Chemistry Reference
In-Depth Information
Table 9.1 Transition temperature and the entropy gain at the phase transition in [Pt
2
(RCS
2
)
4
I]
1
[
47
]
LT phase
!
RT phase
RT phase
!
HT phase
D
(J K
1
mol
1
)
T
trs
(K)
D
trs
S
trs
S
(J K
1
mol
1
)
Compound
T
trs
(K)
References
[Pt
2
(MeCS
2
)
4
I]
1
(1)
a
5.25
0.07
373.4
[
48
]
[Pt
2
(EtCS
2
)
4
I]
1
(2)
b
180 and
230
0.21 and 0.13
[
49
]
[Pt
2
(
n
-PrCS
2
)
4
I]
1
(3)
209
14.6
358.8
10.0
[
50
]
[Pt
2
(
n
-BuCS
2
)
4
I]
1
(4)
c
213.5
20.09
323.5
7.46
[
51
]
[Pt
2
(
n
-PenCS
2
)
4
I]
1
(5)
d
207.4
49.1
324
0
[
52
]
[Pt
2
(
n
-PenCS
2
)
4
I]
1
(5)
e
220.5
52.4
a
No thermal anomalies at
T
M-S
¼
300 K and
T ¼
80 K.
b
Transport properties show a metal-semiconductor transition at
T
M-S
¼
205 K.
c
The additional small phase transition observed at 114 K.
d
Data for as-grown sample.
e
Data for the sample once heated above the RT-HT phase transition at 324 K and then supercooled.
A very broad higher order phase transition was detected around 170 K
Fig. 9.2 (a) 1D chain structure of [Pt
2
(EtCS
2
)
4
I]
1
(2) at 293 K with an atomic numbering scheme
and relevant interatomic distances [
32
]. (b) Packing diagram projected down the
b
axis. Thermal
ellipsoid set at the 50 % probability level.
defined by the four sulfur atoms. This Pt-Pt distance is intermediate between that of
[Pt
2
II
(EtCS
2
)
4
](d
8
d
8
) (2.764 (1)
˚
)[
53
]and[Pt
2
III
(EtCS
2
)
4
I
2
](d
7
d
7
) (2.582 (1)
˚
)[
32
]
and is nearly equal to that of 1 (2.677 (2)
˚
)[
28
]. This is consistent with that
the bond order of the Pt-Pt bond in 1 and 2 (d
8
d
7
) is formally one-half. Pt-I
distances are 2.982 (1) and 2.978 (1)
˚
, which are longer than those observed in
[Pt
2
III
(EtCS
2
)
4
I
2
] (average 2.764
˚
)[
32
] and are similar to those in 1 (average
2.978
˚
)[
28
]. The dominant structural feature of [Pt
2
(RCS
2
)
4
I]
1
is a twisting of
two PtS
4
planes from an eclipsed arrangement characterized by the twist angle. The
two PtS
4
planes of the dinuclear unit in 2 are twisted by ca. 23.0
at 293 K from the
eclipsed
D
4
h
structure. This results from the S
S distance (ca. 3.0
˚
) of the SCS
moiety being longer than the Pt-Pt distance (ca. 2.68
˚
)[
28
,
32
]. This twisting has
enabled the stretching of the Pt-Pt bond by changing the twist angle.
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