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

A Discussion of selected references
395
4−n−1
SnCl
n 1(H2O)
+ H 4−n
+ 6−n− 1 2O(l) SnCl
n(H2O)
+ 6− n
Cl– (n + 1 = 1 – 6)
i.e. even in solution (i) no hydroxido complexes were considered (or were treated
equivalent with the aqua complexes). The authors detected magnetisation exchanges
4−n
between the successively formed SnCl
n(H2O)
6− n
(n = 1 – 6) species, and reported
equilibrium constants for the above reactions (in fact they are dissociation constants).
Since the formation of mixed hydroxido complexes was neglected, these constants are
not reliable.
[1990BEA/MEN]
The behaviour of Sn(II) and Sn(IV) was studied by polarography in H 2 O-HF mixtures
(w HF = 2 to 100%, [Sn 2+ ] tot = 0.001 M). At low mass fraction of HF (w HF = 0.1 to 2.0%)
the species SnF −
3
is present in the solution. With increasing mass fraction of HF
decreasing coordination number of tin(II) was detected. At w HF = 2 to 45% and 45 to
55% the complexes SnF 2 (aq) and SnF + are the predominant species, respectively.
Above w HF = 55% the coordination of HF −
2
is suggested by the authors. In presence of
2
Sn(IV) the formation of SnF − 6
, SnF − 5
and SnF +
3
was reported with increasing mass
fraction of HF. The reported complex formation processes in concentrated hydrogenfluoride
are fundamentally different from those in more dilute aqueous solutions,
therefore the formation constants given in [1990BEA/MEN] were not considered any
further.
[1990KOK/RAK]
Equilibria in Sn(II) salt (sulphate, chloride, perchlorate, fluoride) and in KSnF 3 ,
NH 4 SnF 3 , or NH 4 Sn 2 F 5 solutions was studied as a function of HClO 4 or H 2 SO 4
concentration by 119 Sn NMR. The NMR chemical shift as acid is added is explained.
Regions of existence of Sn(II) chlorido and fluorido complexes are established. A
scheme is proposed for hydrolysis and complexation processes in these solutions.
[1991DJO/ZMB]
In order to interpret the interaction between tin(II) and hippuric acid, the authors
investigated the hydrolysis of tin(II) ion by pH-metric titrations in 0.5 M NaClO 4
medium at 298 K ([Sn 2+ ] tot = 0.5 to 10 mM). The evaluation of experimental data
2
3 4
2
2 2
indicated the formation of Sn (OH) + and Sn (OH) + .
Although no experimental data are reported, the work seems to have been done
correctly (the oxidation of tin(II) was checked with pirocatechol violet and found to be
negligible, data obtained below pH 1.2 were neglected). The authors suggested the
2
2 2
formation of Sn (OH) + as a minor hydrolysis product, which was rejected by the
reviewers based on the extensive data of [1958TOB] and [1976GOB] (see comment on
2
[1958TOB]). However, the formation of the complex Sn 2(OH) +
2 represents only a few
percent of the overall pH effect. Therefore the value reported for log β is
*
10 4,3
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012