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

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.