title: Dynamic equilibrium between a supramolecular capsule and bowl generated by inter- and intramolecular metal clipping.
abstract: The metal-induced self-assembly of a resorcin[4]arene derivative 1 that has four pyridine units as pendent groups and two equivalents of [M(dppp)(OTf)(2)] (M=Pd, Pt) results in a dynamic equilibrium between an interclipped supramolecular capsule 3 and an intraclipped bowl 4 in nitromethane, although the interclipped capsule 3 is formed as a sole adduct in chloroform/methanol and the intraclipped bowl 4 is formed exclusively in an aqueous phase. This demonstrates how metal-induced self-assembly can be tuned by subtle changes in the solvent system. The coexistence of the two structures in nitromethane was characterized by NMR spectroscopy and coldspray ionization mass spectrometry (CSI-MS). The crystal structure of the interclipped capsule 3 b, which is composed of two units of ligand 1 and four Pt(II) ions, reveals the capsule cavity to have nanoscale dimensions of 15x20 A. NMR spectra show that the dynamic equilibrium between 3 and 4 is dependent on concentration and temperature. Temperature-dependent (1)H NMR spectroscopy was carried out from 273 to 343 K to verify the thermodynamic parameters that control the dynamic equilibrium process; the conversion from the interclipped supramolecular capsule 3 a to the intraclipped bowl 4 a is entropically favored and enthalpically disfavored. The rotational barrier of the restricted rotation of pyridine units in the intraclipped bowl 4 was determined by line-shape analysis.
authors.affiliation: School of Chemistry, College of Natural Sciences, Seoul National University, Seoul 151-747, Korea.
authors.forename: Seong Jin
authors.initials: SJ
authors.lastname: Park
authors.forename: Dong Mok
authors.initials: DM
authors.lastname: Shin
authors.forename: Shigeru
authors.initials: S
authors.lastname: Sakamoto
authors.forename: Kentaro
authors.initials: K
authors.lastname: Yamaguchi
authors.forename: Young Keun
authors.initials: YK
authors.lastname: Chung
authors.forename: Myoung Soo
authors.initials: MS
authors.lastname: Lah
authors.forename: Jong-In
authors.initials: JI
authors.lastname: Hong