Interpenetrated Cage Structures

Abstract

This Review covers design strategies, synthetic challenges, host-guest chemistry, and functional properties of interlocked supramolecular cages. Some dynamic covalent organic structures are discussed, as are selected examples of interpenetration in metal-organic frameworks, but the main focus is on discrete coordination architectures, that is, metal-mediated dimers. Factors leading to interpenetration, such as geometry, flexibility and chemical makeup of the ligands, coordination environment, solvent effects, and selection of suitable counter anions and guest molecules, are discussed. In particular, banana-shaped bis-pyridyl ligands together with square-planar metal cations have proven to be suitable building blocks for the construction of interpenetrated double-cages obeying the formula [M4 L8 ]. The peculiar topology of these double-cages results in a linear arrangement of three mechanically coupled pockets. This allows for the implementation of interesting guest encapsulation effects such as allosteric binding and template-controlled selectivity. In stimuli-responsive systems, anionic triggers can toggle the binding of neutral guests or even induce complete structural conversions. The increasing structural and functional complexity in this class of self-assembled hosts promises the construction of intelligent receptors, novel catalytic systems, and functional materials.

Donor‐Site‐Directed Rational Assembly of Heteroleptic cis‐[Pd2L2L′2] Coordination Cages from Picolyl Ligands

“…This observation impressively showed up the possibility of forming homoleptic cages with all four methyl groups on the same face of the Pd(picoline) 4 complex, when a suitable avenue is opened to a self‐assembly product of exceptional thermodynamic stability. As we observed in previous work, the anion‐templated formation of interpenetrated double‐cages can lead into such an energetic sink, here causing the system to override the pivotal steric control, in other cases leading towards heteroleptic cages.…”

Cages vs. Prisms: Controlling the Formation of Metallosupramolecular Architectures with Ligand Side‐Chains

“…When the phenanthrene groups are replaced by aliphatic n ‐butyl groups, cage‐like structures are observed instead. Overall our results are further evidence for the importance of ligand‐ligand interactions in metallosupramolecular chemistry.…”

PdII2L4-type coordination cages up to three nanometers in size

“…They display interesting host–guest chemistry 1e,f,16 and undergo self-catenation reactions to yield complex interlocked structures. 17,18 In addition, they have been studied in the context of medicinal inorganic chemistry. 19 In order to prepare cages with large cavities, relatively long and rigid ligands are required.…”