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

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VIII Group 17 (halogen) compounds and complexes
chlorido complexes [1992TAY/COD], thus monotone decrease of the stepwise
formation constants can be expected. Since the data published in [2009GAJ/SIP] are
more complete (the log 10 β q values are reported for five different ionic strengths) the
selection in this review is based on the latter publication.
Figure VIII-24 shows the background and dilution corrected UV spectra of
tin(IV) detected at different chloride concentration in 8 M HClO 4 solution. With
increasing [Cl – ] TOT significant spectral changes were observed, reflecting changes in the
coordination sphere of tin(IV), which provided sufficient information to derive the
formation constants of the tin(IV)-chlorido complexes. The observed spectral changes
+ 2
were best described by the formation of 5 species ( SnCl
3
, SnCl + 2
, SnCl 4 (aq), SnCl −
5
and SnCl − ) at all ionic strengths.
2
6
Figure VIII-24: UV-Spectral changes of tin(IV)-perchlorate solution upon addition of
chloride ion (I c = 8 M H(ClO 4 ,Cl), [Sn(IV)] TOT = 0.221 mM, [Cl – ] TOT = 0 to 0.32 M).
Absorbance
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
190 200 210 220 230 240 250 260
λ / nm
The formation of SnCl +
3
was not detected. Since 119 Sn NMR spectra of
concentrated SnCl 4 solution seem to prove the existence of this species
[1992TAY/COD], the former observation is probably due to the high similarity of the
individual spectrum of SnCl +
3
and SnCl 4 (aq), which prevents their differentiation by the
method used.
The species distribution curves calculated for 8 M HClO 4 background
electrolyte are depicted in Figure VIII-25.
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012