title: A unique spherical molecular host with D2d symmetry. A novel intramolecular kinetic equilibrium in metal ion complexation between two crown ethers.
abstract: [formula: see text] A spherical host with D2d symmetry consisting of a tetrathia[3.3.3.3]paracyclophane and two 18-crown-6 moieties was synthesized. Its crystal structure shows a central cavity with a diameter of 1.96 A and a depth of 6.75 A. A Na+ ion could rest in the cavity center but prefers core binding to external binding in one of the crown units. An intramolecular kinetic equilibrium was reached with the Na+ ion switching between the two crown units with an energy barrier of 14.1 +/- 3 kcal/mol.
authors.affiliation: Department of Chemistry, National University of Singapore, Institute of Materials Research and Engineering, 3 Research Link, Republic of Singapore.
authors.forename: Jianwei
authors.initials: J
authors.lastname: Xu
authors.forename: Yee-Hing
authors.initials: YH
authors.lastname: Lai
authors.forename: Chaobin
authors.initials: C
authors.lastname: He