Complex Formation between Transition Metal Ions and Organic Solvents: Electron Spin Resonance Investigations

Abstract

THE electron spin resonance (ESR) technique provides a powerful tool for investigating transition metal complex formation in non-aqueous solutions. In recent work we have shown¹ that ESR and optical absorption spectra of different paramagnetic ions are changed when glycerol replaces water as a solvent. Both the variation in line width and the optical ‘red shift’ obtained suggest a change in crystal-field energy levels by spin-orbit mechanisms. Newer theories have linked octahedral–tetrahedral changes to these ligand-field effects on non-bonding d electrons². Thus, it might be of interest to investigate the ESR spectra of the chlorides of Mn²⁺, Fe³⁺ and Cu²⁺ in different organic solvents including dimethylsulphoxide (DMSO), dimethylformamide, formamide, acetone, glycerol and ethanol. These solvents were chosen to provide a varying dielectric constant and base strength since such parameters are known to affect the equilibrium between the octahedral and tetrahedral states.