Chemistry Reference
In-Depth Information
Table 9.2 XPS Data for
[Pt
2
(RCS
2
)
4
I]
1
(R
¼
Me (1), Et
(2)),
together with those of
[Pt
2
(EtCS
2
)
4
] and [Pt
2
(EtCS
2
)
4
I
2
][
31
,
32
]
Binding energies/eV
a,b
Pt
2+
4f
7/2
Pt
3+
4f
7/2
Pt
2+
4f
5/2
Pt
3+
4f
5/2
Compound
References
[Pt
2
(MeCS
2
)
4
I]
1
(1)
72.9 (1.81)
74.4 (1.75)
76.2 (1.77)
77.7 (1.73)
[
31
]
[Pt
2
(EtCS
2
)
4
I]
1
(2)
72.41 (1.52)
73.68 (1.66)
75.69 (1.57)
77.04 (1.89)
[
32
]
[Pt
2
(EtCS
2
)
4
]
72.26 (1.39)
75.57 (1.39)
[
32
]
[Pt
2
(EtCS
2
)
4
I
2
]
73.74 (1.38)
77.05 (1.39)
[
32
]
a
Full width at half-maximum values (fwhm) for peaks are given in parentheses.
b
These values were corrected against C 1s peak using a value of 284.6 eV for C 1s peak.
9.2.4 Electronic Absorption Spectra
Electronic absorption spectra of 1-5 are very similar to one another. The electronic
absorption spectrum of [Pt
2
(EtCS
2
)
4
I]
1
(2) is, therefore, described as an example
of those spectra [
32
]. The electronic absorption spectrum of [Pt
2
(EtCS
2
)
4
I]
1
(2)is
shown in Fig.
9.10
in addition to the spectra for [Pt
2
(EtCS
2
)
4
] and [Pt
2
(EtCS
2
)
4
I
2
].
Spectral data are summarized in Table
9.3
. The dominant feature of the absorption
spectrum of 2 is an intense broad band centered at 7,900 cm
1
(0.98 eV) that is
absent from the spectra of [Pt
2
(EtCS
2
)
4
] and [Pt
2
(EtCS
2
)
4
I
2
]. Highly conducting 1D
molecular-based conductors are known to show two intermolecular charge-transfer
absorption bands, located at 7,000 ~ 11,000 and 2,000 ~ 4,000 cm
1
[
56
-
60
]. For
TCNQ (A) salts (
r <
¼
7,7,8,8-tetracyanoquinodimethane), the former
is usually attributed to a charge-transfer transition of the type, A
0
A
2
1) (TCNQ
A
A
(CT
1
), and the latter to the A
0
A
A
A
0
(CT
2
) transition. The energy of CT
1
is
largely determined by the Coulomb repulsion between electrons on the same
molecule, while electrical conductivity is related to the low energy CT
2
band.
Since the compound 2 has formally one unpaired electron per an MMX unit, the
lowest energy band can be attributed to the interdimer charge-transfer absorption
CT
1
,d
*
1
. This band extends to the infrared region, thus rela-
tively high-electrical conductivity can be expected for 2. The absorption maximum
energies of 1 and 2 are 7,500 and 7,900 cm
1
[
32
], whereas those of 3-5 are shifted
to higher energy of 9,300 cm
1
for 3 and 9,000 cm
1
for 4 and 5 [
35
,
55
]. The
absorption maximum energy of 3 that shows the semiconducting behavior at RT is
shifted to the highest energy. The bands observed near 17,700 and 24,600 cm
1
for
2 are assigned to d
*
0
d
*
2
*
1
d
s
s
d
s
s
s
*
s
(I) and d
s
*
d
p
* transitions, respectively, similarly to
assignment for 1 [
31
].
9.2.5 Transport Properties
9.2.5.1
[Pt
2
(MeCS
2
)
4
I]
1
(1)
The temperature dependence of the electrical conductivity and resistivity of
[Pt
2
(MeCS
2
)
4
I]
1
(1) parallel to the chain axis
b
are shown in Fig.
9.11
[
31
]. The
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