Understanding the Dynamics of Eu3+ Ions in Room-Temperature Ionic Liquids - Electrochemical and Time-Resolved Fluorescence Spectroscopy Studies

To understand the oxidation state, coordination geometry, and physicochemical behavior of the Eu3+ complex with dihexyl N,N-diethylcarbamoylmethylphosphonate (DHDECMP) in the ionic liquid (IL) 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][NTf2]), the spectroscopic and electrochemical properties of the system were investigated. The electrochemical behavior of Eu3+-DHDECMP in [bmim][NTf2] was studied by cyclic voltammetry (CV) and chronoamperometry at a glassy carbon (GC) electrode. The reduction of Eu3+ to Eu2+ in [bmim][NTf2] is quasireversible and controlled by diffusion as well as charge-transfer kinetics. Photoluminescence spectroscopy confirms that the symmetry around the europium ions in Eu3+-DHDECMP in the room-temperature IL (RTIL) is relatively low; this is further supported by calculations of the Judd-Ofelt parameters ((2) higher than (4)). On the basis of fluorescence lifetime measurements, the number of water molecules in the inner sphere is six for uncomplexed europium ions, and practically no water molecules are retained in the presence of the complexing extractant DHDECMP.