Coordination of Ln3+ in ortho-tetramethyl-substituted cucurbituril supramolecular assemblies formed in the presence of cadmium nitrate: potential applications for isolation of heavier lanthanides

Abstract

Coordination in supramolecular assemblies was investigated by reacting a series of lanthanide cations (Ln³⁺) and a new alkyl-substituted cucurbituril, the ortho-tetramethyl-substituted cucurbituril (o-TMeQ[6]), in the presence of cadmium nitrate as an inorganic structure inducer in neutral solution. X-ray diffraction analysis revealed that the coordination of lanthanide cations gives rise to two isomorphous groups bound to three and eight isomorphous compounds, respectively. One group is typical of the coordination of o-TMeQ[6] with light lanthanide cations such as Nd³⁺, Sm³⁺ and Eu³⁺, while the other group is characteristic of the coordination of o-TMeQ[6] with heavy lanthanide cations such as Gd³⁺, Tb³⁺, Dy³⁺, Ho³⁺, Er³⁺, Tm³⁺, Yb³⁺ and Lu³⁺. Most interestingly, no solid crystals were obtained for any compounds containing La, Ce, or Pr, suggesting that these compounds may be suitable for the separation of heavier lanthanide cations from their lighter counterparts.