Over the last decade molecular containers have been increasingly studied within the context of complex chemical systems. Herein we discuss selected examples from the literature concerning three aspects of this field: complex host-guest behaviour, adaptive transformations of molecular containers and reactivity modulation within them.

Many examples exist of biological self-assembled structures that restructure in response to external stimuli, then return to their previous state over a defined time scale, but most synthetic investigations so far have focused on systems that switch between states representing energetic minima upon stimulus application. Here we report an approach in which triphenylphosphine is used as a chemical fuel to maintain CuI-based self-assembled metallosupramolecular architectures for defined periods of time. This method was used to exert control over the threading and dethreading of the ring of a pseudorotaxane’s axle, as well as to direct the uptake and release of a guest from a metal–organic host. Management of the amount of fuel and catalyst added allowed for time-dependent regulation of product concentration.

A porphyrin-edged metal-organic tetrahedron forms host-guest complexes containing 1-4 equiv of fullerene C, depending on the solvent employed. The molecules of C were bound anticooperatively within well-defined pockets; an X-ray crystal structure of three fullerenes inside the tetrahedron was obtained. Electrochemical measurements revealed that the electron-accepting properties of the fullerenes inside the capsules were altered depending on the mode of encapsulation. The binding of multiple fullerenes was observed to increase the electron affinity of the overall cluster, providing a noncovalent method of tuning fullerene electronics.

A focused library of potential hydrogelators each containing two substituted aromatic residues separated by a urea or thiourea linkage have been synthesised and characterized. Six of these novel compounds are highly efficient hydrogelators, forming gels in aqueous solution at low concentrations (0.03–0.60 wt %). Gels were formed through a pH switching methodology, by acidification of a basic solution (pH 14 to ≈4) either by addition of HCl or via the slow hydrolysis of glucono‐δ‐lactone. Frequently, gelation was accompanied by a dramatic switch in the absorption spectra of the gelators, resulting in a significant change in colour, typically from a vibrant orange to pale yellow. Each of the gels was capable of sequestering significant quantities of the aromatic cationic dye, methylene blue, from aqueous solution (up to 1.02 g of dye per gram of dry gelator). Cryo‐transmission electron microscopy of two of the gels revealed an extensive network of high aspect ratio fibers. The structure of the fibers altered dramatically upon addition of 20 wt % of the dye, resulting in aggregation and significant shortening of the fibrils. This study demonstrates the feasibility for these novel gels finding application as inexpensive and effective water purification platforms.

The combination of a bent diamino(nickel(II) porphyrin) with 2-formylpyridine and Fe(II) yielded an Fe(II) 4 L6 cage. Upon treatment with the fullerenes C60 or C70 , this cage was found to transform into a new host-guest complex incorporating three Fe(II) centers and four porphyrin ligands, in an arrangement that is hypothesized to maximize π interactions between the porphyrin units of the host and the fullerene guest bound within its central cavity. The new complex shows coordinative unsaturation at one of the Fe(II) centers as the result of the incommensurate metal-to-ligand ratio, which enabled the preparation of a heterometallic cone-shaped Cu(I) Fe(II) 2 L4 adduct of C60 or C70 .

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Subcomponent self-assembly generates dynamic combinatorial libraries of Zn4L6 cages whose composition is strongly affected by catenation and encapsulation.

The combination of ab ent diamino(nickel(II) porphyrin) with 2-formylpyridine and Fe II yielded an Fe II 4 L 6 cage.U pon treatment with the fullerenes C 60 or C 70 ,t his cage was found to transform into an ew host-guest complex incorporating three Fe II centers and four porphyrin ligands, in an arrangement that is hypothesizedt om aximize p interactions between the porphyrin units of the host and the fullerene guest bound within its central cavity.T he new complex shows coordinative unsaturation at one of the Fe II centers as the result of the incommensurate metal-to-ligand ratio,which enabled the preparation of aheterometallic coneshaped Cu I Fe II 2 L 4 adduct of C 60 or C 70 .Coordination-driven self-assembly has proven to be auseful tool in the preparation of intricate and functional chemical species,the structural complexity of which would be difficult to achieve by using conventional covalent chemistry. [1] Of particular recent interest are the three-dimensional coordination cages,which possess internal cavities suitable for guest binding. [2] Metal-organic cages may be designed to incorporate ligands that are not merely inert scaffolds,b ut which contain functionality that can interact with guest molecules selectively. [3] This approach has been used to design cage assemblies that bind specific guests,i ns ome cases altering their reactivity. [4] Metalloporphyrin-baseds ubunits for cages are particularly attractive owing to interactions between prospective guests and the large aromatic faces of the porphyrins. [5] In certain cases,t he same system of molecular building blocks can form different metal-organic structures under different conditions. [6] Fore xample,s ystems containing soft metal ions with flexible coordination spheres,such as Ag I and Hg II ,u ndergo structural rearrangement when prompted by achange in stoichiometry, [7] and anionic guests can induce the reconfiguration of ad ynamic library of components into different polyhedral architectures. [8] Herein, we show how maximization of p interactions between the bent porphyrinato nickel(II) groups of aF e II 4 L 6 host and its fullerene guest causes the host to reconstitute into an ew kind of Fe II 3 L 4 receptor for the fullerenes C 60 and C 70 . Furthermore,w ed emonstrate that the delicate balance of orthogonal supramolecular interactions in this system can lead to the expression of aheterometallic host-guest ensemble.T hese complexes are built from as addled Ni II metalloporphyrin subcomponent 1 that forms tetrahedral Fe II 4 L 6 assembly 2 when combined with Fe II and 2-formylpyridine (Scheme 1). On addition of C 60 or C 70 ,t his structure reconfigures into aF e II 3 L 4 cone-shaped host-guest complex C 60/70 &3.T his species can be modified through the incorporation of additional ancillary ligands to form heteroleptic species C 60/70 &3(phen). Through these observations,w ew ere also able to predict and observe the formation of heterometallic host-guest species C 60/70 &4 that incorporates both Cu I and Fe II metal centers into the...