Difference of Coordination between Alkali- and Alkaline-Earth-Metal Ions to a Symmetrical α,α′,δ,δ′-Tetramethylcucurbit[6]uril

To explore differences in coordination between alkali- and alkaline-earth-metal ions and cucurbit[<i>n</i>]urils, a water-soluble α,α′,δ,δ′-tetramethylcucurbit[6]uril (TMeQ[6]) was used to synthesize a series of complexes and their supramolecular assemblies, based on the coordination of TMeQ[6] with alkali- and alkaline-earth-metal ions. The complexes and corresponding supramolecular assemblies were structurally characterized by single-crystal X-ray diffraction. Unlike cucurbituril (Q[6]), which formed the metal–Q[6] polymers based on the direct coordination of carbonyl oxygen atoms to the alkali-metal ions, TMeQ[6] formed metal–TMeQ[6] polymers based on the direct coordination of carbonyl oxygen atoms with the alkaline-earth-metal ions rather than the alkali-metal ions.