Abstract
Research into stimuli-responsive controlled self-assembly and reversible transformation of molecular architectures has received much attention recently, because it is important to understand and reproduce this natural self-assembly behavior. Here, we report two coordination nanocapsules with variable cavities: a contracted octahedral V24 capsule and an expanded ball-shaped V24 capsule, both of which are constructed from the same number of subcomponents. The assemblies of these two V24 capsules are solvent-controlled, and capable of reversible conversion between contracted and expanded forms via control of the geometries of the metal centers by association and dissociation with axial water molecules. Following such structural interconversions, the magnetic properties are significantly changed. This work not only provides a strategy for the design and preparation of coordination nanocapsules with adaptable cavities, but also a unique example with which to understand the transformation process and their structure-property relationships.
Highlights
Research into stimuli-responsive controlled self-assembly and reversible transformation of molecular architectures has received much attention recently, because it is important to understand and reproduce this natural self-assembly behavior
Recognition of the reversible structural interconversion between such isomers or quasi-isomers will provide new approaches to broaden the preparation of metal-organic nanocapsules (MONCs) with different shapes, and an understanding of their structure–property relationships, such as host–guest recognition, drug delivery and release, and supramolecular catalysis[16,25,26]
Since the initial discovery by Atwood et al in 200535 of PgCnbased MONCs constructed from six PgCn units and 24 Cu2+ ions, a number of studies have demonstrated that PgCn can selfassemble into octahedral hexameric M24 (M=Mg, Co, Ni, Cu, and Zn)[36,37,38,39,40], spherical dimeric M8 (M=Co, Ni, Cu, and Zn)41–43, “rugby ball” shaped hexameric Ga1244 or mixed nanocapsules[45,46,47]
Summary
Research into stimuli-responsive controlled self-assembly and reversible transformation of molecular architectures has received much attention recently, because it is important to understand and reproduce this natural self-assembly behavior. We report two coordination nanocapsules with variable cavities: a contracted octahedral V24 capsule and an expanded ball-shaped V24 capsule, both of which are constructed from the same number of subcomponents The assemblies of these two V24 capsules are solvent-controlled, and capable of reversible conversion between contracted and expanded forms via control of the geometries of the metal centers by association and dissociation with axial water molecules. The number of known vanadium capsules is limited[55,56,57,58] and here we report an interesting example of solventresponsive assembly of coordination nanocapsule quasi-isomers with distinct geometries This includes a contracted octahedral capsule (V24-oct) with the inner cavity of 1000 Å3, and an expanded ball-shaped capsule (V24-ball) with inner cavity of 1400 Å3, from the same number of subcomponents including 24 vanadium centers and 6 pyrogallol[4]arene units (Fig. 1). These two V24 capsules represent an example of a metal displaying versatility and forming different PgCn-based hexamer capsules
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