Conductometric and voltammetric studies on the bis(triphenyl phosphine) ruthenium(II) complex, cis-[RuCl2(L)(PPh3)2], where L: 2-(2′-pyridyl)quinoxaline

Conductometric investigation on the bis(triphenyl phosphine) ruthenium(II) complex, cis-[RuCl2(L)(PPh3)2] (A) (where PPh3: triphenyl phosphine and L: 2-(2′-pyridyl)quinoxaline, C13N3H9), in dimethylsulfoxide (DMSO) was performed at temperatures ranging from 25 to 50 °C. In addition, cyclic voltammograms of A were recorded on platinum working electrode in dichloromethane (DCM) and dimethylsulfoxide (DMSO) using n-tetrabutylammonium hexafluorophosphate (NBu4PF6) as supporting electrolyte at 25 °C. The molar conductivities (Λ) demonstrate that A behaves as uni-univalent electrolyte in DMSO over the whole temperature range. This behavior can be explained in terms of the replacement upon dissolution of chlorine and PPh3 ligands by DMSO molecules, and consequently, the formation of the ion-pair [RuCl(L)(PPh3)(DMSO)2]Cl [B+Cl−] which is dissociated in some extent. The Λ values were analyzed by means of the Lee–Wheaton conductivity equation in order to estimate the limiting molar conductivities (Λo) and the ion-pair association constants (KA) of [B+Cl−]. The limiting ion conductivities ( λ + o ) for the B+ ion were evaluated using n-tetrabutylammonium chloride (NBu4Cl) as “reference electrolyte”. The thermodynamic functions related with the ion association, such as Gibbs free energy ( Δ G A o ) , enthalpy ( Δ H A o ) , and entropy ( Δ S A o ) , were evaluated as well. The mobility of B+ was found to increase linearly with rising temperature and the consequent decrease of the viscosity (η) of DMSO. The KA and Δ G A o values indicate that the association of [B+Cl−] increases to some extent with the rise of the temperature followed by the decrease of the dielectric constant (e) of DMSO. The voltammetric experiments indicated that the couple Ru3+/2+ is reversible and diffusion controlled in DCM and completely irreversible in DMSO.