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 >
suggests that the electronic state changed at x ¼
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
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-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 >
0.90. This result indicates
that, when x <
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