Tuning of electronic structures of quasi-one-dimensional bromo-bridged Ni(III) complexes with strong electron-correlation by doping of Co(III) ions, [Ni_1-xCo_x(Chxn)₂Br]Br₂

We have succeeded in synthesizing the Ni^III complexes doped by Co^III ions, [Ni_1-xCo_x(chxn)₂Br]Br₂ (x = 0, 0.043, 0.093, and 0.118) by using an electrochemical oxidation method. The single-crystal reflectance spectrum of x = 0.118 shows an intense CT band about 0.5 eV, which is lower than that of [Ni(chxn)₂Br]Br₂ (1.3 eV). The single-crystal electrical conductivities at room temperature of these compounds increase with increase of the amounts of doping of Co^III ions. In the ESR spectra, peak-to-peak line widths ΔH_pp at room temperature change about 600 G in [Ni(chxn)₂Br]-Br₂ to 200 G in x = 0.118. Such a large x dependence of ΔH_pp seems to be ascribed to the increasing contribution from the increasing Curie spins which have smaller line width. Therefore, we have tuned the electronic structures of quasi-one-dimensional bromo-bridged Ni^III complexes with strong electron correlations by doping of Co^III ions.