Supramolecular Assemblies of Sulfonatocalixarenes with Phenanthroline: Factors Governing Capsule Formation versus Bilayer Arrangements

Four crystalline complexes were prepared by the inclusion complexation of the 1,10‐phenanthrolinium ion (Phen) with p‐sulfonatothiacalix[4]arene (TCAS) (2 from a solution at pH 1–2 and 4 from 1 M HCl) and with p‐sulfonatocalix[5]arene (C5AS) (3 from a solution at pH 1–2 and 5 from 1 M HCl) upon varying the acidity of the solution. By combining the results obtained for complexes 2–5 with those for our previously reported complex (1), p‐sulfonatocalix[4]arene (C4AS) complexed to Phen, it was revealed that p‐sulfonatocalixarenes (CASs) form “bis‐molecular” capsules (1, 2, and 3) around Phen at pH 1–2, whereas complexes 4 and 5 display distinct host–guest inclusion behavior at higher acid concentrations. The degree of compactness of the capsules increases with the enlargement of the calixarene cavity, which is affected significantly by both the penetration depth of Phen and the structure of the Phen dimer. Furthermore, the complexation behavior of TCAS/C5AS with Phen in 1 M DCl was investigated by using NMR spectroscopy, and was discussed in comparison with the previously reported results obtained from solutions at pH 2.0. Capsule conditions: p‐Sulfonatocalix[5]arene complexed a 1,10‐phenanthrolinium (Phen) guest in a vertical orientation at pH 1–2, and formed a solid‐state “bis‐molecular” capsule. In contrast, in 1 M HCl, the calixarene complexed Phen in a horizontal orientation (see figure), which prevented Phen from forming a bis‐molecular capsule.