Technetium II

Technetium(II) complexes are paramagnetic with the d5 low-spin configuration. A characteristic feature is the considerable number of mixed-valence halide clusters containing Tc in oxidation states of +1.5 to + 3. This area has been reviewed (42). For convenience, all complexes, except those of [Tc2]6+, are treated together here. EPR spectroscopy is particularly useful in both the detection of species in this oxidation state and the study of exchange reactions in solution. The nuclear spin of Tc (1 = f) results in spectra of 10 lines with superimposed hyperfine splitting. The d5 low-spin system is treated as a d1 system in the hole formalism (40). 

Although carbonyl and cyclopentadienyl complexes are well known for Tc(I) and Tc(III), none appear to have been reported for Tc(II). This may be ascribed to the tendency to follow the 18-electron rule, which, due to the odd number of electrons, would require dimer formation for compliance. Similarly, no Tc(II) cyano or isonitrile complexes appear to have been isolated. 

The only monomeric complex is the tetrahedral [TcBrJ2-, identified crystallographically in the product (11) of the remarkable reaction 

The mechanism of formation of 11 is unknown. The Br-Tc-Br bond angles in (TcBrJ2 are approximately tetrahedral, in the range 106.1-112.1°, and the Tc-Br bond distances of 2.388-2.417 A are very short (146). 

Also isolated from the acetic acid reaction is K[Tc2(OAc)4C12], the structure of which shows a distinctly longer Tc-Tc bond distance of 2.1260(5) A, with two axial chlorides at 2.589(1) A 167c). The effective magnetic moment for the three acetate dimers is 1.78 0.05 BM and the EPR spectra are consistent with the unpaired electron equally shared by the two Tc centers in the 5 (blu) antibonding molecular orbital (168,169). 

the metal cation may be partially replaced by HgO, as in the structurally characterized K eK 3 j.(H30),.[Tc2Clg]3-nH20 (157). The [Tc2Clg] anion possesses virtual symmetry with the square-pyramidal end groups in the eclipsed conformation (Fig. 3). The short Tc-Tc distances of 2.117(2) for the (154) and 2.1185(5) A for the pyH salt 

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The chemistry of technetium(II) and rhenium(II) is meagre and mainly confined to arsine and phosphine complexes. The best known of these are [MCl2(diars)2], obtained by reduction with hypophosphite and Sn respectively from the corresponding Tc and Re complexes, and in which the low oxidation state is presumably stabilized by n donation to the ligands. This oxidation state, however, is really best typified by manganese for which it is the most thoroughly studied and, in aqueous solution, by far the most... 

Boyd Chemistry of Technetium. II. Preparation of Technetium metal. J. Amer. chem. Soc. 74, 1852 (1952). 

Isomer shift data, Fe,S4 clusters, 38 20, 50 Isomorphic substitution, 39 179, 186 p-Isonicotinamide complexes, osmium, 37 307 p-lsonicotinamidepoly(proline) complexes, osmium, 37 307 Isonitrile complexes osmium, 37 245 technetium(I), 41 13-14 technetium(II), 41 31 technetium(IIl), 41 45 Isopolymolybdates, 19 239ff 19 265-280 crystallization from aqueous solution, 19 265-269... 

Dinitrogen, Phosphine, Phosphite, and Related Complexes Complexes with Nitrogen Ligands Nitrosyl and Thionitrosyl Complexes Technetium(II)... 

Despite its limited crystal field stabilization, the d complex bis(4-chloroben-zenethiolato)bis(l,2-bis dimethylphosphino ethane)technetium(II), (20), undergoes relatively slow trans to cis isomerization, with a rate constant of 1.6 x s in dichloromethane at ambient temperature. The low-spin d complex [Tc(acac)3] shows a similar reactivity with respect to exchange with " C-labeled acac to [Cr(acac)3]. Activation parameters for the technetium complex are AFT = 119 kJ mol" and A5 = -27 J mol" in acetylacetone. ... 

Most technetium complexes are redox-active and, because of their low-spin electronic configurations, electron transfer to and from technetium complexes is generally facile [8,9]. Technetium(II) is a particularly accessible oxidation state since it can be readily generated by the oxidation of stable Tc(I) complexes or by the reduction of stable Tc(III) complexes. In vivo reduction of Tc(IU) cations to their neutral Tc(II) counterparts has proven to be an important factor in determining the biological distributions of these cations [10,11]. 

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