The lanthanide contraction effect and organic additives impact the coordination structures of lanthanide ions with symmetrical octamethyl-substituted cucurbit[6]uril ligands

Abstract

The reaction of symmetrical octamethyl-substituted cucurbit[6]uril (OMeQ[6]) with lanthanide ions (La³⁺, Ce³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Dy³⁺ and Ho³⁺) in an aqueous solution of hydrochloric acid in the presence of CdCl₂ afforded nine coordination compounds (1–9), which were classified into three different types. The X-ray crystallography of these nine coordination compounds reveals an interesting structural change, which can be attributed to the lanthanide contraction effect. In addition, the reaction of OMeQ[6] with Ho³⁺ in the presence of hydroquinone led to compound 10, in which OMeQ[6] successfully coordinated with Ho³⁺ ions due to the bridging role of the organic additive hydroquinone.