Chemistry Reference
In-Depth Information
Fig. 2.25 a Projection showing the crystal structure of [Fe
3
(iptrz)
6
(H
2
O)
6
](CF
3
SO
3
)
6
[
42
].
b Temperature dependent
57
Fe Mössbauer spectra of [Fe
3
(iptrz)
6
(H
2
O)
6
](CF
3
SO
3
)
6
[
42
]. The
yellow, red and green doublets correspond to HS
0
,HS
c
and HS
SC
, respectively. The blue signal
corresponds to LS
c
intensity of the blue LSc resonance signal. This 2:1 intensity ratio for HS
S
o
: LSc
(green to blue) remains on further lowering the temperature. The same 2:1
intensity ratio remains for HSo: HSc (yellow to red) at any temperature until they
entirely disappear after the ST is complete. The Mössbauer spectrum recorded at
120 K shows only the resonance signals for HS-LS-HS species. Clearly, the outer
Fe
II
-HS sites ''feel'' the process of thermal ST at the center, which is being
communicated through the three rigid 1,2,4-triazole bridges and cause a noticeable
structural distortion at the outer Fe
II
-HS sites without influencing the spin state.
This is another ''textbook example'' for the high sensitivity of Mössbauer
spectroscopy similar to the Mössbauer study of the
BF
ð Þ
4
•DMF
discussed above. The tiny small distortion felt by the outer Fe
II
-HS sites, which is
caused by the ST from HS to LS in the center, is hardly detectable by diffraction
techniques. Similarly, HS
$
LS relaxation effects that are not seen by magnetic
susceptibility measurements were detected at room temperature for the trinuclear
Fe
I
2
ð
pmatrz
Þ
2
