XAFS STUDIES OF Ni, Ta AND Nb CHLORIDES IN THE IONIC LIQUID 1-ETHYL-3- METHYL IMIDAZOLIUM CHLORIDE / ALUMINUM CHLORIDE

The structure of anhydrous nickel, niobium and tantalum metal chlorides in ionic liquids IL) is important in the development of new electrochemical alloy deposition techniques. In order to understand the interactions of these metal ions with ionic liquids, we have investigated their structures in situ with X-ray Absorption Spectroscopy (XAS). The ionic liquid used in this study is 1-methyl-3-ethylimidazolium chloride (EMIC)/aluminum chloride (AlCl3) and is formed by the addition of the Lewis acid AlCl3 to the EMIC. The acid-base character of the IL can be changed by varying the ratio of the AlCl3 to EMIC and thus changing the concentration of Cl. This dramatically changes the structure of species formed when the metal chlorides dissolve in the solution. The coordination of NiCl2 changes from tetrahedral in basic solution to octahedral in acidic solution. The NiCl2 is also a stronger Lewis acid in that it can induce the aluminum chloride to share its chlorides in the strong acid solution forming a structure with six near Cl ions and 8 further away Al ions which share all the Cl ions surrounding the Ni 2+ . When Nb2Cl10, a dimer, is added to the acidic or basic solution, the dimer breaks up and forms two species. In the acid solution, two trigonal bipyramids are formed with five equal chloride distances while in the basic solution, a square pyramid with four chlorides forming a square base and one shorter axial chloride bond. Ta2Cl10 is also a dimer and breaks in half in the acidic solution and forms two trigonal bipyramids. However, in the basic solution the dimer divides in half but the specie formed is sufficiently acidic that it attracts two additional chloride ions and forms a seven coordinated tantalum specie.