PNNL

Abstract

We report details of the coordination environment about Cu(II) in a pure ionic liquid, 1- ethyl-3-methylimidazolium chloride ([EMIM]Cl) and in mixtures containing varying amounts of water from 0-100% of the [EMIM]Cl. There are many stages in the ion pairing of the divalent cation, Cu(II) including the contact ion pairing of Cu2+ with multiple Cl- to form various CuCln (2-n) polyanions. Thereis also the subsequent solvation and ion pairing of the polychlorometallate anion with the EMIM+ cation. Using a combination of x-ray absorption fine structure (XAFS), UV-Vis spectroscopy and electronic structure calculations (TDDFT) we are able to follow the detailed structural changes about Cu(II). Ion pair formation is strongly promoted in [EMIM]Cl by the low dielectric constant and by the extensive breakdown of the water hydrogen bond network in [EMIM]Cl/water mixtures. In the [EMIM]Cl solvent the CuCl4 2- species dominates and it’s geometry is quite similar to gas-phase structure. These results are important in understanding catalysis and separation processes involving transition metals in ionic liquid systems.