Technetium V

The structure and chemistry of the square-pyramidal five-coordinate and pseudo-octahedral six-coordinate [TcvO]3+ complexes are dominated by the strong tetragonal distortion induced by the multiply bonded oxo ligand. The d orbital energy levels in C4u symmetry are in 

The TcO IR stretching frequency is sensitive to the presence and nature of the trans ligand. For [TcOX4] (X = Cl, Br, I) this absorption 

The Tc0 04 complexes such as M[Tc0(0CH2CH20)2] (M = Na, NBu4) are relatively weak and hydrolyze in the absence of excess diol (420, 433). The catecholate complex [Tc0(02C6H4)2] is, however, more stable and may be prepared by the addition of a stoichiometric amount of 

The preparation of a variety of [TcO(/3-diketonate)2Cl] complexes has been reported (435). 

The discovery that the neutral, lipophilic 99mTcO complex 36, prepared by the reduction of Tc04 in the presence of the tetradentate propyleneamine oxime ligand, is able to cross the blood-brain barrier in both directions has stimulated much work in this area (19). 

When Tc04 is added to concentrated HCl at room temperature, a yellow solution, thought to contain /ac-LTc OsClsl , is formed and is then converted to an olive-green color on reduction to [Tc OCl4] (35). If the solution is heated, the kinetically controlled product [TcOC ] undergoes further reduction to the yellow thermodynamic product [Tc Cle] . These steps are described by the equations 

TCO4- + 3HC1 [TcOaCljl + 3HC1 + HaO [TcOCbJ- + 3HC1  

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This review covers the coordination chemistry of technetium(V) and-to some extent-rhenium(V). In this survey, the complexes are arranged according to donor-atom sets in the coordination sphere. 

Until the mid 1970s, technetium(V) had been widely ignored and its chemistry misinterpreted. Then, the development of the chemistry of technetium(V) was prompted by the trends and needs of nuclear medicine, which predominantly uses technetium-99m radiopharmaceuticals for a broad range of diagnostics. 

Although technetium(V) complexes have been studied extensively in order to design new radiotracers, investigations of in vivo reactive complexes are still in the formative stages and their potential for mimicking biological substrates is not yet predictable. It is the intention of this review to give an introduction into... 

Foster et al. have developed a method for determining technetium in dissolved nuclear fuel solutions. Tetrapropylammonium pertechnetate is doubly extracted from a basic medium into chloroform and the colored technetium (V) thiocyanate complex is formed in the chloroform phase by the addition of sulfuric acid, potassium thiocyanate and tetrapropylammonium hydroxide. The colored complex absorbs at 513 nm, has a molar extinction coefficient of 46,000 and is stable for several hours. Of more than 50 metals studied, none impairs measurements at ratios less than 100 to 1 mol with respect to technetium. Most anions do not disturb the determination of technetiiun. The standard deviation for a single determination is 0.09 fig over the range of 1 to 20 fig of technetium. 

The potential of the Re -Re couple in LiCl-KCl eutectic at 500 °C is — 0.358 V vs. the standard Pt electrode). 2 2 oxidizes [TcClg] directly to TCO4, but CI2 first produces technetium( v) which is then oxidized to pertechnetate. No oxidation of technetium(iv) by atmospheric oxygen in the presence of sunlight could be achieved. 

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