Technetium III

Potassium heptacyanotechnctate(III)-dihydrate, K4[Tc(CN)7j 2H2O, was synthesized by reaction of (Ml4)2[TcTf,] with KCN in refluxing aqueous methanol under exclusion 

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Tris(dioxime) complexes that are capped with a boryl group BR at only one end of the molecule are also known, e.g., with technetium(III) [227, 228] and rhenium(III) [229]. 

Non-ionic thiourea derivatives have been used as ligands for metal complexes [63,64] as well as anionic thioureas and, in both cases, coordination in metal clusters has also been described [65,66]. Examples of mononuclear complexes of simple alkyl- or aryl-substituted thiourea monoanions, containing N,S-chelating ligands (Scheme 11), have been reported for rhodium(III) [67,68], iridium and many other transition metals, such as chromium(III), technetium(III), rhenium(V), aluminium, ruthenium, osmium, platinum [69] and palladium [70]. Many complexes with N,S-chelating monothioureas were prepared with two triphenylphosphines as substituents. 

The technetium(III) complexes are synthesized by the direct reduction of pertechnetate with an appropriate reductant in the presence of the desired ligand. However, when sodium dithionite is used as a reductant, the oxidation state of the synthesized complex varies from III to V, depending significantly on the nature of the coexisting ligand. 

An interesting investigation of a ligand exchange reaction for Tc(III) complex has been reported in the system of tris(acetylacetonato)technetium(III)... 

These procedures were further extended to tris(acetylacetonato)technetium(III) [24]. In an acetonitrile solution of Tc(acac)3, the absorbances at the characteristic absorption maxima at 348,375,505 and 535 nm decreased with time, while an increase in the absorbance at 272 nm corresponded to an increase of free acetylacetone liberated during the substitution reaction. The final absorption spectra of the reaction mixture exhibited absorption maxima at 271,325 and 387 nm. The first order rate constant k for decomposition was found to be k = (8.86 + 0.08) x 10 4s 1at [H+] = 2.0 M at 30°C. 

Ligand Substitution Reactions of Hexakis(Thiourea)Technetium(III)... 

The reduction of pertechnetate with concentrated hydrochloric acid finally yields the tetravalent state, and no further reduction to the tervalent state takes place. Therefore, the tervalent technetium complex has usually been synthesized by the reduction of pertechnetate with an appropriate reductant in the presence of the desired ligand. Recently, the synthesis of tervalent technetium complexes with a new starting complex, hexakis(thiourea)technetium(III) chloride or chloropentakis(thiourea)technetium(III) chloride, has been developed. Thus, tris(P-diketonato)technetium(III) complexes (P-diketone acetylacetone, benzoyl-acetone, and 2-thenoyltrifluoroacetone) were synthesized by the ligand substitution reaction on refluxing [TcCl(tu)5]Cl2 with the desired P-diketone in methanol [28]. 

Crystals of [Tc(tu)6]Cl3 or [TcCl(tu)5]Cl2 are often employed for the synthesis of technetium(III) complexes. However, since the direct reduction of pertechnetate with excess thiourea in a hydrochloric acid solution yields [Tc(tu)6]3+ in high yield [37], direct use of the aqueous solution of the thiourea complex would be preferable for the synthesis of the technetium(III) complex without isolation of the crystals of the thiourea complex. In fact, technetium could be extracted from the aqueous solution of the Tc-thiourea complex with acetylacetone-benzene solution in two steps [38]. More than 95% extraction of technetium was attained using the following procedure [39] First a pertechnetate solution was added to a 0.5 M thiourea solution in 1 M hydrochloric acid. The solution turned red-orange as the Tc(III)-thiourea complex formed. Next, a benzene solution containing a suitable concentration of acetylacetone was added. After the mixture was shaken for a sufficient time (preliminary extraction), the pH of the aqueous phase was adjusted to 4.3 and the aqueous solution was shaken with a freshly prepared acetylacetonebenzene solution (main extraction). The extraction behavior of the technetium complex is shown in Fig. 6. The chemical species extracted into the organic phase seemed to differ from tris(acetylacetonato)technetium(III). Kinetic analysis of the two step extraction mechanism showed that the formation of 4,6-dimethylpyrimidine-... 

Thiourea complexes of technetium(III) have been shown to be excellent precursors for the synthesis of a large number of Tc and Tc complexes. The [Tc(tu)6] cation is readily formed in a mixture of pertechnetate, tu and 12 M HCl and precipitates as chloride. Due to the different redox potentials of the homologous elements technetium and rhenium, the reducing capacity of HCl is not sufficient to apply the same method for rhenium and tin chloride is added as reducing... 

Dioxazolines, synthesis, 30 271 Dioximes, technetium(III) complexes, 41 33-36 Dioxocyclam, 45 96 Dioxohexakis(trimethylsilylmethyl)-... 

Technetium(III) is one of the more accessible oxidation states and has been shown to complex with a variety of ligands in several coordination geometries. In general, the trivalent state of technetium appears to require the presence of good pi-acceptor ligands such as triphenylphosphine, diarsines, or carbonyl for stabilization. 

Attempts to isolate clathrochelate technetium (III) tris-dioxi-mates via template cross-linking three dioxime molecules with alkylboronic acid have not been successful. Only semiclathrochelate TcNx(HNx)2(BR2)Hal and TcDm(HDm)2(BR2)Hal complexes (where HaF is Cr, Br R is CH3 and A1-C4H9) were prepared [87, 88],... 

A. Organometallic Complexes Halide Complexes and Clusters Complexes with Nitrogen Ligands Phosphine, Arsine, and Related Complexes Complexes with Sulfur Ligands Nitrosyl and Thionitrosyl Complexes Technetium(III)... 

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