Exploration of Boundary between Charge-Density-Wave and Mott–Hubbard States in Quasi-One-Dimensional Halogen-Bridged Metal Complexes

Abstract

Abstract In spite of a long history of quasi-one-dimensional halogen-bridged complexes (MX-chains), all Pt and Pd complexes form charge-density-wave (CDW) state (–X···M2+···X–M4+–X···), while all Ni complexes form Mott–Hubbard (MH) state (–X–Ni3+–X–Ni3+–X–), without exception. Although an interesting charge dynamics are expected at the boundary between the two states, no compound thus far reported forms both states. Thus, we have sought a phase boundary in bromo-bridged Pd compounds by decreasing Pd···Pd distance. In this article, we introduce the following two methods to decrease Pd···Pd distances: introduction of long alkyl chains which can afford attractive force between them, and partial substitution with smaller Ni ions, [Ni1−xPdx(chxn)2Br]Br2. In both systems, we have succeeded in realizing Pd3+ MH state. It has been revealed that the electronic state of bromo-bridged Pd compounds is determined by the Pd···Pd distances, in other words, CDW and MH states are stabilized when Pd···Pd distances are longer and shorter than 5.26 Å, respectively.