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|Type:||Artigo de periódico|
|Title:||4,4′-dithiodipyridine As A Bridging Ligand In Osmium And Ruthenium Complexes: The Electron Conductor Ability Of The -s-s- Bridge|
|Abstract:||The compounds [Ru(NH 3) 5(dtdp)](TFMS) 3, [Os(NH 3) 5(dtdp)](TFMS) 3, [(NH 3) 5Os(dtdp)Os(NH 3) 5](TFMS) 6, [(NH 3) 5Os(dtdp)Ru(NH 3) 5](TFMS) 3(PF 6) 2, and [(NH 3) 5Os(dtdp)Fe(CN) 5] (dtdp = 4,4′-dithiodipyridine, TFMS = trifluoromethane-sulfonate) have been synthesized and characterized by elemental analysis, cyclic voltammetry, electronic, vibrational, EPR, and 1H NMR spectroscopies. Changes in the electronic and voltammetric spectra of the ion complex [Os(NH 3) 5(dtdp)] 3+ as a function of the solution pH enable us to calculate the pK a for the [Os(NH 3) 5(dtdpH)] 4+ and [Os(NH 3) 5(dtdpH)] 3+ acids as 3.5 and 5.5, respectively. The comparison of the above pK a data with that for the free ligand (pK 1 = 4.8) provides evidence for the -S-S- bridge efficiency as an electron conductor between the two pyridine rings. The symmetric complex, [(NH 3) 5Os(dtdp)Os(NH 3) 5] 6+, is found to exist in two geometric forms, and the most abundant form (most probably trans) has a strong conductivity through the -S-S- bridge, as is shown by EPR, which finds it to have an S = 1 spin state with a spin-spin interaction parameter of 150-200 G both in the solid sate and in frozen solution. Further the NMR of the same complex shows a large displacement of unpaired spin into the π orbitals of the dttp ligand relative to that found in [Os(NH 3) 5(dtdp)] 3+. The comproportionation constant, K c = 2.0 × 10 5, for the equilibrium equation [Os IIOs II] + [Os IIIOs III] ⇌ 2[Os IIOs III] and the near-infrared band energy for the mixed-valence species (MMCT), [(NH 3) 5Os(dtdp)Os(NH 3) 5] 5+ (λ MMCT = 1665 nm, ε = 3.5 × 10 3 M -1 cm -1, Δν̄ 1/2 = 3.7 × 10 3 cm -1, α = 0.13, and H AB = 7.8 × 10 2 cm -1), are quite indicative of strong electron delocalization between the two osmium centers. The electrochemical and spectroscopic data for the unsymmetrical binuclear complexes [(NH 3) 5Os III(dtdp)Ru II(NH 3) 5] 5+ (λ MMCT = 965 nm, ε = 2.2 × 10 2 M -1 cm -1, Δν̄ 1/2 = 3.0 × 10 3 cm -1, and H AB = 2.2 × 10 2 cm -1) and [(NH 3) 5Os III(dtdp)Fe II(CN) 5] (λ MMCT = 790 nm, ε = 7.5 × 10 M -1 cm -1, Δν̄ 1/2 = 5.4 × 10 3 cm -1, and H AB = 2.0 × 10 2 cm -1) also suggest a considerable electron delocalization through the S-S bridge. As indicated by a comparison of K c and energy of the MMCT process in the iron, ruthenium, and osmium complexes, the electron delocalization between the two metal centers increases in the following order: Fe < Ru < Os.|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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