A DFT study has been carried out to explore the solvation of naked rare-earth (RE) cations (Yb³⁺and Nd³⁺) in “dry” and “humid” room-temperature ionic liquid (RTIL), 1,3-dimethyl-imidazolium⁺, PF₆^-, designated as [MMI]⁺[PF₆]^-. The entire solvation study was first explored in the gas phase and further extrapolated to water and IL medium employing continuum solvation models. As depicted in figure IL, in “dry” IL, the first solvation sphere is occupied by six PF₆^-anions followed by three [MMI]⁺ cations in the second solvation shell. The scenario in “humid” conditions differs as the neutral H₂O molecules are directly bonded with Ln³⁺ cations in the first solvation sphere followed by PF₆^-anions forming the second solvation sphere. Nd³⁺being relatively large, can acquire 9 and 10 coordination numbers (CN), whereas Yb³⁺has been optimized to 8 and 9 coordinated species. From the binding energy (BE) analysis, it is noticed that irrespective of the CN and medium of study, all the complexes have the highest BE in the gas phase, followed by IL, and the least in the water medium. Moreover, it is also evident that for both “dry” and “humid” IL complexes, Yb³⁺complexes have relatively higher BE than Nd³⁺complexes. The results can provide some constructive information for the complexation phenomena of RE cations using IL, which can be useful for the practical extraction of REs using IL.

<b>Figure IL.</b> Pictorial diagrams of the lanthanide complexes formed with ILs in “dry” and “humid” conditions.

Figure IL. Pictorial diagrams of the lanthanide complexes formed with ILs in “dry” and “humid” conditions.

TAMALIKA ASH

Appearances