Single crystals of quasi-one-dimensional bromo-bridged Ni-Pd mixed-metal complexes with 2S, 3S-diaminobutane (bn) as an in-plane ligand, [Ni 1-xPdx(bn)2Br]Br2, were obtained by using an electrochemical oxidation method involving mixed methanol/2-propanol (1:1) solutions containing different ratios of [NiII(bn) 2]Br2 and [PdII(bn)2]Br2. To investigate the competition between the electron-correlation of the Ni III states, or Mott-Hubbard states (MH), and the electron-phonon interaction of the PdII-PdIv mixed valence states, or charge-density-wave states (CDW), in the Ni-Pd mixed-metal compounds, X-ray structure analyses, X-ray oscillation photograph, and Raman, IR, ESR, and single-crystal reflectance spectra were analyzed. In addition, the local electronic structures of Ni-Pd mixed-metal single crystals were directly investigated by using scanning tunneling microscopy (STM) at room temperature and ambient pressure. The oxidation states of [Ni1-xPd x(bn)2Br]Br2 changed from a M II-MIv mixed valence state to a MIII MH state at a critical mixing ratio (xc) of ∼0.8, which is lower than that of [Ni1-xPdx(chxn)2Br]Br2 (chxn=1 R,2R-diaminocyclohexane) (xc≈ 0.9) reported previously. The lower value of xc for [Ni1-xPdx(bn) 2Br]Br2 can be explained by the difference in their CDW dimensionalities because the three-dimensional CDW ordering in [Pd(bn) 2Br]Br2 observed by using X-ray diffuse scattering stabilizes the PdII-PdIv mixed valence state more than two-dimensional CDW ordering in [Pd(chxn)2Br]Br2 does, which has been reported previously.
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