Electrochemical and spectroscopic studies of ytterbium in the aluminum chloride-1-methyl-3-ethylimidozolium chloride room temperature molten salt

UV-visible absorption spectroscopy and amperometric titration experiments indicate that the ytterbium(III) chloride is complexed as the ytterbium(III) hexachloride, [YbCl6](3-), in basic aluminum chloride-1-methyl-3-ethylimidazolium chloride molten salt, and [YbCl6](3-) can be reduced to Yb(II) species via a quasi-reversible one-electron charge-transfer process. The standard heterogeneous rate constant and cathodic transfer coefficient for the reduction of [YbCl6](3-) in 44.4/55.6 mole percent melt are 1.29 x 10(-4)cm s(-1) and 0.59, respectively. The formal potential, E degrees', of this redox reaction is dependent upon the pCl of the basic melt, suggesting the loss of one chloride ion from [YbCl6](3-) during reduction to produce [YbCl5](3-). In the basic melt, [YbCl5](3-) is slowly oxidized by some components of the melt. In acidic melt, Yb(III) is stable and can be electrochemically reduced to produce stable Yb(II) via a reversible one-electron charge-transfer process. The formal potential of the Yb(III)/Yb(II) redox couple in acidic melt is about 2.5 V more positive than the corresponding reaction in basic melt, indicating a significant change in the coordination sphere. Values of the Stokes-Einstein product measured for the Yb(III) and Yb(II) species in these melts are comparable to those of transition metal chloro complexes with the same overall charge in the same melt.