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

A Discussion of selected references
405
fac/mer isomers. The CPMAS spectra of crystalline solids containing [SnX 6 ] 2– and cisor
trans-[SnCl 4 (H 2 O) 2 ] assisted these assignments. The NMR data yielded quantitative
estimates of the amounts of the various species in solution as a function of the tin
concentration from 0.1 mol·dm –3 , where the hydrated stannic ion, Sn 4+ (aq), is
predominant, to near saturation where auto-complexing results in complex anion
formation. Soluble hydrolysis products for which OH-bridged structures are proposed
were detected in solutions without added HCl or HBr and increase in amount when
NaOH is introduced. Solutions containing excess NaOH reveal [Sn(OH) 6 ] 2– which has a
chemical shift of – 590 ppm and exhibits the Raman frequencies: 552(ν 1 ), 425(ν 2 ),
290 cm –1 (ν 5 ), appropriate for octahedral (O h ) symmetry. The 119 Sn NMR spectra of
tin(IV) mixed halide aqueous solutions consisted of signals ranging from – 600 ppm
(H 2 O and Cl – ligands) to – 2000 ppm (Br – ligands), due to the series of species
represented by SnCl x Br y (H 2 O) z (where x + y + z = 6), and can be interpreted by relating
the chemical shift of the tin nucleus to the sum of ligand electronegativities in a given
complex. The solvent extraction of tin halides from aqueous acid solution by diethyl
ether or isobutyl methyl ketone was investigated and tin(IV) shown to be extracted in
the form of both molecular [SnX 4 (H 2 O) 2 ] and ion-pair H + (aq)[SnX 5 (H 2 O)] – complexes.
These species can also be generated in solution by adding small amounts of water to
[SnX 6 ] 2– in acetone. Conjoint use of NMR and Raman spectra enables the major species
in these systems to be determined and allows the ν(Sn–X) symmetric stretching
frequencies to be identified and assigned.
[1994STE/FOT]
The protonation of pyrophosphate and triphosphate have been studied by potentiometry
in (CH 3 ) 4 NCl, NaCl and KCl (I = 0 to 0.75 M) and at different temperatures (t = 5 to
45 °C). The authors reported reliable thermodynamic dissociation constants of
pyrophosphoric acid.
[1994YAN/SUI]
The nonstoichiometry of tin oxides, SnO 2-x , was studied between 694 and 990 K by
coulometric titration using solid state electrolytes (YSZ). The non-stoichiometry (x) and
1/6
the oxygen partial pressure ( p O2
) are related via the proportionality x ~ pO
− 2 .
A phase Sn 3 O 4 has been formed between 696-731 K. The Gibbs free energy change of
ο
formation of Sn 3 O 4 is given by Δ G (Sn 3 O 4 )/J·mol −1 = − 1,163,960 + 417.36 (T/K).
[1994YAM/KAM]
f
m
Yamaguchi et al. [1994YAM/KAM] measured the high temperature heat content of
SnSe over the temperature range of 700 to 1550 K using a drop calorimeter. They fitted
their high temperature heat content data using a mathematical function (Shmate) and
used the data on enthalpy of formation at 298.15 K (− 90.8 kJ·mol –1 ) from Gadzhiev et
al. [1960GAD/SHA] and the entropy of (89.5 J·K –1·mol –1 ) from [1991KNA/KUB].
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012