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Fig. 9.28 Temperature
dependence of the magnetic
susceptibility of [Pt
2
(
n
-
PrCS
2
)
4
I]
1
(3)[
76
]. The
solid
line
represents the fitting to
estimate the impurity spin
concentration. The estimated
Curie spin concentration is
only 0.17 %
Fig. 9.29 Temperature
dependence of the magnetic
susceptibility of [Pt
2
(
n
-
BuCS
2
)
4
I]
1
(4)[
33
]. The
solid line
represents the fitting
to estimate the impurity spin
concentration. The estimated
Curie spin concentration is
only 0.14 %
plot below ca. 30 K, is assigned to paramagnetic centers originating from impurities
and/or lattice defects. The most striking feature is an abrupt drop in the
w
M
of 4 to
the spin-singlet state, with hysteresis, around the first-order RT-LT phase transition
from the AV state to the ACP state. The abrupt drop of
w
M
in 4 is quite similar to
spin-Peierls transitions. The observed magnetic behavior of 4, however, seems to be
well described not by the spin-Peierls transition but by the regular electronic Peierls
transition. This is suggested as the transition is the first order in nature, the transition
temperature is very high, and sharp increases in
and
S
are observed at the
transition [
33
]. As described in the crystal structure section, the valence-ordering
structures in the ground states of 2 and 4 can be regarded as an ACP state. However,
an abrupt drop in
r
w
M
has not been observed for 2, indicating that the spin degree of
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