Chemistry Reference
In-Depth Information
BF
ð Þ
4
DMF at 298 K in HS state
(right) and at 123 K in LS state (left), and the magnetic susceptibility as a function of temperature
for
Fig. 2.23 View of the crystal structure of Fe
I
2
pmatr
ð Þ
2
BF
4
Fe
I
2
pmatrz
ð
Þ
2
ð
Þ
4
DMF [
39
]
As seen from the 180 K spectrum the original quadrupole doublet (red) from [HS-
HS] pairs has totally disappeared at the favor of the poorly resolved LS quadrupole
doublet (blue) from [HS-LS] pairs and the new HS doublet (dark red) from [HS-LS]
pairs. Its quadrupole splitting is significantly smaller than that in the original [HS-
HS] pairs, and clearly points to the occurrence of a molecular distortion caused by the
spin transition. In other words, the ST occurring in one Fe
II
center is rapidly (in times
characteristic of molecular vibrations) transmitted through the bridging ligand to the
neighboring Fe
II
center where it causes some molecular distortion such that the
ligand field strength is weakened to such an extent that no more thermal SCO takes
place with this Fe
II
ion on further cooling. This is indicated in the structure (Fig.
2.23
)
by the black color for the Fe
II
center remaining permanently in HS state. Clearly,
Mössbauer spectroscopy has revealed such extreme subtleties in this study which is
hardly possible with any other physical technique.
2.3.2.4 Thermal Spin Transition in a Trinuclear Fe
II
Compound
CF
3
SO
ð Þ
6
(ip-
trz = 4-isopropyl-1,2,4-triazole) was synthesized and its structure and magnetic
The trinuclear Fe
II
compound of formula
Fe
3
iptrz
ð
Þ
6
H
2
ð Þ
6
