Chemistry Reference
In-Depth Information
Fig. 2.13 a Mössbauer spectra of Prussian blue and Turnbull's Blue [
21
]. b Mössbauer spectra
(77 K) of ''Prussian Blue'' prepared from (A)
57
Fe
III
(SO
4
)
3
(enriched) ? K
4
[Fe
II
(CN)
6
]
(unenriched) and (B)
57
Fe
II
Cl
2
(enriched) ? K
3
[Fe
III
(CN)
6
] (unenriched) [
22
]. The spectra
A and B are identical and are indicative of the Fe
III
cation outside the hexacyano complex. This
confirms the occurrence of fast electron transfer in preparation B
increases from iodine to fluorine. In the same ordering the 4s electron population
decreases and as a direct consequence the s-electron density at the iron nucleus
decreases, and due to the fact that
\ 0 for
57
Fe the isomer shift increases
R
a
R
g
from iodide to fluoride.
2.3.1.5 Prussian Blue vs. Turnbull's Blue
It has been stated in old textbooks of inorganic chemistry and hence it was rec-
ognized for many years that Prussian Blue and Turnbull's blue are different sub-
stances depending on their synthetic pathways [
20
]. However, a Mössbauer
experiment originally performed by Fluck et al. [
21
] has demonstrated that the two
end products prepared in different ways are chemically identical. In preparation A
they prepared Prussian Blue, Fe
III
4
3
;
by mixing equivalent amounts of
Fe
II
C
ð
6
4
:
Their Mössbauer spectrum shown in Fig.
2.13
a
reveals a singlet (dark grey) attributed to LS Fe
II
ions and a quadrupole doublet
(light grey) attributed to HS Fe
III
ions. In preparation B, they mixed ionic Fe
II
with
Fe
III
ionic Fe
III
Fe
II
C
ð
6
and
3
as shown in the Mössbauer
spectrum (Fig.
2.13
a). Indeed, a fast electron transfer occurs from Fe
II
to Fe
III
during mixing the two components, the rate constant for electron transfer being
3
and also obtained Fe
III
4
Fe
II
C
ð
6
C
ð
6