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

394
A Discussion of selected references
2
detected: SnP2PO − 6
7
, Sn(P2O 7) − 2
, SnHP2O − 5
7,
SnH 2 P 2 O 7 (aq), SnH(P2O 7) − 2
,
4
SnH
2(P2O 7) − 3
2
, SnH
3(P2O 7) −
2
2
and SnH
4(P2O 7) − 2
. Similarly to [1986TUR/KRA] the
complexation of pyrophosphate with sodium ion was not taken into account, therefore
the equilibrium constants reported in [1986TUR/KRA2] can only be regarded as
apparent formation constants (see also the discussion on [1991DUF/WIL]). The
graphically presented experimental data were combined with those reported in
[1986TUR/KRA], and were re-evaluated for the purposes of this review, to identify the
composition of the formed complexes. The formation constants for the hydroxido
complexes were calculated from the selected values of this review. The assumption of
nine complexes is sufficient to reproduce fairly well the c.a. 200 experimental data (the
2
species SnH 2 P 2 O 7 (aq) and SnH 4(P2O 7) −
2 were rejected). Although, most of the
complexes were identified in [1991DUF/WIL], too, the speciation is rather different
from that suggested in [1991DUF/WIL] (see Figure A-46).
[1987TUR/KRA]
Polarographic method was used to determine the stability of pyrophosphato complexes
of tin(II) in the pH range 0.90 to 4.45 under argon atmosphere (1 M NaClO 4 , 25 °C).
The concentration of the ligand varied between 1.8 and 70.0 mM, the tin(II)
concentration was 0.1 mM. The cathodic reduction of tin(II) was found to be quasireversible.
The authors reported the formation of identical complexes as in their earlier
potentiometric study [1986TUR/KRA2]. The method devised by DeFord and Hume was
used to calculate the formation constants of the complexes formed. The formation
constants derived from the polarographic [1987TUR/KRA] and potentiometric
[1986TUR/KRA2] data are in perfect agreement. The complexation of pyrophosphate
with sodium ion was not taken into account, therefore this work has similar limitations
to that discussed in [1986TUR/KRA] and [1986TUR/KRA2] (see also the discussion on
[1991DUF/WIL]).
[1989MAO/YOU]
119 Sn NMR spectra of SnCl 4·5H 2 O dissolved either in pure water (c Sn(IV) = 0.7 to 4.5 M)
or in HCl solutions (c Sn(IV) = 2.9 M, c HCl = 1 to 12 M). Due to the high concentration of
2
tin(IV) the complex SnCl −
6
is the unique species only in 10 to 12 M HCl solutions
([Cl – ] TOT /Sn(IV)] TOT > 7.4). The observed resonances were assigned to the species
4−n
SnCl
n(H2O)
6− n
(n = 1 to 6). Although, the authors mentioned the possible formation of
hydroxido complexes, the aqua and hydroxido complexes were regarded equivalent.
[1989MAO/YOU2]
Two-dimensional 119 Sn exchange spectroscopy was applied to study the kinetics of
hydrolysis of tin(IV)-chlorido complexes. 119 Sn EXSY (exchange spectroscopy) spectra
have been recorded for two solutions, 2 g SnCl 4·5H 2 O was dissolved either in (i) 2 cm 3
water or (ii) 4 M HCl (c Sn(IV) = 2.9 M). The authors use the word hydrolysis for the
reaction
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012