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g-value
76 5
4
3
2
6000
6000
4000
4000
2000
2000
0
0
-2000
-2000
100
150
200
250
300
350
magnetic field (mT)
Figure 32
EPR-spectrum of (Q
7
)
6
[
D
-SiW
11
O
39
Mn(H
2
O)] obtained in toluene (c = 1 mM) at a temperature of
T = 95 K; radiation frequency f = 8943.7 MHz.
For Fe-containing samples Fe-57 Mössbauer spectrometry is an additional convenient
analytic way to get insight into the electronic properties in this case first and foremost
the oxidation state. Mössbauer spectrometry is the excitation of the nucleus with
J
-
radiation. The excitation energy is a function of electron density at the nuclear site or in
other words Mössbauer spectrometry provides a means of measuring s-electron density
at the nucleus as expressed in the formula for the isomer-shift
G
:
'
R
§
·
ª
2
º
G
const
.
<
(0)
C
¨
¸
¬
¼
R
©
¹
Scheme 5:
Formula for the isomer shift
G
(mms
-1
); (
'
R/R): relative difference of nuclear radii between
excited nucleus and nucleus in its ground state;
2
<
(0)
: charge density at the nucleus given by the
square of the s-orbital wave function; C = constant term.
For
57
Fe the factor (
'
R/R) bears a negative sign so that
G
decreases with rising oxidation
state.
57
Fe Mößbauer spectra were recorded by Dr. Jörg Sutter on a WissEl Mößbauer
spectrometer (MRG-500) at 77 K in constant acceleration mode.
57
Co/Rh was used as
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