Technetium IV , III , and I Complexes

Technetium is stabilized at low oxidation states by suitable ligands such as phosphines, isonitriles, carbon monoxide, and thiourea (Gorski and Koch 1970). Organometallic carbonyl (CO) complexes are interesting precursors for a new class of Tc(I) radiopharmaceuticals (Alberto et al. 2001 Schibli et al. 2000). 

99mrji -methylenediphosphonate (MDP) and polyphosphate complexes were studied as Tc complexes, but only one x-ray structure was obtained with the diphosphonate ligand (Subramanian et al. 1975). Tc-MDP is a polymeric species in which tin is incorporated (Libson et al. 1980) (Fig. 2.1.16). The figure shows primarily the configuration at the central technetium. 

6-dimethylphenylcarbamoylmethyl)iminodiacetic acid (HIDA) and several ether derivatives have been evaluated as ligands for complexation, producing Tc complexes suitable as hepatobiliary agents. Tc-IDA complexes have a negative charge (Loberg and Fields 1978). Two molecules of ligand are coordinated to one Tc(III)-core (Nunn et al. 1983) (Fig. 2.1.17). 

Complexes of the Q series are defined by their structure belonging to the [Tc P2L] complexes, with polydentate Schiff bases stabilized at the +3 oxidation state by a tertiary phosphine ligand (Deutsch et al. 1987). In fact, Tc(V)OC1-l-oxo complexes are easily reduced by a two-electron process to Tc(III). The final Tc(III) compound (Fig. 2.1.18) has an octahedral configuration with the two trans phosphines on the apexes and the tetradentate Schiff base on the equatorial plane (Jurisson et al. 1984). Tc-Q12 has a positive charge, the two hydroxyl groups being deprotonated. The Tc complex has been prepared in two steps, with an intermediate Tc(V)-oxo complex (Abrams et al. 1982). 

These complexes are well modified in the backbone, without decreasing the complex stability. Q12 is the best derivative in the series (Deutsch et al. 1987) however, none of these ligands has been used as a myocardial perfusion agent. 

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