Mixed-valence states of rotaxane metal complexes

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(1) Tow novel mononuclear (β-diketonato)ruthenium(III) complexes with long conjugated chain composed of alternative ethynyl and aromatic groups at 3-carbon in 2, 4-pentandionato chelate have been prepared.Furthermore, two novel binuclear (β-diketonato)ruthenium(III) complexes have been prepared by oxidative coupling reactions of the ethynyl groups in the novel mononuclear complexes. Reaction of the oxidative coupling in the presence of cyclodextrin gave unidentified ruthenium species which exhibited visible spectrum similar to the corresponding binuclear complexes.(2) The binuclear ruthenium complexes with the alternative spacers exhibited two overlapping one-electron oxidation and reduction steps on the cyclic voltammograms. The two oxidation and reduction steps can be assigned to the oxidation of ruthenium(III) to ruthenium(IV) and to the reduction of ruthenium(III) to ruthenium(II), respectively. These results indicate that electrochemical interactions between metals in the Ru^<IV>- … More Ru^<III> mixed-valence state of the binuclear complexes with two aromatic rings in the spacer are considerably smaller than that of the corresponding binuclear complexes with only one aromatic ring.(3) Single crystal structure analysis has been carried out on a butadiynyl bridged (β-diketonato)ruthenium(III) dimmer(1). Strong electronic coupling over 1.3 nm distance has been observed for the one-electron oxidized state. The fully delocalized (Class III mixed-valent) system 1^+ is distinguished by an extremely intense (ε = 25000 mol^<-1> dm^3 cm^<-1>) inter-valence charge transfer (IVCT) band at 1730 nm and a single intense vibrational band at 2078 cm^<-1> associated with contributions from cumulene resonance structures.(4) A novel oxalate-bridged binuclear ruthenium(III) complex, [{Ru(acac)_2}_2(μ-ox)] (acac^- = acetylacetonate and ox^<2-> = oxalate), has been prepared via self-dimerization of K[Ru(acac)_2(ox)] in aqueous solutions containing ferric salts as catalyst. The Ru^<III>-Ru^<II> mixed-valence species generated electrochemically with K_c = 10^<5.0> for the comproportionation constant exhibits a weak IVCT band at 1430 nm. IR spectra from spectroelectrochemistry indicated a partially localized mixed-valence state. Less