Stabilization of Pd(iii) states in nano-wire coordination complexes

Abstract

In spite of a long history of quasi-one-dimensional halogen-bridged complexes (MX-chains), all Pt and Pd complexes form the charge-density wave (CDW) state (–X⋯M^II⋯X–M^IV–X⋯), while all Ni complexes form Mott–Hubbard (MH) states (–X–Ni^III–X–Ni^III–X–), without exception. We have succeeded in stabilizing the Pd(III) MH state for the first time by utilizing the following two methods: partial substitution with Ni(III) ions, [Ni_1−xPd_x(chxn)₂Br]Br₂, and chemical pressure via long alkyl chains introduced as counter-anions, [Pd(en)₂Br](C_n–Y)₂·H₂O. In both systems, it has been revealed that the electronic state of bromo-bridged Pd compounds are 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.