pH-Dependent Formation of Molecular Capsules and Coordination Polymers

A previously elusive “molecular capsule” and various other structural motifs incorporating p -sulfonatocalix[4]arene are accessible by controlling the pH and by varying the stoichiometry of the calixarene relative to potential guest molecules and trivalent metal ions. The “molecular capsule” has monoprotonated 1-aza-18-crown-6 shrouded by two calixarenes, which hydrogen bond to aquated lanthanide ions. In contrast, the presence of 1-aza-15-crown-5 forms a complex devoid of the crown ether, with lanthanide ions directly bound to sulfonate groups. Also reported are a coordination polymer incorporating monoprotonated 1,4-diazabicyclo[2.2.2]octane in the cavity of one calixarene which forms chelate rings to lanthanide ions and the structure of a capsule with 4,13-diaza-18-crown-6 surrounded by two calixarenes which hydrogen bond to homoleptic aquated trivalent gallium ions.