Ligand exchange and solvolytic reactions of^99mTcBr ²⁻₆ in non-aqueous media

Abstract

Prior work had documented that^99mTcCl ²⁻₆ could undergo ready ligand exchange reaction under non-aqueous condition. We now wish to report the ligand exchange reaction of bromine in^99mTcBr ²⁻₆ in non-aqueous solvents using 8-hydroxyquinoline (oxine) as the displacing ligand. Analysis of the products obtained by paper chromatography, HPLC and electrophoresis suggest that a 1∶2 Tc∶oxine complex appears to be the most stable of the complexes formed, probably^99mTc(oxine)₂ Br₂. However, displacement of bromine by polar solvents (both protic and aprotic) can also occur, both on^99mTcBr ²⁻₆ and in the above complex as a consequence of solvolytic reactions. Other Tc-oxine complexes can also be formed upon ligand exchange, but they appear to be stable only under aprotic, non solvolytic conditions. These studies again document that hexahalotechnetate complexes exhibit ligand exchange reactions under non-aqueous conditions, that they allow the ready synthesis of novel technetium complexes, but that because of their high reactivity the effect of competing reactions must be considered.