The Lanthanide Contraction beyond Coordination Chemistry

Abstract

The lanthanide contraction is conceptualized traditionally through coordination chemistry. Here we break this mold in a structural study of lanthanide ions dissolved in an amphiphilic liquid. The lanthanide contraction perturbs the weak interactions between molecular aggregates that drive mesoscale assembly and emergent behavior. The weak interactions correlate with lanthanide ion transport properties, suggesting new strategies for rare-earth separation that exploit forces outside of the coordination sphere.

Complexation Enhancement Drives Water‐to‐Oil Ion Transport: A Simulation Study

“…The amount of nitrate counterions (− e ) directly bound to each Ln III (+3 e ) is calculated to be around 2.9±0.5 for Ce 3+ and 2.9±0.6 for Yb 3+ , indicating that Ln III ions are nearly (∼97 %) charge neutralized by nitrates in organic phases. This decreases the electrostatic repulsion and allows the metalloamphiphile complexes to aggregate; a phenomenon that we recently investigated using small angle X‐ray scattering measurements . Very recently it was experimentally demonstrated that aggregates in metalloamphiphile‐in‐organic solutions are not strictly charge neutral …”

“…The organic solutions, prepared via liquid‐liquid extraction, contained 0.07 m Ln(NO 3 ) 3 in a 0.5 m N , N ’‐dimethyl‐ N , N ’‐dibutyl tetradecylmalonamide (DMDBTDMA, Scheme S1 in the Supporting Information) n ‐heptane oil phase, along with an amount of waters experimentally obtained . The four solutions were studied using all‐atom, explicit‐solvent MD simulations with a polarizable force field.…”

“…The four solutions were studied using all‐atom, explicit‐solvent MD simulations with a polarizable force field. To guarantee that our systems were well equilibrated, annealing simulations were performed followed by production simulations, which were run longer than the previous atomistic simulations using polarizable force field ,…”

“…For instance, the interactions between Ln III ‐centered aggregates have been found to be able to affect the morphologies of the Ln III ‐centered aggregates in organic phases: strong inter‐cluster interactions were able to drive large clusters with more than one lanthanide ions . Moreover, the difference in the ionic radius between Ce III and Yb III (the lanthanide contraction) has been shown to be able to manifest beyond their coordination spheres in driving the mesoscale ordering in organic phases and consequently influence the Ln III extraction efficiency . Water molecules also participate in the formation of Ln III ‐centered clusters in the organic solutions as illustrated in Figure b,d.…”

“…The mesoscale assembly plays a significant role in the ion transport . Moreover, we have shown that the lanthanide contraction is able to affect the mesoscale interactions in organic solutions and consequently influence the lanthanide extraction efficiency . However, lacking is a detailed molecular level structural study that understands how coordination interactions between extracted ions and individual donors contribute to the overall competitive solvation energetics between oil and water phases that drive ion transport.…”