Multilevel coordination-driven assembly for metallosupramolecules with hierarchical structures

Exploiting reduced-symmetry ligands with pyridyl and imidazole donors to construct a second-generation stimuli-responsive heterobimetallic [PdPtL4]4+ cage

A new sequential metalation strategy that enables the assembly of a new more robust reduced symmetry heterobimetallic [PdPtL4]4+ cage C is reported. By exploiting a low-symmetry ditopic ligand (L) that features imidazole and pyridine donor units we were able to selectively form a [Pt(L)4]2+ "open-cage" complex. When this was treated with Pd(ii) ions the cage C assembled. 1H and DOSY nuclear magnetic resonance (NMR) spectroscopy and electrospray ionisation mass spectrometry (ESIMS) data were consistent with the quantitative formation of the cage and the heterobimetallic structure was confirmed by single crystal X-ray crystallography. The cage C was shown to bind anionic guest molecules. NMR studies suggested that these guests interacted with the cavity of the cage in a specific orientation and this was confirmed for the mesylate ion (MsO-) : C host-guest adduct using X-ray crystallography. In addition, the system was shown to be stimulus-responsive and could be opened and closed on demand when treated with appropriate stimuli. If a guest molecule was bound within the cage, the opening and closing was accompanied by the release and re-uptake of the guest molecule.

Hierarchical packing of racemic metallosupramolecular cages with Ni(II)-based triple-stranded helicate building blocks

Three novel hierarchical Ni-based metallosupramolecular cages were constructed from nickel ions, pyridine dicarboxylates and isophthalate derivative ligands (the substituents on C5 of isophthalate are methyl, tert-butyl and bromo groups). In every cage, two multinuclear nickel clusters, assembled from four nickel atoms and three pyridine dicarboxylate ligands, are interlinked by three isophthalate-derivative ligands to form a nickel-based triple-stranded helicate (TSH), which then becomes the supramolecular building block for the fabrication of a metallocage. Six homochiral TSH supramolecular building blocks, either left (M)-handed or right (P)-handed, are connected by four linking nickel atoms to generate M6 and P6 discrete racemic cage molecules (M6 - cage with six M-TSHs; P6 - cage with six P-TSHs). The crystal packing of the racemic cages was characterized by single-crystal X-ray diffraction. An additional cobalt-based molecular cage with 5-methylisophthalate bridging ligands was synthesized for host-guest interaction studies. The methyl groups in Co- and Ni-TSH can act as guest units to be accommodated in the cone-shaped metal clusters (host) of an adjacent cage.

Single-Crystal Superstructures via Hierarchical Assemblies of Giant Rubik's Cubes as Tertiary Building Units

Intricate superstructures possess unusual structural features and promising applications. The preparation of superstructures with single-crystalline nature are conducive to understanding the structure-property relationship, however, remains an intriguing challenge. Herein we put forward a new hierarchical assembly strategy towards rational and precise construction of intricate single-crystal superstructures. Firstly, two unprecedented superclusters in Rubik's cube's form with a size of ≈2×2×2 nm³ are constructed by aggregation of eight {Pr₄ Sb₁₂ } oxohalide clusters as secondary building units (SBUs). Then, the Rubik's cubes further act as isolable tertiary building units (TBUs) to assemble diversified single-crystal superstructures. Importantly, intermediate assembly states are captured, which helps illustrate the evolution of TBU-based superstructures and thus provides a profound understanding of the assembly process of superstructures at the atomic level.

Heterotrimetallic Double Cavity Cages: Syntheses and Selective Guest Binding

A strategy for the generation of heterotrimetallic double cavity (DC) cages [Pdn Ptm L4 ]6+ (DC1: n=1, m=2; and DC2: n=2, m=1) is reported. The DC cages were generated by combining an inert platinum(II) tetrapyridylaldehyde complex with a suitably substituted pyridylamine and PdII ions. 1 H and DOSY nuclear magnetic resonance spectroscopy (NMR) and electrospray ionization mass spectrometry (ESIMS) data were consistent with the formation of the DC architectures. DC1 and DC2 were shown to interact with several different guest molecules. The structure of DC1, which features two identical cavities, binding two 2,6-diaminoanthraquinone (DAQ) guest molecules was determined by single-crystal X-ray crystallography. In addition, DC1 was shown to bind two molecules of 5-fluorouracil (5-FU) in a statistical (non-cooperative) manner. In contrast, DC2, which features two different cage cavities, was found to interact with two different guests, 5-FU and cisplatin, selectively.

Post-synthetic modifications of metal–organic cages

Metal-organic cages (MOCs) are discrete, supramolecular entities that consist of metal nodes and organic linkers, which can offer solution processability and high porosity. Thereby, their predesigned structures can undergo post-synthetic modifications (PSMs) to introduce new functional groups and properties by modifying the linker, metal node, pore or surface environment. This Review explores current PSM strategies used for MOCs, including covalent, coordination and noncovalent methods. The effects of newly introduced functional groups or generated complexes upon the PSMs of MOCs are also detailed, such as improving structural stability or endowing desired functionalities. The development of the aforementioned design principles has enabled systematic approaches for the development and characterization of families of MOCs and, thereby, provides insight into structure-function relationships that will guide future developments.

Fabrication of Multilayered Composite Nanofibers Using Continuous Chaotic Printing and Electrospinning: Chaotic Electrospinning

Multi-material and multilayered micro- and nanostructures are prominently featured in nature and engineering and are recognized by their remarkable properties. Unfortunately, the fabrication of micro- and nanostructured materials through conventional processes is challenging and costly. Herein, we introduce a high-throughput, continuous, and versatile strategy for the fabrication of polymer fibers with complex multilayered nanostructures. Chaotic electrospinning (ChE) is based on the coupling of continuous chaotic printing (CCP) and electrospinning, which produces fibers with an internal multi-material microstructure. When a CCP printhead is used as an electrospinning nozzle, the diameter of the fibers is further scaled down by 3 orders of magnitude while preserving their internal structure. ChE enables the use of various polymer inks for the creation of nanofibers with a customizable number of internal nanolayers. Our results showcase the versatility and tunability of ChE to fabricate multilayered structures at the nanoscale at high throughput. We apply ChE to the synthesis of unique carbon textile electrodes composed of nanofibers with striations carved into their surface at regular intervals. These striated carbon electrodes with high surface areas exhibit 3- to 4-fold increases in specific capacitance compared to regular carbon nanofibers; ChE holds great promise for the cost-effective fabrication of electrodes for supercapacitors and other applications.

Recent advances in heteroleptic multiple-stranded metallosupramolecules

Well-ordered combination of defined coordination spheres and multiple types of ligands (heteroleptic) in a given structure can expand the structural complexity and functional diversity of the resulting metallosupramolecules. Such heteroleptic metallosupramolecular architectures are expected to afford advanced utility in a variety of applications. In this concise review article, recent advances in the development of multi-nuclear-cluster-based heteroleptic multiple-stranded (HLMS) metallosupramolecules are summarized and demonstrated. To construct HLMS metallosupramolecules, one type of multitopic ligands can be employed for building up multiple strands, while another type of ligands can be utilized to construct multi-nuclear clusters. Most HLMS metallosupramolecules adopt helical geometries and have high molecular symmetry, which can be key factors for the structural completion. HLMS metallosupramolecules can be used as basic building blocks for the fabrication of higher-order polymeric or discrete assembly architectures with well-defined geometries.

"Eggs in egg cartons": co-crystallization to embed molecular cages into crystalline lattices

Discrete (M3L2) n cages assembled from a tripodal ligand (L) and metal ions (M: Cu(i) or Ag(i)) are embedded in networked coordination hosts formed by partial dissociation of the same discrete cages during the crystallization process. The resulting "eggs-in-an-egg-carton" structures provide unique examples of the co-crystallization of discrete and infinite coordination frameworks.

Coordinative helix–helix association of heteroleptic metallosupramolecular helicates

Coordinative helix–helix association of racemic metallosupramolecular helicates is controllably synthesized and fully characterized.

Metallosupramolecular Architectures of Ambivergent Bis(Amino Acid) Biphenyldiimides

The metallosupramolecular chemistry of two enantiopure dicarboxylate ligands has been explored for their potential to form discrete or polymeric interlocked motifs. Consequently, both discrete and polymeric supramolecular complexes have been synthesised, yielding M₂ L₂ metallomacrocycles (1 and 2), a heteroleptic M₂ L₃ metallomacrobicycle (3), a non-interpenetrated coordination polymer (4), and highly unusual chiral M₈ L₈ squares (5 and 6). There appears to be a preference for the ligands to form M₂ L₂ -type metallomacrocyclic structural units (which feature in 1-4), although these do not engage in any mechanical interlocking, which is perhaps a combined function of the ligand flexibility and relatively small pi-surface contrasted to previous analogues. Using copper paddlewheel SBUs, chiral double-walled squares (5 and 6) are formed with large internal cavities yet poor stabilities, unexpectedly featuring the paddlewheel motifs at the vertices of the polygonal complex.

Coordination [CoII2] and [CoIIZnII] Helicates Showing Slow Magnetic Relaxation

The slow magnetic relaxation of Co^II ions in the elusive intermediate geometry between the trigonal prism and antiprism has been studied on the new [Co₂L₃]⁴⁺ and [CoZnL₃]⁴⁺ coordination helicates [L is a bis(pyrazolylpyridine) ligand]. Solution paramagnetic ¹H NMR and solid-state magnetization measurements unveil single-molecule-magnet behavior with small axial anisotropy, as predicted previously.