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

VII.2 Solid tin oxides and hydroxides 117
(see Appendix A) does not allow to estimate reliably the thermodynamic equilibrium
constant for Reaction (VII.10).
VII.1.4 Mixed hydroxido complexes of tin(IV)
Qualitative data on the formation of SnCl 5 OH 2– 2
, SnCl 4(OH) − 2
2 , SnCl 3(OH) −
3 and
2
SnCl 2(OH) −
4 detected by Mössbauer spectroscopy are reported in [1991KHR/ZAP]. In
[1983CHE/DID] the formation of SnF 5 OH 2– was detected by 19 F NMR spectroscopy.
Thermodynamic data are reported for mixed hydroxido complexes of tin(IV) in
[1968DEA/EVA], [1970KUR/MAR] and [1975KLI/BAR]. The increased solubility of
amorphous SnO 2 in NaF or HF solutions, as compared to pure water, was explained by
the formation of the complexes Sn(OH) 4–n F n (aq) and Sn(OH) 4F n−
n (n = 1 at 25 and
50 °C, n = 2 at 200 °C, see Appendix A) [1975KLI/BAR]. Based on their 19 F NMR
measurements, Dean and Evans [1968DEA/EVA] reported log10
K = 5.1 for the
2
equilibrium constant of the reaction SnF −
6 + OH – SnF 5 OH 2– + F – . Due to the
reasons mentioned in Appendix A, none of the reported constants can be used to derive
selected values.
VII.2 Solid tin oxides and hydroxides
VII.2.1 Introduction
There is only one stable tin(II) hydroxide which can be described as tin(II) hydroxide
oxide [1961DON/MOS]. Single crystals suitable for X-ray analysis of this material
were obtained and the structural formula was determined to be Sn 6 O 4 (OH) 4
[1968HOW/MOS]. This phase occurs in nature as a corrosion product of elemental tin
and has been named hydroromarchite [1971ORG/MAN], [1973HOW/MOS]. So far no
information on thermodynamic properties of Sn 6 O 4 (OH) 4 , qualifying for selection in
this review, is available.
Tin(II) oxide exists in several modifications. The thermodynamically stable
form at 298.15 K and 10 5 Pa is blue-black tetragonal SnO, which is the only example
for a regular square-pyramidal tin(II) coordination [1980PAN/DEN]. The name of the
naturally occuring mineral is romarchite, a pewter artefact [1971ORG/MAN],
[2003DUN/CRA].
Donaldson et al. [1961DON/MOS2] established the conditions under which the
metastable red orthorhombic modification can be prepared. A second red SnO was
prepared by Kwestroo and Vromans [1967KWE/VRO]. There is no systematic
thermodynamic investigation for the red tin(II) oxide phases, therefore, only values for
blue-black tetragonal SnO have been selected in this review.
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012