3.2), these compounds have the advantage that they react quantitatively under ambient conditions, in water as well as in polar organic solvents. The behaviour towards the ligands depicted in Scheme 7 proved to be identical for rhenium and technetium. The compounds listed in Scheme 7 have been fully characterized. The heterogenous reaction in THF in the presence of isocyanides yielded quantitatively the neutral complex [TcC1(CN-R)2(CO)3]... 

As expected there is a close resemblance in the chemical behaviour of technetium and rhenium whereas the properties of both elements differ considerably from those of manganese. The electronic configuration of technetium in the ground state is 4d 5s. Technetium is a silver-grey metal which tarnishes slowly in moist air. 

Partition behaviour of americium(III) chelates with cupferron and other bidentate reagents was studied spectrophotometrically between a number of inert solvents and dilute HC104 solutions.98 Of special interest may be the data on their extractability and colours of chloroform extracts, collected in a tabular form for cupferronate derivatives of 58 metals. The pH ranges for the formation of cupferronates of 39 metal ions have been shown graphically in this publication.99 Solvent extraction and polarographic techniques were employed to study the possible adducts between technetium and cupferron.100 Evidence indicates a Tcm cupferronate and possibly a pertechnitate adduct, but no indication of a technetium(IV) complex was obtained. 

Radiopharmaceutical formulations based on "mTc may be divided into two major classes.635 The Class I formulations include what may be described as technetium tagged materials. These may be particles such as cells or colloidal substances, or they may be molecular species such as proteins or other large biological molecules. The essential feature of these agents is that their biodistribution behaviour is determined by the nature of the substrate material. Thus the attachment of a "mTc label should have little or no effect on their biodistribution. However, it cannot necessarily be assumed that this will be the case, especially when relatively low molecular weight substrates are involved. 

Landgren, A. Liljenzin, J.O. Extraction behaviour of technetium and actinides in the aliquat-336/nitric acid system, Solvent Extr. Ion Exch. 17 (1999) 1387-1401. 

The behaviour of technetium in the geosphere is of particular importance in nuclear fuel waste management studies because this man-made element has a long half-life and, under ambient conditions in the laboratory, is not readily sorbed on geologic materials. 

For example, the fission products technetium and promethium are unique, in that they do not have any stable isotopes and do not occur in nature in measureable amounts. While promethium has a number of chemical analogues in the other rare-earth elements, this is not the case for technetium, and it is thus difficult to predict its behaviour in the geosphere. 

Experimental Details and Results. A series of experiments was carried out to study the behaviour of TcO, in various solutions in contact with a number of rocks and minerals, under both oxic and anoxic conditions, to determine the conditions that lead to removal of technetium from solution and the role played by the various minerals in this process. 

Beasley, T.M. and Lorz, H.V (1986) A review of the biological and geochemical behaviour of technetium in the marine environment./. Environ. Radioactivity, 3, 1-22. 

Vandergraaf T. T., Tichnor K. V., and George I. M. (1984) Reactions between technetium in solution and iron-containing minerals under oxic and anoxic conditions. In Geochemical Behaviour of Disposed Radioactive Waste. ACS Symposium Series 246 (eds. G. S. Barney, J. D. Navratil, and W. W. Schultz). American Chemical Society, Washington, DC, pp. 25-44. 

Keith-Roach, M. J., and Roos, P. (2004). Redox-dependent behaviour of technetium-99 entering a permanently stratified anoxic fjord (Framvaren fjord, Norway). Estuar. Coast. Shelf Sci. 60, 151-161. 

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