Chemistry Reference
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Fig. 4.12 Optical
conductivity spectra in the IR
region (E
i
//c axis).
n
(N-H)
denotes the N-H stretching
mode of chxn ligand
As mentioned above, the length of
b
axis should obey the different correlation
depending on their electronic states. Thus, the deviation from the line when
x >
0.9
suggests that the electronic state changed at
x ¼
0.9.
4.3.3
IR Spectra of [Ni
1
x
Pd
x
(chxn)
2
Br]Br
2
IR spectra of [Ni
1
x
Pd
x
(chxn)
2
Br]Br
2
were measured using single crystals [
8
]. As
shown in Fig.
4.12
, in spectra of the pure Ni complexes, only a single
(N-H) peak
was observed at around 3,000 cm
1
, reflecting the averaged valence [Ni(III)] state.
In the spectra of the pure Pd complex, the
n
(N-H) peak is split into two peaks due to
the formation of the mixed valence [Pd(II) and Pd(IV)] state. In the spectra of the
mixed metal chains, splitting was observed when
x >
n
0.90. This result indicates
that, when
x <
0.90,
they are in a Pd(II)-Pd(IV) mixed valence state, or CDW state. Therefore, the Pd
ions change from Pd(III) MH to Pd(II)-Pd(IV) mixed valence states at
x
~0.9.
0.90, the Pd ions are in a Pd(III) MH state, whereas when
x >
4.3.4 Optical Conductivity Spectra of [Ni
1
x
Pd
x
(chxn)
2
Br]Br
2
Optical conductivity spectra for [Ni
1
x
Pd
x
(chxn)
2
Br]Br
2
are shown in Fig.
4.13
[
8
].
The pure Ni complex (
x ¼
0) exhibits a prominent sharp peak (A) at around 1.3 eV.
This peak was attributed to the LMCT transition from Br
p
z
orbitals to the Ni(III) d
z
2
orbitals. With an increase in
x
, peak A broadened, and another peak (B) appeared on
the lower energy side. When
x >
0.41, A disappeared, and B became dominant.
With a further increase in
x
, B shifted to lower energy, and when
x
exceeded 0.9, B
disappeared, and a higher energy peak (C) appeared.
There was a discontinuous change in energy between peaks B and C. The energy
of C for 0.9
< x <
1 is almost equal to that of the peak for the pure Pd complex
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