Amphiphilic Properties and Flexible Crystal Structure of Layered Hybrid Aluminosilicate KCS-11

We revealed that the hybrid layered material KCS-11 (|Na4·(H2O)5|[(CH3)8Si8Al4O20]) exhibited flexible adsorption ability for several molecules with different molecular sizes (methanol, ethanol, acetone, ethylene glycol, glycine, 1-hexanol, benzyl alcohol) and that a remarkable structural change with interlayer expansion occurred after the adsorption of these molecules. The crystal structures of KCS-11 adsorbing the seven types of molecules were determined via ab initio analysis using powder X-ray diffraction data to clarify the arrangement and conformation of each molecule between the layers. After adsorption, all the samples maintained high crystallinity, and the interlayer space expanded flexibly in response to the molecular size and conformation. Each molecule was regularly accommodated in the hollow with an effective diameter of ca. 4 Å × 6 Å formed on both surfaces of the layered framework, and the number of adsorbed molecules was estimated to be two for 1-hexanol and four for others. The position of –OH or ═O groups in the admolecules was close to the Na+ cation near the center of oxygen 6-rings in the framework, and interatomic distances were in a range of 2.3–2.9 Å. Vapor adsorption measurements of methanol, ethanol, and acetone at high saturated vapor pressures yielded ideal type-I isotherms without hysteresis, as observed in nanoporous materials. These results indicate that KCS-11 can be used as an adsorbent for amphiphilic molecules without significant thermal energy.