Aqua complexes, technetium

Another class of technetium-based radiopharmaceuticals has emerged on the basis of pioneering work done on the development of an air- and water-stable organometallic aqua complex [99mTc(OH2)3(CO)3]+ 25 obtained from re-... 

Notably, another area of interesting research in metal/water interactions involves studies of the acidity and water exchange properties of organometaUic aqua ions [14]. Of particular current interest are technetium-containing organo-metalhc aqua complexes for appHcations in radiopharmaceutical imaging [15]. 

For organometallic systems, acidity values for a number of metal carbonyl aqua complexes have now been reported. In some cases, these complejKS have enhanced rates for water exchange relative to the hexaaqua ion of the same metal. Ease of water exchange in organometallic aqua ions of technetium is essential toward the generation of " Tc-labeled biomolecules for radiopharmaceutical imaging applications. 

Fig. 21. Comparison of half-lives. [Data from Table VII (equatorial ligand substitution, Table VIII (aqua substitution and related reactions) and Table IX (in vivo reactions of technetium and rhenium radiopharmaceuticals) of the complexes described in Section VII,A. Similar symbols denote similar technetium and rhenium complexes.]...

The large effect of the metal-aqua bond strengths (and thus the p/Co values of the [MX(H20)(CN)4]" complexes) (see Tables III and IV) on the reaction rate is nicely illustrated by the plot of log versus the p/Coi value of [MX(H20)(CN)4]"" (see Fig. 23). The observed LFER also points to a dissociative mechanism. The large deviation for the technetium complex (with interesting consequences for nuclear medicinal applications of Tc complexes) is difficult to explain 174). 

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