M³⁺ Lanthanide Chloride Complexes in “Neutral” Room Temperature Ionic Liquids:  A Theoretical Study

Abstract

The solvation of MCl n 3- n lanthanide chloride salts (La3+, Eu3+, and Yb3+; n = 3, 6, and 8) is studied by molecular dynamics simulations in two room-temperature ionic liquids which are “neutral” (Lewis acidity): [BMI][PF6] composed of 1-butyl-3-methyl-imidazolium+,PF6 - ions and [EMI][TCA] composed of 1-ethyl-3-methyl-imidazolium+,AlCl4 - ions. The simulations reveal the importance of the MCl6 3- complex, commonly observed in solid-state structures and in chloride-containing solutions. This contrasts with the gas phase where, according to QM calculations, MCl6 3- is unstable toward the dissociation of 1 to 2 Cl- ions. In the two studied solvents, the MCl n 3- n complexes with n = 3 to 6 remain bound during the simulation, while MCl8 5- complexes lose two Cl- anions and form MCl6 3-. The only exception concerns LaCl8 5- which dissociates to LaCl7 4- in [EMI][TCA] solution. The first shell of MCl3, MCl4 -, and MCl5 2- is mainly completed by solvent anions (about 3, 2, 1 PF6 - and 4, 3, 1 AlCl4 - anions, respectively for M = Eu), while the three studied MCl6 3- complexes are surrounded by a cage of 9−10 BMI+ or EMI+ cations, into which some solvent anions can be inserted. The results are important for our understanding of the solution state of trivalent actinide or lanthanide ions in room temperature ionic liquids.

Characterising the Electronic Structure of Ionic Liquids: An Examination of the 1‐Butyl‐3‐Methylimidazolium Chloride Ion Pair

“…[a] a [28,68] b [37] c [36,69] d [39] e [38] f [27] g [30] A [a] UA = united atom model; cc-pVTZ(-f) is a cc-pVTZ basis set with all the f functions removed.…”

Ionothermal synthesis and crystal structures of metal phosphate chains

“…It appears that the same holds true in ionothermal framework synthesis using transition metal acetates. This may be in part due to the ability of halide ionic liquids to form very stable complexes with metals, especially metal halides [46,47]. We explored several IL/metal acetate mixtures and found them to give mixed chain and 3D products (as discussed above) with the 3D phases favoured by longer heating times as observed by Rao et al [21] in the hydrothermal synthesis of zinc phosphates.…”

The simulation of imidazolium-based ionic liquids†

“…In a later study a number of force field models were examined and it was concluded that charges would need scaling before accurate mixing dynamics could be obtained. [25] The effects of charge scaling on solute-solvent interactions have also been examined; only minor effects on solvation patterns were determined after the point charges of a neutral solute were halved, [39] and thus it appears that for a solute the overall charge is more important than the internal charge distribution.…”