Mixed-valence Sate of Binuclear Ruthenium Complexes Linked by Polyyne-Cumulene Resonance Spacer

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1.Geometry optimization (with no symmetry constraint) of some oxidized species of the model complex of a C_4-bridged binuclear β-diketonatoruthenium complex was successful, using the ADF program. The excitation energy was calculated by time-dependent DFT(TDDFT) using the Gaussian 98 program. The result of the TDDFT calculation of the Ru^<IV>-Ru^<III> species reproduces an intense absorption band at near 1620 nm (6170 cm^<-1>) with an oscillator strength (f=0.440) assigned as a mixture of MMCT and MLCT transitions.2.Low-temperature spectroelectrochemical cell was made. The Ru^<IV>-Ru^<III> state of C_6 and C_8-bridged binuclear β-diketonatoruthenium complexes in CH_2Cl_2 could be characterized by low-temperature spectroelectrochemistry. A relatively intense broad IVCT band in the near-IR region was observed for both complexes. Analyses of the IVCT bands indicate that wavenumber at absorption maximum is shifted to higher wavenumber and intensity of the band reduces with increasing the number of acetylene linkers.3.Temperature dependence of the magnetic susceptibility of CH_2Cl_2 solution of C_4-bridged binuclear β-diketonatoruthenium complex indicates that spin-spin interaction is antiferromagnetic below 20K and therefore ground state of the complex is singlet.4.Spectroelectrochemistry of binuclear β-diketonatoruthenium complexes bridged by tetraacetylethanato containing no spacer exhibits no significant IVCT band.