Assemblies of Alkaline-Earth-Metal Ions with o-Tetramethyl-Substituted Cucurbituril in the Presence of the Cadmium Tetrachloride Anion

o‐Tetramethyl‐substituted cucurbituril (o‐TMeQ[6]), a polydentate ligand, has been synthesized and isolated in a controlled manner by using a dimer of dimethyl‐substituted glycoluril and a dimer of unsubstituted glycoluril. Coordination assemblies have been investigated by reactions between alkaline earth cations and o‐TMeQ[6] in the presence of [CdCl4]2–, a structure inducer, in HCl aqueous solution. X‐ray diffraction analysis revealed that o‐TMeQ[6] coordinates with Ca2+ or Sr2+ and forms centrosymmetric tetranuclear assemblies in the presence of [CdCl4]2–. [CdCl4]2– typically produces the “honeycomb effect” by forming honeycomb‐like frameworks, which assist metal ions in coordinating to o‐TMeQ[6]. The driving forces of this effect are the “outer‐surface interactions” of cucurbit[n]urils. Coordination assemblies have been investigated by reactions between alkaline earth cations and o‐tetramethyl‐substituted cucurbituril (o‐TMeQ[6]) in the presence of [CdCl4]2–, a structure inducer, in HCl aqueous solution. [CdCl4]2– forms honeycomb‐like frameworks, which assist metal ions in coordinating to o‐TMeQ[6].