Hierarchical 2D honeycomb-like network from barium-seamed nanocapsules

We report on a two-dimensional hexagonal "honeycomb" network comprising barium-seamed metal-organic nanocapsules involving a hexameric assembly of pyrogallol[4]arene ligands. The incorporated barium ions act as spacers to generate a solvent-accessible void, hierarchical self-assembly having an individual void volume near 13 000 Å3. This work illustrates the surprising chemistry that remains to be discovered by integrating large or classically non-reactive metal ions within supramolecular assemblies, networks, and organic nanocapsules.

Redox-Controlled Self-Assembly of Vanadium-Seamed Hexameric Pyrogallol[4]Arene Nanocapsules

Here we report the controlled self-assembly of vanadium-seamed metal-organic nanocapsules with specific metal oxidation state distributions. Three supramolecular assemblies composed of the same numbers of components including 24 metal centers and six pyrogallol[4]arene ligands were constructed: a VIII24L6 capsule, a mixed-valence VIII18VIV6L6 capsule, and a VIV24L6 capsule. Crystallographic studies of the new capsules reveal their remarkable structural complexity and geometries, while marked differences in metal oxidation state distribution greatly affect the photoelectric conversion properties of these assemblies. This work therefore represents a significant step forward in the construction of intricate metal-organic architectures with tailored structure and functionality.

Nanocapsules of unprecedented internal volume seamed by calcium ions

The inception of an unprecedented class of voluminous Platonic solids displaying hierarchical geometry based on pyrogallol[4]arene moieties seamed by divalent calcium ion is described. Single-crystal X-ray structural determination has established the highly conserved geometry of two original Ca2+-seamed nanocapsules to be essentially cubic in shape with C-ethylpyrogallol[4]arene units located along the twelve edges of the cube which are then bridged by metallic polyatomic cations ([Ca4Cl]7+ or [Ca(HCO2)Na4]5+) at the six cube faces. The accessible volume of the nanocapsules is ca. 3500 Å3 and 2500 Å3 and is completely isolated from the exterior of the capsules. These remarkable nanocapsule discoveries cast a spotlight on a marginalized area of synthetic materials chemistry and encourage future exploration of diversiform supramolecular assemblies, networks, and capsules built on calcium, with clear benefits deriving from the intrinsic biocompatibility of calcium. Finally, a proof-of-concept is demonstrated for fluorescent reporter encapsulation and sustained release from the calcium-seamed nanocapsules, suggesting their potential as delivery vehicles for drugs, nutrients, preservatives, or antioxidants.

A copper-seamed coordination nanocapsule as a semiconductor photocatalyst for molecular oxygen activation

Here we report that a Cu²⁺-seamed coordination nanocapsule can serve as an efficient semiconductor photocatalyst for molecular oxygen activation. This capsule was constructed through a redox reaction facilitated self-assembly of cuprous bromide and C-pentyl-pyrogallol[4]arene. Photophysical and electrochemical studies revealed its strong visible-light absorption and photocurrent polarity switching effect. This novel molecular solid material is capable of activating molecular oxygen into reactive oxygen species under simulated sunlight irradiation. The oxygen activation process has been exploited for catalyzing aerobic oxidation reactions. The present work provides new insights into designing nonporous discrete metal-organic supramolecular assemblies for solar-driven molecular oxygen activation.

Solution‐Phase Magnetic Mechanistic Study of Ni‐Seamed Pyrogallol[4]arene Nanocapsules Reveal Presence of Novel Cylindrical and Spherical Species

The magnetic properties of nickel‐seamed C‐pyrogallol[4]arene (PgC₃Ni) hexamers and dimers are studied for the first time in solution. The combination of small‐angle neutron scattering and superconducting quantum interference device magnetometer measurements of the solution species reveal their paramagnetic and weakly antiferromagnetic behaviour. Surprisingly, the magnetic results indicated the presence of an unprecedented 13 Å‐radius species, larger than both the dimeric and hexameric nanocapsules with both octahedral and square‐planar metal centers. To confirm the presence of this novel species, we performed a mechanistic study of PgC₃Ni as a function of temperature and solvent and deduced the presence of two additional new species: a) an 11 Å cylinder with Ni atoms seaming the tubular framework and b) an 8 Å‐radius sphere with non‐interacting Ni centers located within the internal cavity. Select parameters that shift the equilibrium towards desired species are also identified.

Coordination Polymers Constructed from Pyrogallol[4]arene-Assembled Metal-Organic Nanocapsules

Coordination polymers, commonly known as infinite crystalline lattices, are versatile networks and have diverse potential applications in the fields of gas storage, molecular separation, catalysis, optics, and drug delivery, among other areas. Secondary building blocks, mainly incorporating rigid polydentate organic linkers and metal ions or clusters, are commonly employed to construct coordination polymers. Recently, novel building blocks such as coordination polyhedra have been utilized as metal nodes to fabricate coordination polymers. Benefiting from the rigid porous structure of the coordination polyhedron, prefabricated designer "pores" can be incorporated in this type of coordinate polymer. In this Account, coordination polymers built by pyrogallol[4]arene-assembled metal-organic nanocapsules are summarized. This class of metal-organic nanocapsule possesses the following advantages that make them excellent candidates in the construction of coordination polymers: (i) Various geometrical shapes with different volumes of the inner cavities can be obtained from these capsules. Among them, the two main categories illustrated are dimeric and hexameric capsules, which comprise two and six pyrogallol[4]arenes units, respectively. (ii) A wide range of possible metal ions ranging from main group metals to transition metals and even lanthanides have been demonstrated to seam the capsules. Therefore, these coordination polymers can be endowed with fascinating functionalities such as magnetism, semiconductivity, luminescence, and radioactivity. (iii) Up to 24 metal ions have been successfully embedded on the surface of the nanocapsule, each a potential reaction site in the construction of coordination polymers, opening up pathways for the formation of multidimensional frameworks.In this Account, we focus primarily on the synthesis and the structural information on pyrogallol[4]arene-derived coordination polymers. Coordination polymers can be formed by introducing linkers with two coordination sites, using pyrogallol[4]arenes with coordination sites on the tail, or even via metal ions cross-linking with each other. Machine learning was recently developed to help us predict and screen the structures of the coordination polymers. With single crystal analysis in hand, detailed structural information provides a molecular-level perspective. Significantly, following the formation of coordination polymers, the overall shape and structure of the discrete metal-organic nanocapsules remains essentially unchanged, with full retention of the prefabricated pores. If a rigid linker is used to connect capsules, more than one lattice void with different volumes can be found within the framework. Thus, molecules with different sizes could potentially be encapsulated within these coordination polymers. In addition, flexible ligands can also be employed as linkers. For example, polymers have been employed as large linkers that transform the crystalline coordination polymers into polymer matrices, paving the way toward the synthesis of advanced functional materials. Overall, coordination polymers constructed with pyrogallol[4]arene-assembled metal-organic nanocapsules show wide diversity and tunability in structure and fascinating properties, as well as the promise of built-in functionality in the future.

Solution structure of zinc-seamed C-alkylpyrogallol[4]arene dimeric nanocapsules

The structural stability and solution geometry of zinc-seamed-C-propylpyrogallol[4]arene dimers has been studied in solution using in situ neutron scattering and 2D-DOSY NMR methods. In comparison with the structures of the analogous copper-/nickel-seamed dimeric entities, the spherical geometry of the PgC₃Zn species (R = 9.4 Å; diffusion coefficient = 1.05 × 10^-10 m² s^-1) is larger due to the presence of ligands at the periphery in solution. This enhanced radius in solution due to ligation is also consistent with the findings of model molecular dynamics simulations of the zinc-seamed dimers.

Controlled hierarchical self-assembly of networked coordination nanocapsules via the use of molecular chaperones

Supramolecular chaperones play an important role in directing the assembly of multiple protein subunits and redox-active metal ions into precise, complex and functional quaternary structures. Here we report that hydroxyl tailed C-alkylpyrogallol[4]arene ligands and redox-active MnII ions, with the assistance of proline chaperone molecules, can assemble into two-dimensional (2D) and/or three-dimensional (3D) networked nanocapsules. Dimensionality is controlled by coordination between the exterior of nanocapsule subunits, and endohedral functionalization within the 2D system is achieved via chaperone guest encapsulation. The tailoring of surface properties of nanocapsules via coordination chemistry is also shown as an effective method for the fine-tuning magnetic properties, and electrochemical and spectroscopic studies support that the nanocapsule is an effective homogeneous water-oxidation electrocatalyst, operating at pH 6.07 with an exceptionally low overpotential of 368 mV.

Novel keto-enol tautomerism in 1,3,5-trihydroxybenzene systems

We report a new synthesis of the water-soluble compound 1,3,5-trihydroxy-2,4,6-trimethylsulfonic acid (1), which exists in two tautomeric forms (60 : 40::enol%:keto%) and can be used as a proton conductor. Quantum chemical calculations show the importance of intramolecular hydrogen bonding and the presence of implicit MeOH solvent on the relative stabilities of the tautomers. 1 complexes with lanthanides through its sulfonato groups and forms a layered cage-like structure with one intramolecular and two intermolecular hydrogen bonds.

Borohydride stabilized gold-silver bimetallic nanocatalysts for highly efficient 4-nitrophenol reduction

Bimetallic Au _x Ag_1-x nanoparticles, prepared using sodium borohydride as the sole reducing and capping agent for various NaBH₄ : metal molar ratios, were investigated as catalysts for 4-nitrophenol reduction. This approach yielded the highest catalytic activities observed for this model reaction to date.

Facile, one-pot, in aqua synthesis of catalytically competent gold nanoparticles using pyrogallol[4]arene as the sole reagent

Rapid and facile synthesis of macrocycle-capped gold nanoparticles employing pyrogallol[4]arenes as a dual-role reducing and stabilizing agent.

Phase dependent structural perturbation of a robust multicomponent assembled icosahedral array

We report on the assembly of three-fold axially compressed icosahedral arrays of the bowl shaped p-sulfonatocalix[4]arene molecules in the solid-state, intricately bound to dipicolinate and yttrium(iii) ions, with the compression reflected in Hirshfeld surface analyses. Solution studies show dissolution of the icosahedra intact, but with a geometrical rearrangement to regular icosahedra.

Formation of Water Channels in the Crystalline Hydrates of Macrocyclic Compounds

Crystalline hydrates of macrocyclic compounds such as pyroagllol[4]arenes (PgCs) and resorcin[4]arenes (RsCs) are rare owing to their lower water solubility. Functionalization of these macrocyclic compounds is an affordable way to enhance water solubility. However, functionalization also encounters the formation of multiple conformers and subsequent difficulty in purification of the product. Herein, four novel crystalline hydrates of functionalized PgCs and RsCs were synthesized. Formation of water channels and the effects of intermolecular interactions on the physical properties of these novel hydrates are discussed.

Ionothermal synthesis of magnetically-retrievable mesoporous carbons from alkyne-appended ionic liquids and demonstration of their use in selective dye removal

Tailored metal-containing ionic liquids generate porous carbon suitable for selective dye sorption and Fenton chemistry by thermal cyclotrimerization of terminal alkynes.

A M18L6 metal–organic nanocapsule with open windows using mixed macrocycles

Introducing defects into metal–organic nanocapsules creates two open windows.

On the non-innocence of the imidazolium cation in a rapid microwave synthesis of oleylamine-capped gold nanoparticles in an ionic liquid

We report a very fast (10–30 s) microwave method to prepare oleylamine-capped, monodisperse ca. 8–11 nm gold nanoparticles in an ionic liquid

Preparation of Magnesium-Seamed C-Alkylpyrogallol[4]arene Nanocapsules with Varying Chain Lengths

Novel supramolecular nanocapsules based on metal-directed assembly have captured tremendous interest due to their applications in fields such as catalysis, selective gas adsorption, and biomedicine. Functionalization of metal-organic nanocapsules (MONCs) by using organic ligands with different pendant groups affords more complexity to the structure and may lead to novel properties. In this work, we report the solvothermal synthesis of a group of magnesium-based MONCs using C-alkylpyrogallol[4]arenes with varying alkyl chain lengths. The structures of these nanocapsules are characterized by single-crystal X-ray diffraction analysis. As expected, a progression in size of the nanocapsules is observed as the alkyl chain length increases. The effect of the chain length on the solubility of MONCs in water has been determined. This work shows the generality of the solvothermal approach for the synthesis of MONCs with different organic ligands and demonstrates that surface functionalization of MONCs may serve as an effective way to tailor their properties. The unique biocompatible nature and inherent large cavity of these magnesium-based MONCs make these nanocapsules promising for potential applications in biomedicine.

Self-assembly of M7L2 metal–organic nanocapsules using mixed macrocycles

The solvothermal synthesis of two M₇L₂ metal–organic nanocapsules from C-alkyl pyrogallol[3]resorcin[1]arene is reported.

Self-assembly of magnesium-seamed hexameric pyrogallol[4]arene nanocapsules

The magnesium-seamed hexameric pyrogallol[4]arene nanocapsule and its cocrystallization with pyridine molecules are presented.

Novel magnesium-seamed organic nanocapsules with hierarchical structural complexity

Novel magnesium-seamed organic nanocapsules with hierarchical structural complexity are prepared via endohedral and exterior functionalization.

Process Development for Separation of Conformers from Derivatives of Resorcin[4]arenes and Pyrogallol[4]arenes

Macrocyclic compounds, such as resorcin[4]arenes and pyrogallol[4]arenes, have proven to be useful building blocks in the construction of supramolecular organic frameworks (SOFs) because of their unique bowl-like shape and ability to interact through variety of intermolecular interactions. Herein, we report the synthesis and crystal structures of two functionalized resorcin[4]arenes and pyroagllol[4]arenes, 4-hydroxyphenylresorcin[4]arenes, and 4-hydroxyphenylpyrogallol[4]arenes. These phenyl-functionalized macrocycles usually have different conformers, such as cone, boat, chair, saddle, and diamond. The successful separation of predominant conformers from the crude product was carried out with solvent-extraction technique. The shape and molecular arrangement of these conformers in the individual crystal structure was verified with single-crystal X-ray diffraction studies.

Fluid dynamic lateral slicing of high tensile strength carbon nanotubes

Lateral slicing of micron length carbon nanotubes (CNTs) is effective on laser irradiation of the materials suspended within dynamic liquid thin films in a microfluidic vortex fluidic device (VFD). The method produces sliced CNTs with minimal defects in the absence of any chemical stabilizers, having broad length distributions centred at ca 190, 160 nm and 171 nm for single, double and multi walled CNTs respectively, as established using atomic force microscopy and supported by small angle neutron scattering solution data. Molecular dynamics simulations on a bent single walled carbon nanotube (SWCNT) with a radius of curvature of order 10 nm results in tearing across the tube upon heating, highlighting the role of shear forces which bend the tube forming strained bonds which are ruptured by the laser irradiation. CNT slicing occurs with the VFD operating in both the confined mode for a finite volume of liquid and continuous flow for scalability purposes.

Syntheses and characterization of aryl-substituted pyrogallol[4]arenes and resorcin[4]arenes

Thirteen aryl-substituted pyrogallol[4]arene and resorcin[4]arenes structures are synthesized and characterized. The effect of the varying aryl pendent groups on π–π distance, the inward tilt of the pendent –R groups, the twist angle of the pendent –R groups, and the angle between the pendent –R groups is methodically investigated and discussed.