53195-18-9Relevant articles and documents
Binuclear ruthenium complexes bridged by the dicyanamide anion
Sutton, James E.,Krentzien, Heinz,Taube, Henry
, p. 2842 - 2846 (1982)
As shown by the value of the extinction coefficient for the intervalence band for μ-dicyanamido-bis(pentaammineruthenium)(4+), ε 2.8 × 103 M-1 cm-1, dicyanamide ion as a bridging group produces quite strong electronic coupling in the mixed-valence molecule. A number of properties, among them the bandwidth at half-height, the dependence of the band energy on solvent properties, and the rather small value of the comproportionation constant, 3.4 × 102, show the species to be valence trapped. Replacing trans ammonias by pyridine or by isonicotinamide decreases the electronic coupling, suggesting that the dominant coupling mechanism, in spite of the negative charge on the ligand, is πd-π* delocalization rather than πd-π.
Donor-acceptor electronic coupling as a function of bridging group: Mixed-valence diruthenium(II,III) complexes bridged by isonicotinato and isonicotinamido ligands
Chou, Mei H.,Creutz, Carol,Sutin, Norman
, p. 2318 - 2327 (2008/10/08)
Binuclear, mixed-valence μ-isonicotinato and μ-isonicotinamido complexes capped by pentaammineruthenium(II) at the pyridine site and pentaammineruthenium(III) at the carboxylato or amido site have been synthesized and characterized. On the basis of their electronic absorption spectra and redox properties, the amido complexes are assigned as the N-bonded (RuIII-NHC(O)R) isomers. The mixed-valence complexes exhibit intervalence charge-transfer bands at 720 nm (ε = 2.6 × 102 M-1 cm-1) and 761 nm (0.9 × 103 M-1 cm-1), respectively, in aqueous acetate buffer at pH 4.8. The redox potentials of the two sites differ by 0.44 V in the isonicotinato and by 0.54 V in the isonicotinamido complexes in the above medium, and the donor-acceptor coupling elements, evaluated from the intensities of the intervalence bands, are 300 and 510 cm-1, respectively. Solvent dependences of the electronic spectra and electrochemical parameters are also reported. Both bridges provide significant coupling between the Ru(II) and Ru(III) metal centers in the mixed-valence complexes. These coupling energies serve as a point of departure for a consideration of coupling mechanisms in related polyproline-bridged systems for which thermal electron-transfer rates have been determined. It is concluded that hole transfer pathways predominate when osmium(II) pentaammine is the donor and cobalt(III) or ruthenium(III) pentaammine is the electron acceptor.
Aromatic sulfonation by SO32- and the reduction potential of the sulfite radical: Oxidation of sulfite by the tetraammine(phenanthroline)ruthenium(III) cation
Sarala, Rajeshuni,Islam, M. Ashraful,Rabin, Steven B.,Stanbury, David M.
, p. 1133 - 1142 (2008/10/08)
The reaction of [Ru(NH3)4(phen)]3+ (phen = 1,10-phenanthroline) with SO32- has been studied in aqueous solution at 25°C and μ = 0.1 M (NaCF3SO3). Above pH 8 the reaction is 2[Ru(NH3)4(phen)]3+ + SO32- + H2O → 2[Ru(NH3)4(phen)]2+ + SO42- + 2H+. Under more acidic conditions an additional reaction occurs: 2[Ru(NH3)4(phen)]3+ + SO32- → [Ru(NH3)4(phen)]2+ + [Ru(NH3)4(phen-SO3)]+ + H+, where phen-SO3 is 1,10-phenanthroline-4-sulfonate. The rate law is -d[Ru(III)]/dt = [Ru(NH3)4(phen)3+]{2k1[S(IV)]/(1 + [H+]/Ka) + 2kdQd(S(IV)]2/(1 + Ka/[H+])2} with k1 = (3.7 ± 0.2) × 104 M-1 s-1, kdQd = (3.2 ± 0.5) × 10-2 M-2 s-1, and Ka = (8.0 ± 0.9) × 10-8 M, where Ka is the acid dissociation constant of HSO3-. The product distribution follows a pH function quite different from the rate law, indicating that the rate-limiting step is the same for both sets of products. No sulfonation occurs in the presence of allyl alcohol, demonstrating that SO3- is an intermediate. In the proposed mechanism, the k1 pathway represents electron transfer from SO32- to Ru(III) to form SO3-, which can be further oxidized to SO42-. The mechanism of sulfonation is unclear, possibly occurring by attack of HSO3 or SO3. The reaction [Ru(NH3)4(phen)]2+ + SO3- → [Ru(NH3)4(phen)]3+ + SO32- was studied by pulse radiolysis, and its rate constant was found to be 1.0 × 108 M-1 s-1. Combining this rate constant with k1 and Ef for the [Ru(NH3)4(phen)]3+/2+ couple leads to a value of Ef = 0.72 V for the SO3-/SO32- redox couple. An effective self-exchange rate constant of 4 M-1 s-1 is derived for the SO3-/SO32- redox couple by use of the Marcus cross-relationship, and this is shown to be consistent with a major portion of the barrier arising from the "umbrella" distortional mode.
