Ligand Substituent Effects on Ruthenium(III/II) Redox Properties: An Advanced Inorganic Laboratory Experiment

TCE

The Chemical Educator

ISSN: 1430-4171 (electronic version)

Table of Contents

Abstract Volume 2 Issue 3 (1997), S1430-4171(97)03125-7

Ligand Substituent Effects on Ruthenium(III/II) Redox Properties: An Advanced Inorganic Laboratory Experiment

David Hathcock, Jill Morris, Jill Madden, and Spencer J. Slattery*

State University of West Georgia, Carrollton, GA 30118

Published online: 25 August 1997

Abstract. A convenient inorganic lab exercise is presented which exposes the student to the influence ligand substituents can have on a metal center's redox properties. Students prepare a series of compounds with the general formula [Ru(bpy)²(R¹,R²mal)](PF₆), where bpy is 2,2'-bipyridine and R¹,R²mal is an anionic diketone ligand with various R¹ and R²substituents. Each complex is prepared in a single synthetic step and the Ru(III/II) couple is characterized by cyclic voltammetry. The potential of the Ru(III/II) couple shifts with varying R¹ and R² across a range from 0.64 to 1.10 volts vs SSCE in the following order: (R¹ = R² = Me) < (R¹ = R² = Ph) < (R¹ = Me, R² = CF₃) < (R¹ = R² = CF₃). The inductive effects of the R-substituents on the Ru(III/II) couple are consistent with their electron donating/withdrawing properties. Hammett constants for the substituents provide an approximate measure of these effects. A linear relationship is observed when the Hammett constants are plotted against the Ru(III/II) potential. This lab exercise demonstrates the influence ligand substituents can have on a metal center's electron density and it applies a versatile electroanalytical method, cyclic voltammetry, to measure the substituent effects.

Key Words: Laboratories and Demonstrations; redox; ruthenium; Hammett; inorganic; substituents; bipyridine; diketonate; voltammetry; electrochemistry

(*) Corresponding author. (E-mail: sslatt@westga.edu )

Article in PDF format (45 KB )