Coordination States of Fe3+ and Fe2+ Dissolved in Organic Solvents

We spectroscopically investigated the coordination states of Fe2+ and Fe3+ dissolved in several organic solvents. Ultraviolet–visible (UV–vis) spectra and extended X-ray absorption fine structure (EXAFS) analyses revealed that Fe3+ forms [FeCl4]− complex in all the solutions. The EXAFS analysis suggests that Fe2+ forms [FeCl4]2− in N,N-dimethylformamide (DMF) and N-methylpyrrolidone (NMP) solutions while it forms [FeL6]2+ (L is solvent molecule) in ethylene glycol (EG) and methanol (MeOH) solutions. We interpreted the solvent dependence of the Fe2+ coordination state in terms of the L–Fe2+ interaction and Cl− solubility in solvent.