Titanium-Oxide Host Clusters with Exchangeable Guests

摘要

A novel family of water-soluble, polyoxocationic titanium-oxide host–guest clusters are reported herein. They exhibit an unprecedented hexagonal prismatic core structure for hosting univalent cationic guests like K~(+), Rb~(+), Cs~(+) and H_(3)O~(+). Guest exchange has been studied using ~(133)Cs NMR, showing the flexible pore of a host permits passage of a comparatively larger cation and giving an equilibrium constant of ca. 13 for displacing Rb~(+) by Cs~(+). Attractive ion-dipole interaction, depending on host–guest size complementarity, plays a dominant role for the preferential encapsulation of larger alkali-metal cationic guests.