Technetium Carbonyl Complexes in Water

Besides the stability of the CO ligands towards ligand exchange, oxidation stability in aqueous solution is, in particular, remarkable. Cyclovoltametric experiments showed that the oxidation potential must be higher than 1.2 V in water. As described later, the 99mTc compound is moderately air sensitive at high dilution. [Re(OH2)3(CO)3]+ and [ Tc(OH2)3(CO)3]+ are stable when exposed to air. 

BC parallels the behaviour of metallacarboxylic acids which could potentially also serve as in situ CO sources along the same pathway. BC comprises two functions in one anion the reducing function of [BHJ- and CO as a ligand. 

BC is reasonably stable at neutral-to-alkaline pH but decomposes rapidly in acidic media. The reaction of [99mTc04] with BC at pH 11-12 yields quantitatively the organometallic aqua ion [99mTc(OH2)3(CO)3]+. Mechanistically, it is possible that BC acts as a ligand which binds to the technetium centre. Hydride transfer followed or paralleled by reduction occurs concomitantly with CO coordination. The X-ray structure of a model with K+ as the metal is shown in Fig. 1. 

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