Tadashi Matsubara

Some applications of cyclic voltammetry to the reactions and properties of ruthenium ammine complexes. Reduction potentials and rate studies

Received December 2, 1975 AIC508623 Formal reduction potentials (Ef) obtained by cyclic voltammetry in aqueous solution are reported for a series of pentaammineruthenium(II1) complexes, Ru(NH3)5L3+, and several tetraammine complexes Ru(NH~)&~+, where L is a substituted pyridine (py-X) or an organonitrile (R-CN). The nitrile complexes display more positive Ef values than do the pyridine complexes with n-unsaturated R groups giving the largest values. Among the pyridine complexes, electron-withdrawing substituents -X increase Ef, and this trend is attributed to a combination of Tand u-bonding effects. The CV technique is also used to measure the rates of hydration and dehydration of the carbonyl group of N-coordinated 4pyridinecarboxaldehyde and it is demonstrated that coordination to R u ( N H ~ ) ~ ~ + slows the acid-catalyzed hydration path by several orders of magnitude.

Solvent effects on the electronic spectra of the ruthenium(II) complexes Ru(NH3)2+6 and Ru(en)2+3. Evidence for charge transfer to solvent transitions

The spectral properties of Ru(NH3)2+6 and Ru(en)2+3 in aqueous solution and in several mixed solvents are reported. The higher energy absorption band of each is solvent dependent; these data are discussed in terms of a charge transfer to solvent assignment. It is shown that the diffuse model modification of the Franck–Platzman treatment of the charge transfer to solvent (c.t.t.s.) spectra of halide ions can be used with these cationic species as well. Application of this model shows that the c.t.t.s. band shifts in going from one solvent to another is more a function of the solvation energies of the oxidized and reduced species in the different solvents than of factors such as the differing Franck–Condon energies or electron solvation energies. The model also explains the lower energy of the c.t.t.s. band in the Ru(en)2+3 relative to that of Ru(NH3)2+6, regardless of solvent, in terms of the larger ionic radius of the former complex. In addition, the solvent studies of the Ru(NH3)2+6 reveal the presence of a low extinction coefficient absorption band at 310 nm which is assigned as the 1T2gâ†�1A1g ligand field transition. Calculations based on the energy of this band plus the 1T1gâ†�1A1g band at 390 nm give the crystal field parameters Δ= 26.8 × 103 cm–1 and B= 454 cm–1 for Ru(NH3)2+6.