Chemistry Reference
In-Depth Information
Chapter 9
Crystal Structures and Properties
of MMX-Chain Compounds Based
on Dithiocarboxylato-Bridged Dinuclear
Complexes
Minoru Mitsumi
Abstract In this chapter, a comprehensive study of the syntheses, crystal
structures, and properties of the series of one-dimensional (1D) halogen-bridged
mixed-valence dimetal complexes, MMX-chain compounds, based on the
dithiocarboxylato-bridged dinuclear complexes, [Pt
2
(RCS
2
)
4
I]
1
(R
¼
Me (1), Et
(2),
n
-Pr (3),
n
-Bu (4),
n
-Pen (5), and
n
-Hex(6)) and [Ni
2
(RCS
2
)
4
I]
1
(R
Me (7),
Et (8),
n
-Pr (9), and
n
-Bu (10)) are described. The evolution from 1D halogen-
bridged metal complex, MX-chain compounds, to MMX-chain compounds has
produced a variety of electronic states and subtle balance of solid-state properties
originating from the charge-spin-lattice coupling and the fluctuation of these
degrees of freedom. With increasing the internal degrees of freedom originating
from the mixed-valence diplatinum unit, the Pt MMX-chain compounds except for
3 show relatively high electrical conductivity of 0.84-43 S cm
-1
at room tempera-
ture and exhibit metallic conducting behavior with
T
M-S
¼
¼
205-324 K. These
compounds at room temperature are considered to take the valence-ordered state
close to an averaged-valence (AV) state of -Pt
2.5+
-Pt
2.5+
-I
-
-. The analyses of the
diffuse scattering observed in the metallic state of 2 revealed that the metallic state
has appeared by the valence fluctuation accompanying the dynamic valence-order-
ing state of the charge-density-wave (CDW) type of -Pt
2+
-Pt
2+
-I
-
-Pt
3+
-Pt
3+
-I
-
-.
On the other hand, the metallic Pt MMX-chain compounds become insulators with
lowering temperature due to the lattice dimerization originating from an effective
half-filled metallic band. The synchrotron radiation crystal structure analysis of 2 at
48 K revealed that the valence-ordered state in the LT phase is the alternate charge-
polarization (ACP) state of -Pt
2+
-Pt
3+
-I
-
-Pt
3+
-Pt
2+
-I
-
-. Furthermore, the elonga-
tion of the alkyl chains introduces increasing motional degrees of freedom in the
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