Controlled Self-Assembly and Multistimuli-Responsive Interconversions of Three Conjoined Twin-Cages

Abstract

Stimuli-responsive structural transformations between discrete coordination supramolecular architectures not only are essential to construct smart functional materials but also provide a versatile molecular-level platform to mimic the biological transformation process. We report here the controlled self-assembly of three topologically unprecedented conjoined twin-cages, i.e., one stapled interlocked Pd 12 L 6 cage (2) and two helically isomeric Pd 6 L 3 cages (3 and 4) made from the same cis-blocked palladium corners and a new bis-bidentate ligand (1). While cage 2 features three mechanically coupled cavities, cages 3 and 4 are topologically isomeric helicate-based twin-cages based on the same metal/ligand stoichiometry. Sole formation of cage 2 or a dynamic mixture of cages 3 and 4 can be controlled by changing the solvents employed during the self-assembly. Structural conversions between cages 3 and 4 can be triggered by changes in both temperature/solvent and induced-fit guest encapsulations. Well-controlled interconversion between such topologically complex superstructures may lay a solid foundation for achieving a variety of functions within a switchable system.

Increasing structural and functional complexity in self-assembled coordination cages

“…Interlocking as key structural motif was described for a variety of interpenetrated cages, 56,57 resulting in multi-cavity assemblies with different nuclearities and topologies, such as [Pd 4 L 8 ] double cages, 56,57 a [Pd 6 L 8 ] peanut-shaped system, 58 a huge [Pd 8 L 16 ] catenane, 59 or a [Pd 12 L 6 ] conjoined twin-cage. 60 Recently, we contributed a [Pd 2 L 4 ] host with a new mechanically-interlocked motif, consisting of a pair of doubly-interlocked, figure-eight-shaped lemniscates. 30 Even higher complexity was reported by Lützen and co-workers, with a rotaxane-like cage-in-ring structural motif, where a BODIPY-based bis-pyridine ligand ( 1 ) self-assembles with Pd II cations to form a compound of [Pd 6 1 12 ] stoichiometry ( Fig.…”

Transformation networks of metal–organic cages controlled by chemical stimuli

“…29 ). 162 Interlocked S 6 -symmetric cage 259 is the sole product observed from self-assembly of the BF 4 − salt of 262 with 2 equiv. of cis -protected [(tmen)Pd II (NO 3 ) 2 ] (tmen = tetramethylethylenediamine) in D 2 O, whereas a mixture of the two smaller isomeric cages 260 and 261 is obtained when acetone is introduced during the self-assembly process.…”

Light-Powered Dissipative Assembly of Diazocine Coordination Cages

“… 1 − 4 Response to external stimuli can then be employed to trigger structural rearrangements, affecting the host–guest binding affinity, thus establishing control over guest uptake and release. 5 − 12 Among various stimuli (e.g., pH, 13 − 15 temperature, 16 solvent, 17 electrochemical, 18 , 19 or chemical input 20 , 21 ), light is a highly advantageous reagent, as it can be precisely administered with temporal and spatial resolution, is available from cheap LED sources, and is essentially waste-free. The light-triggered modification of structure and function of (supra)molecular systems can be achieved using dedicated photoswitches such as azobenzenes, 22 , 23 dithienylethenes, 24 , 25 other hindered alkenes, 26 , 27 indigoids, 28 and spiropiranes, 29 , 30 just to name a few.…”