Chemistry Reference
In-Depth Information
[Pt
2
(RCS
2
)
4
](R
Me, Et,
n
-Pr,
n
-Bu,
n
-Pen) can be stored without decomposition
for several months under an inert atmosphere in a freezer but gradually decompose
upon exposure to air.
The precursor complex [Pt
2
II
(MeCS
2
)
4
] readily undergoes oxidative addition
with halogens in hot toluene, giving [Pt
2
III
(MeCS
2
)
4
X
2
] containing platinum
atoms with formal oxidation state of
¼
þ
¼
3[
28
]. In the case of X
I, if the reaction
¼
is carried out with a ratio of [Pt
2
(MeCS
2
)
4
]:I
1:1, an MMX-chain compound
[Pt
2
(MeCS
2
)
4
I]
1
(1) with formal oxidation state of
2.5 is isolated. This compound
can also be obtained from the reaction of [Pt
2
II
(MeCS
2
)
4
] and [Pt
2
III
(MeCS
2
)
4
I
2
]in
toluene under reflux [
28
]. As described in the next section, [Pt
2
(MeCS
2
)
4
I]
1
(1)
undergoes an order-disorder type phase transition associated with the conformation
of two PtS
4
planes around 371-372 K [
46
]. One should be careful because the
disordered diplatinum unit of 1 will be partially formed in the crystal when the
crystals start to deposit above the transition temperature. [Pt
2
(RCS
2
)
4
I]
1
(R
þ
Et (2),
n
-Pr (3),
n
-Bu (4), and
n
-Pen (5)) can also be prepared by mixing equimolar
amounts of [Pt
2
II
(RCS
2
)
4
] and [Pt
2
III
(RCS
2
)
4
I
2
][
32
-
35
]. [Pt
2
(
n
-BuCS
2
)
4
I]
1
(4)
and [Pt
2
(
n
-PenCS
2
)
4
I]
1
(5) are prepared by cooling the corresponding toluene—
n
-hexane or
n
-hexane solution down to 2 ~ 0
C, because the solubility of the MMX
compounds increases with elongation of the alkyl chains. These MMX-chain
compounds are relatively stable in air.
¼
9.2.2 Crystal Structures
Before describing the crystal structures, the transition temperature and the entropy
gain at the phase transition obtained by the heat capacity measurements of
[Pt
2
(RCS
2
)
4
I]
1
(Me (1), Et (2),
n
-Pr (3),
n
-Bu (4), and
n
-Pen (5)) are listed in
Table
9.1
[
47
-
52
].
9.2.2.1
[Pt
2
(RCS
2
)
4
I]
1
(R
¼
Me (1), Et (2))
Miyazaki et al. have reported the heat capacity of [Pt
2
(MeCS
2
)
4
I]
1
(1) in which a
distinct heat capacity peak due to a phase transition was observed at
T
trs
¼
373.4 K,
indicating the presence of the room temperature (RT) and high-temperature (HT)
phases [
48
]. On the other hand, DSC measurements of [Pt
2
(EtCS
2
)
4
I]
1
(2) do not
show any latent heat in the temperature range of 150-473 K [
32
]. [Pt
2
(RCS
2
)
4
I]
1
(R
Me (1), Et (2)) crystallize in the same monoclinic space group
C
2/
c
and hence
have similar structures [
28
,
32
]. The crystal structure of 2 is shown in Fig.
9.2
.
The crystals of both compounds consist of neutral 1D chains with a repeating
-Pt-Pt-I- unit lying on the crystallographic twofold axis parallel to the
b
axis.
The crystal structure is exemplified with that of the compound 2 [
32
]. Two platinum
atoms of 2 are bridged by four dithiopropanato ligands with a Pt-Pt distance of
2.684 (1)
˚
¼
at 293 K, 0.189
˚
shorter than the distance between the mean planes
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