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

A Discussion of selected references
375
[1980ORE/AND]
In connection with electroplating, the ionic composition and nature of discharging
species in a system containing protonated pyrophosphate complexes of tin were studied
by polarography at 25 °C in 0.333 M K 2 SO 4 solution under argon atmosphere. The
formation of the species Sn(H x P 2 O 7 ) x–2
2 6
and Sn(H P2O 7) x −
x 2
was detected with
increasing concentration of pyrophosphate ion. The rate constant and the transfer
coefficient of the cathodic reaction were studied. Numerical values of the stability
constants are not provided.
[1980ORE/AND2]
The complex formation between tin(II) and pyrophosphate ion has been studied by
potentiometric and spectrophotometric methods at 25 °C and in 0.333 M K 2 SO 4 solution
[Sn 2+ 4
] T = 1 mM, [ PO − 2 7
] T = 5 to 100 mM. Nine different pyrophosphato complexes
2+ x−4y
were identified ( SnH
x(P2O 7)
y
, with (x,y) = (0,1), (1,1), (2,1), (0,2), (1,2), (2,2),
(3,2), (4,2)) and the equilibrium constants of their formation reactions were calculated
4
(in case of SnH
2(P2O 7) −
2
two protonation isomers were reported). The data were used
to develop a bath for Sn electroplating. The protonation constants of pyrophosphate are
not given in the paper and were taken from an untraceable book (Yu. F. Zdanov,
Chemistry and technology of polyphosphates, Khimiya, 1979). Due to the relatively
strong association between alkali metal ions and the differently protonated
pyrophosphates, the protonation of pyrophosphate and the tin(II)-pyrophosphate
systems should be investigated under strictly identical conditions, and the potassium
complexes of pyrophosphate have to be taken into account at [K + ] T > 0.1 − 0.2 M. This
is not the case in [1980ORE/AND2]. Furthermore, the potassium sulfate is not an inert
background electrolyte, since the sulfate ion forms complexes with tin(II). Therefore the
constants reported in [1980ORE/AND2] are not considered any further in this review.
[1980PAN/DEN]
The blue-black modification of SnO is isostructural with the tetragonal form of PbO but
is the only example of a regular square-pyramidal tin(II) coordination. A neutron study
was undertaken to check this tin(II) configuration which finally was confirmed indeed.
SnO, tetragonal, P4/nmm, a 0 /Å = 3.8029(5), c 0 /Å = 4.8328(8) (neutrons,
293 K), Z = 2. Profile and integrated-intensity refinements at room temperature confirm
the regular square-pyramidal coordination of Sn(II), with Sn–O 2.224(8) Å. Final R for
the integrated-intensity refinement was 4.3% for 28 measured intensities. The thermal
expansion is less anisotropic than expected for a layer structure.
From the above unit cell parameters the density of SnO(tetr) is calculated to be
ρ = (6393.9 ± 2.7) kg·m –3 .
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012