Pd(III) Mott–Hubbard Compounds - Material Designs and New Physical Properties in MX-and MMX-Chain Compounds - page 37

Chapter 4
Pd(III) Mott-Hubbard Compounds

S. Takaishi and M. Yamashita

4.1 Introduction

In spite of long history of MX-chain complexes, all Pt or Pd compounds are in
CDW state, without exception. We have recently succeeded in realizing Pd(III) MH
state by two methods, that is, one is the chemical pressure via long alkyl chains
introduced as counteranions, [Pd(en) 2 Br](C n -Y) 2

H 2 O, and the other is the partial
substitution with Ni(III) ions, [Ni 1 x Pd x (chxn) 2 Br]Br 2 . In both systems, it has been
revealed that Pd(III) MH state was realized by the chemical pressure acting in the
systems.

4.2 Realization of Pd(III) MH State by Means of Fastener Effect
Acting Between Alkyl Chains [ 1 ]

4.2.1 Crystal Structure of [Pd(en) 2 Br](C 5 -Y) 2 H 2 O

Crystal structures of ¼

dipentylsulfosuccinate) at 259 and 162 K are shown in Fig. 4.1a, b , respectively.
At both temperatures, the crystal structures were nearly the same. However, there
was a remarkable difference in the periodicity at the two temperatures. At 259 K,
the lattice parameters a and b were as twice as those at 162 K. At 259 K, the Pd
(1)-Br bond lengths were 2.512(3) and 2.497(3) ˚ , whereas the Pd(2)-Br bond
lengths were 2.783(3) and 2.777(3) ˚ . Since a Pd(II)-Br bond length is usually
longer than a Pd(IV)-Br one, Pd(1) and Pd(2) were assigned to Pd(IV) and Pd(II),

[Pd(en) 2 Br](C 5 -Y) 2 H 2 O (en ¼ ethylendiamine, C 5 -Y