The reduction of pertechnetate-99 by stannous chloride—II. The stoichiometry of the reaction in aqueous solutions of several phosphorus(V) compounds

Abstract

The reduction of pertechnetate-99 by excess stannous chloride in 1 M sodium phosphate at pH 7 produced a mixed-metal complex of Tc(III), Tc(IV), and Sn(II). This was shown by polarography and spectrophotometry. Coulometry at fixed potential produced a Tc(III) complex which was air-oxidized to a Tc(IV) complex, in agreement with other reports. In 0.2 M sodium pyrophosphate at pH 7, both coulometry at fixed potential and reduction by excess SnCl 2 produced compounds which slowly turned deep blue. From their identical visible absorption spectra, it was tentatively concluded that they were the same, as were their oxidation products (pink), and from the coulometry it was concluded that Tc(III) has been formed. In 1 M potassium pyrophosphate at pH 7, excess SnCl 2 and coulometry produced almost colorless solutions; dilution to 0.2 M pyrophosphate did not cause the blue complex to appear. Qualitatively, it was shown that the pyrophosphate complex was more stable than one formed in a sodium polyphosphate solution. The close resemblance between the spectrum of Tc(III) phosphate and that of Tc(III) pyrophosphate was explained by assuming that the phosphate complex was formed from a hydrogen-bonded dimer of phosphoric acid.