Technetium compounds 71-complexes

Using the cascade of 0.59-0.54. VIeV emitted by " Tc, Tc was determined in samples of 1-2 mg of technetium complex compounds by neutron activation analysis. Moderate sample activities were obtained after an irradiation time of 20 s at a neutron flux of about 10 cm "-s Good agreement between expected and found Tc contents was observed. The uncertainty of the mean value could be restrieted to less than 1 % ]26]. 

Technetium complexes with thioethers in the strict sense, i.e., those without other donor groups in the ligand molecule, comprise homoleptic thioether nitridotechnetium(V) complexes [111], cationic mixed thioether/thiolate complexes of Tc(III) [112], and a cationic Tc(I) complex [113]. However, these latter compounds do not properly fall within the scope of Tc(V) compounds and are excluded from review. 

The most convenient route to organometallic technetium complexes is directly from 3, under reaction conditions which allow working in a normal laboratory. There are basically three essential compounds that fulfil these conditions and can be prepared in a one step synthesis starting from 3, and which are convenient precursors for subsequent chemistry due to their reactivity (Scheme 1). 

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]... 

Thus, the investigations performed [58,77] showed that [Tc2(/t-CH3COO)4] [TCO4J2 combines the properties of two classes of technetium complexes those of pertechnetates and those of binuclear carboxylates with multiple M-M bonds. On the other hand, the anionic and cationic fragments of this compound are characterized by a mutual effect which affects their electronic and molecular structures. 

The extraction of technetiiun by different organic solvents is used in numerous separation and concentration procedures. Technetium is extracted as pertechnetate or, in lower oxidation states, as a complex compound. TcO can be extracted by the following main types of reactions ... 

In addition to pertechnetate various complex compounds of lower valent technetium can be extracted (Table 7). 

Pertechnetate can also be reduced by p-thiocresol in acetic acid solution. With an excess of the reducing agent technetium forms a complex compound which readily dissolves in non-polar solvents such as chloroform, toluene or benzene. 

Pertechnetate and molybdate are reduced in acetic acid media by p-thiocresol and form complex compounds. As mentioned above the technetitun compound can be extracted by chloroform. Since the blue molybdenum complex is insoluble in this solvent separation of technetium from molybdenum can be achieved " . 

Cyclopentadienyl (Cp) complexes (see Cyclopentadienyl) are known for almost all the metals of the periodic chart, including technetium. The compounds with transition metals usually possess covalent jt Cp M bonding. The nature of the metal Cp bond is multiple. The <7-bond is formed from the overlap of an empty d orbital of Tc with one of the frUed jt bonding molecular orbital on Cp with good symmetry. Back-donation is usually also present from the filled d orbitals of Tc to one of the empty n molecular orbitals on Cp. These molecules are usually called sandwich compounds (see Sandwich Compound), when there are two Cp ligands bonded to the metal, or half-sandwich complexes (see Half-sandwich Complexes) when only one Cp ligand is present. 

The importance of technetium-99m radiopharmaceuticals stimulated numerous studies related to the basic chemistry of long-lived technetium Tc. A great number of technetium complexes reviewed in the preceding sections has been synthesized and characterized. Exact technetium analyses in these compounds have been needed to confirm their composition. Besides the traditional determinations of Tc by conductometric titrations of pertechnetate or by liquid scintillation counting, neutron activation of Tc has also been... 

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