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 × 10-4 cm s-1 and 0.59, respectively. The formal potential, E°′', 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.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Renewable Energy, Sustainability and the Environment
- Surfaces, Coatings and Films
- Materials Chemistry