An unusual Pd(III) oxidation state in the Pd-Cl chain complex with high thermal stability and electrical conductivity

• Published in: Dalton transactions : an international journal of inorganic chemistry 2021-02, Vol.50 (5), p.1614-1619
• Main Authors: Mian, Mohammad Rasel, Wakizaka, Masanori, Yoshida, Takefumi, Iguchi, Hiroaki, Takaishi, Shinya, Afrin, Unjila, Miyamoto, Tatsuya, Okamoto, Hiroshi, Tanaka, Hisaaki, Kuroda, Shin-Ichi, Breedlove, Brian K, Yamashita, Masahiro
• Format: Article
• Language: English
• Subjects: Chains; Crystallography; Electrical resistivity; Hydrogen bonds; Oxidation; Scanning tunneling microscopy; Seebeck effect; Single crystals; Thermal stability; Valence
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/d0dt03848b

The Pd(iii) oxidation state is unusual and unstable since it strongly tends to disproportionate. We synthesized the quasi-one-dimensional (1D) halogen-bridged Pd(iii)-Cl complex [Pd(dabdOH)2Cl]Cl2 (1-Cl; dabdOH = (2S,3S)-2,3-diaminobutane-1,4-diol) with multiple hydrogen bonds. From single-crystal X-ray diffraction, the bridging Cl- ions were located at the midpoint of the Pd-Cl-Pd moieties in the 1D chains, indicating that the Pd ions are in a Pd(iii) average valence (AV) state. Moreover, bright spots for the Pd(iii) dz2 orbitals in the upper Hubbard band above the Fermi level were observed every ∼5 Å using scanning tunnelling microscopy. These results clearly indicate that the Pd ions are in a Pd(iii) AV state in 1-Cl. In addition, 1-Cl has the highest thermal stability (470 K) among the Pd(iii) complexes reported and the highest electrical conductivity (0.6 S cm-1 at 300 K) among the 1D Pd-Cl chains reported so far.