Evaluation of osmium(II)-nitrosyl complexes as a method to increase the yield of the 191Os-191mIr generator

The nitrosyl complexes pentachloronitrosylosmate(II), [OsCl₅(NO)]²⁻, and hydroxytetranitronitrosylosmate(II), [Os(OH)(NO₂)₄(NO)]²⁻, were evaluated as parent species for use on the ¹⁹¹Os-^191mIr generator in an attempt to increase the ^191mIr yield of the generator by providing a direct route to a chemically stable ^191mIr daughter. The uptake of the ¹⁹¹Os-labeled complexes by the inorganic ion-exchangers ZrO₂, SnO₂, PbS, MnO₂ and Al₂O₃ and the organic resin AG MP-1 was measured and prototype generators were prepared using those exchangers that demonstrated greater than 90% uptake of the ¹⁹¹Os-labeled complexes. The ^191mIr(III)-nitrosyl complexes produced subsequent to β⁻ decay of the ¹⁹¹Os-nitrosyl parent complexes were found to undergo secondary chemical reactions to form nitro (NO⁻₂) complexes that were tightly retained on the ion exchanger limiting ^191mIr yield to less than 5%.