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 beta- decay of the 191Os-nitrosyl parent complexes were found to undergo secondary chemical reactions to form nitro (NO2-) complexes that were tightly retained on the ion exchanger limiting 191mIr yield to less than 5%.