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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
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