Chemical Thermodynamics of Tin - Volume 12 - OECD Nuclear ...

VIII.3 Aqueous halide complexes
191
Table VIII-11 (continued)
Method Ionic media t/°C log10
Sn 2+ + 6 Br –
4
SnBr −
6
Reported Recalculated (a) Accepted (b)
β
q
Reference
Ise-Sn 8.0 M NaClO 4 25 2.28 ± 0.13 [1969FED/BOL]
(a) Re-evaluated values, see Appendix A.
(b) Accepted values corrected to molal scale. The accepted values reported in Appendix A are expressed on
the molar or molal scales, depending on which units were used originally by the authors.
(c) Corrected to NaClO 4 medium.
(d) Mössbauer spectroscopy.
(e) Equilibrated at room temperature, then measured in a fast-frozen solution.
VIII.3.3.2 Aqueous Sn(IV) bromides
The complex formation processes in the aqueous tin(IV)-bromide system have been
investigated by 119 Sn NMR spectroscopy [1992TAY/COD]. Since the speciation
suggested by the authors does not involve partially hydrolised bromido complexes (see
also Section VIII.3), reliable thermodynamic data cannot be extracted from
[1992TAY/COD].
VIII.3.4 Aqueous iodide complexes
VIII.3.4.1 Aqueous Sn(II) iodides
Formation constants of Sn(II) iodide complexes according to the reaction
Sn + I SnI
(VIII.14)
2+ 2 q
q −
−
q
have been reported only in [1976SAM/LYA] and [1968HAI/JOH]. The constants
reported in [1976SAM/LYA] were not considered in this review (see Appendix A).
Based on their solubility measurements made in 4 M NaClO 4 solution, Haight and
Johansson [1968HAI/JOH] suggested the formation of six iodido complexes with q = 1,
2, 3, 4, 6 and 8. The re-evaluation of the experimental data indicated that four species
2 q
( SnI
− q
, q = 1, 2, 3, 4) are sufficient to describe the experimental data up to [I – ] tot =
0.6 M (15% replacement of the background electrolyte). The reported and recalculated
constants are listed in Table VIII-12. It should be noted, that the consideration of at least
3
one additional complex (e.g. SnI − 5
) is necessary to fit the solubility data at [I – ] tot >
0.6 M. However, the correct re-evaluation of the experimental data for [I – ] tot > 0.6 M is
hindered by the probably important medium effect, caused by the replacement of the
background electrolyte (NaClO 4 ) by NaI. Therefore further studies are required to
establish the composition and stability of the formed complexes at higher iodide
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012