Potentiometric determination of antimony in metal(II) hexafluoroantimonates(V)

The purpose of this study was to develop an accurate and precise analytical procedure for the determination of the content of antimony in coordination compounds of metal(II) hexafluoroantimonates(V) (M(SbF6)2 compounds, where M=Mg, Ca, Sr or Ba) synthesized in our laboratory. The major problem was to find an appropriate reagent for reductive decomposition of SbF6− to Sb3+ required for the determination of antimony by redox titration. Effective reduction of Sb5+ regardless of the metal M bound to SbF6− species was achieved using metallic aluminium powder in acidic medium. Precipitated Sb0 was quantitatively reoxidized to Sb3+ and determined potentiometrically with KBrO3 or KMnO4. Other metals were determined complexometrically with disodium ethylenediaminetetraacetic acid (EDTA). Highly accurate and reproducible results were obtained in the concentration range 5–25 mg Sb with an RSD smaller than 0.6%. Antimony-fluoro-hydroxo species and fluoride did not interfere with the complexometric determinations of other metals with EDTA. The developed method enabled, for the first time, complete elemental chemical analysis of M(SbF6)2 compounds in the bulk form.