Comment on “Thermodynamic Data for Sn(IV) Species in Aqueous Solution: Matter of Controversy and Error”

Abstract

May and Filella (J Solution Chem 52:754–761, 2023) concluded that they had verified the data in Gamsjäger et al. (Chemical thermodynamics of tin OECD, Nuclear Energy Agency Data Bank, Leoben, 2012). However, they used exactly the same primary data and not surprisingly came up with essentially the same values. They (1) provided no new data; (2) did not comment on/re-evaluate the existing experimental data (e.g., Sn–Cl complexes) that determine the accuracy of the E⁰ value for the (Sn⁴⁺/Sn²⁺) couple, but instead relied on a calculated value that is precise but of questionable accuracy; (3) disregarded extensive cassiterite (SnO₂(cass)) solubility data that is critical to (a) ascertaining the accuracy of the E⁰ value based on \({\mathrm{Sn}(\mathrm{Cl})}_{y}^{4-\mathrm{y}}\) complexes presented in Gamsjäger et al. (2012) and May and Filella (2023), (b) determining the solubility product of SnO₂(cass), and (c) determining reliable overall K⁰ values for SnO₂(s) solubility reactions involving \({\mathrm{Sn}(\mathrm{OH})}_{n}^{4-n}\) instead of Sn⁴⁺; and (4) in no way help resolve the many orders of magnitude differences in reported K⁰ values for various Sn(IV)–OH system reactions. These issues were extensively addressed in Rai (J Solution Chem.51:1169–1186, 2022) and are briefly discussed herein, and they help to determine that, contrary to May and Filella’s (2023) conclusions, the Sn(IV)–OH system thermodynamic constants presented in Rai (2022) are indeed reliable.