Electrochemical studies of the bis (triphenyl phosphine) ruthenium(II) complex, cis -[RuCl₂(L)(PPh₃)₂], with L = 2-(2′-pyridyl)quinoxaline

Abstract

Electrochemical studies of the newly synthesized bis(triphenyl phosphine) ruthenium(II) complex, cis-[RuCl₂(L)(PPh₃)₂] (1, with L = 2-(2′-pyridyl)quinoxaline, C₁₃N₃H₉), were performed in acetonitrile (ACN). For this purpose, cyclic voltammograms (CVs) as well as electrochemical impedance spectra (EIS) were recorded on either glassy carbon (GC), platinum (Pt), gold (Au), or multi-walled carbon nanotube (MWCNT) electrodes. Qualitative examination of solutions of 1 in ACN was performed on the basis of conductivity measurements and electrospray ionization mass spectrometry (ESI–MS). The conductivity data suggest that 1 is a 1 : 1 type electrolyte in ACN. The ESI spectra further demonstrate that upon dissolution of 1 in ACN progressive replacement of chloro- and PPh₃-ligands by ACN occurs, leading to formation of [RuCl(L)(PPh₃)(CH₃CN)₂]⁺Cl⁻, [2 ⁺ Cl ⁻ ]. The CVs recorded for [2 ⁺ Cl ⁻ ] on various working electrodes demonstrate that the reversibility of the redox couple 2^{2 +/+} enhances with the order: Au < Pt < MWCNT < GC. The EI spectra verify that GC and MWCNT electrodes provide insignificant barrier for interfacial electron transfer since they afford less charge-transfer resistance.

Keywords:

• Conductivity
• Cyclic voltammetry
• Electrochemical impedance spectrometry
• Electrospray ionization mass spectrometry
• Ruthenium(II) complex

Acknowledgments

The authors thank Mrs S. Heusing and Mrs D. Schneider (TU Ilmenau). A.I. Philippopoulos thanks the special research account of the National and Kaposistrian University of Athens for the financial support (Kapodistrias program number: 70/4/9277). The mass spectrometric work in Prague was supported by the Academy of Sciences of the Czech Republic (Z40550506), the European Research Council (AdG HORIZOMS), and the Grant Agency of the Czech Republic (203/08/1487).