Determination of stannous chloride and stannic bromide speciation in concentrated Cl− and Br− media by cyclic voltammetry

Highlight
- The speciation of Sn(IV)-Br- in concentrated Br- media was determined, and the corresponding stability constants of Sn(IV)-Br- complexation were estimated.
- Electrochemical redox mechanism of Sn(IV)/Sn(II) in Br- media was newly proposed based on our Sn(IV)-Br- speciation results.
- The speciation of Sn(II)-Cl- in concentrated Cl- media was also determined, and we found the evidence of Sn(II)Cl5-, Sn(II)Cl62-, and Sn(II)Cl73-.

The speciation of Sn(IV)-Br− and Sn(II)-Cl− in concentrated Br− and Cl− media were investigated by cyclic voltammetry, which is the continuous study from the previously reported Sn(II)-Br− speciation Park and Chang (2016) . We first determined the speciation of Sn(IV)-Br− in concentrated Br− acidic aqueous solutions with ionic strength of 6. SnBrj4 − j complexes with 1 ≤ j ≤ 5 and their corresponding fractional diagrams were determined based on their estimated stability constants, βjSn(IV) − Br−. In acidic aqueous solutions where the concentration of Br− was less than 2 M, both SnBr3 + and SnBr22 + were estimated to be the main Sn(IV)-Br− species. Meanwhile, as the Br− concentration increased > 2 M, the fraction of SnBr5− was significantly increased and became the main species among Sn(IV)-Br− complexes. For the Sn(II)-Cl− speciation, SnClk2 − k complexes with 1 ≤ k ≤ 7 were determined as the concentration of Cl− increased to 6 M in acidic aqueous solutions. The fractional diagrams of SnClk2 − k complexes were obtained from the estimated βkSn(II) − Cl−. Based on the fractions of Sn(II)-Cl− species, SnCl+ was the main species as the concentration of Cl− was less than 1 M. As the Cl− concentration increased from 1 to 6 M, SnCl75 − became dominant among Sn(II)-Cl− complexes. We tried to determine the speciation of Sn(IV)-Cl− by cyclic voltammetry. However, the determination of Sn(IV)-Cl− speciation was experimentally limited because of the potential inversion of electrochemical reduction between Sn(IV)-Cl−/Sn(II)-Cl− and Sn(II)-Cl−/Sn.

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