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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