Capsule–Capsule Conversion by Guest Encapsulation

Abstract

Guest-induced M18 L6 -M24 L8 capsule-capsule conversion is reported. Both capsules are composed of Pd(II) ethylenediamine units (M) and 1,3,5-tris(3,5-pyrimidyl)pyrimidine (L), and form trigonal bipyramidal (M18 L6 ) and octahedral (M24 L8) closed-shell structures with huge hydrophobic inner spaces. The M18 L6 trigonal bipyramid is converted to the M24 L8 octahedron through encapsulation of large aromatic guests, with the latter capsule possessing a cavity volume three times larger than the former. Despite the dynamic properties of the capsule host, the encapsulated guests are difficult to extract and are thus isolated from the external environment.

Design and Applications of Water-Soluble Coordination Cages

“…The Fujita group reported the conceptually similar guest-induced Pd 18 L 6 ( 212 ) → Pd 24 L 8 ( 213 ) cage–cage conversion in water ( Figure 59 ). 223 Both cages are closed-shell structures with large hydrophobic inner spaces composed of [Pd(en)] 2+ linking units bridged by 1,3,5-tris(3,5-pyrimidyl)pyrimidine ligands 214 . By mixing [(en)Pd(NO 3 ) 2 ] and 214 in water, Pd 18 L 6 trigonal bipyramidal cage 212 was obtained quantitatively; its composition and approximate D 3 h symmetry were confirmed by crystallographic analysis.…”

“…X-ray structures of 212 and ( 215 ) 4 ⊂ 213 complexes as well as structural formulas of the ligand and guests are shown. 223 …”

Self‐Assembly of Functional Discrete Three‐Dimensional Architectures in Water

“…In addition, guest encapsulation can also induce a transformation from one coordination complex to another; an established example being the guest‐templated conversion from a M 2 L 3 helicate to a tetrahedral M 4 L 6 host . More recently, Fujita and co‐workers have reported how hydrophobic guest binding could both induce the transformation of a water‐soluble bipyramidal M 18 L 6 capsule into a larger octahedral M 24 L 8 cage, as well as the transformation between an octahedral M 20 L 8 cage and bowl‐shaped M 8 L 4 cage …”

Stimuli‐Responsive Supramolecular Gels Constructed by Hierarchical Self‐Assembly Based on Metal‐Ligand Coordination and Host–Guest Recognition

“…In the past decades, metal coordination‐driven self‐assembly has been proven to be a highly efficient strategy for producing predesigned 2D and 3D architectures . The ingenious ligand design and the meticulous choice of metal ions make the assemblies feature well‐defined geometry and cavity, which have potential applications in the fields such as guest binding, catalysis, and molecular machines . However, these rigid metallosupramolecules have relatively poor solubility, which therefore limits their utilization.…”