Metal-organic Polyhedra Research Articles

Application of Crystalline Matrices for the Structural Determination of Organic Molecules.

While single-crystal X-ray diffraction (SC-XRD) is one of the most powerful structural determination techniques for organic molecules, the requirement of obtaining a suitable crystal for analysis limits its applicability, particularly for liquids and amorphous solids. The emergent use of preformed porous crystalline matrices that can absorb organic compounds and stabilize them via host–guest interactions for observation via SC-XRD offers a way to overcome this hindrance. A topical and current discussion of SC-XRD in organic chemistry and the use of preformed matrices for the in crystallo analysis of organic compounds, with a particular focus on the absolute structure determination of chiral molecules, is presented. Preformed crystalline matrices that are covered include metal–organic frameworks (MOFs) as used in the crystalline sponge method, metal–organic polyhedra (MOPs, coordination cages), porous organic materials (POMs)/porous organic molecular crystals (POMCs), and biological scaffolds. An outlook and perspective on the current technology and on its future directions is provided.

Multivariate Porous Platform Based on Metal-Organic Polyhedra with Controllable Functionality Assembly

Chemical environment of pores is important for various applications of porous solids. Thanks to reticular chemistry, metal-organic frameworks (MOFs) became a versatile platform targeting numerous applications through multiple functionalization. Although multivariate MOFs often display novel properties, identifying and manipulating pore types remain a daunting challenge. Here, we present an isoreticular series of Zr-based metal-organic polyhedra (MOPs) as a porous platform to achieve controllable intrinsic pores. Two multivariate synthetic approaches were demonstrated: a mixed-cage strategy where functionalized cages are mixed, compared to the conventional mixed-linker strategy, which yields a random distribution of functionalities. A remarkable difference in functionality assembly was achieved between the strategies with complexity increasing from binary to senary systems. More interestingly, distinct photophysical properties were observed between mixed-linker and mixed-cage samples attributed to radiative decay kinetics. This study highlights the potential of MOPs as a unique multivariate porous platform with tunable component assembly to study the emerging properties of multivariate porous solids.

Synthesis of Polycarboxylate Rhodium(II) Metal–Organic Polyhedra (MOPs) and their use as Building Blocks for Highly Connected Metal–Organic Frameworks (MOFs)

AbstractUse of preformed metal‐organic polyhedra (MOPs) as supermolecular building blocks (SBBs) for the synthesis of metal‐organic frameworks (MOFs) remains underexplored due to lack of robust functionalized MOPs. Herein we report the use of polycarboxylate cuboctahedral RhII‐MOPs for constructing highly‐connected MOFs. Cuboctahedral MOPs were functionalized with carboxylic acid groups on their 12 vertices or 24 edges through coordinative or covalent post‐synthetic routes, respectively. We then used each isolated polycarboxylate RhII‐MOP as 12‐c cuboctahedral or 24‐c rhombicuboctahedral SBBs that, upon linkage with metallic secondary building units (SBUs), afford bimetallic highly‐connected MOFs. The assembly of a pre‐synthesized 12‐c SBB with a 4‐c paddle‐wheel SBU, and a 24‐c SBB with a 3‐c triangular CuII SBU gave rise to bimetallic MOFs having ftw (4,12)‐c or rht (3,24)‐c topologies, respectively.

Synthesis of Polycarboxylate Rhodium(II) Metal-Organic Polyhedra (MOPs) and their use as Building Blocks for Highly Connected Metal-Organic Frameworks (MOFs).

Use of preformed metal-organic polyhedra (MOPs) as supermolecular building blocks (SBBs) for the synthesis of metal-organic frameworks (MOFs) remains underexplored due to lack of robust functionalized MOPs. Herein we report the use of polycarboxylate cuboctahedral RhII -MOPs for constructing highly-connected MOFs. Cuboctahedral MOPs were functionalized with carboxylic acid groups on their 12 vertices or 24 edges through coordinative or covalent post-synthetic routes, respectively. We then used each isolated polycarboxylate RhII -MOP as 12-c cuboctahedral or 24-c rhombicuboctahedral SBBs that, upon linkage with metallic secondary building units (SBUs), afford bimetallic highly-connected MOFs. The assembly of a pre-synthesized 12-c SBB with a 4-c paddle-wheel SBU, and a 24-c SBB with a 3-c triangular CuII SBU gave rise to bimetallic MOFs having ftw (4,12)-c or rht (3,24)-c topologies, respectively.

Unexpected Elasticity in Assemblies of Glassy Supra-Nanoparticle Clusters.

Granular materials, composed of densely packed particles, are known to possess unique mechanical properties that are highly dependent on the surface structure of the particles. A microscopic understanding of the structure-property relationship in these systems remains unclear. Here, supra-nanoparticle clusters (SNPCs) with precise structures are developed as model systems to elucidate the unexpected elastic behaviors. SNPCs are prepared by coordination-driven assembly of polyhedral oligomeric silsesquioxane (POSS) with metal-organic polyhedron (MOP). Due to the disparity in sizes, the POSS-MOP assemblies, like their classic nanoparticles counterparts, ordering is suppressed, and the POSS-MOP mixtures will vitrify or jam as a function of decreasing temperature. An unexpected elasticity is observed for the SNPC assemblies with a high modulus that is maintained at temperatures far beyond the glass transition temperature. From studies on the dynamics of the hierarchical structures of SNPCs and molecular dynamic simulation, the elasticity has its origins in the interpenetration of POSS-ended arms. The physical molecular interpenetration and inter-locking phenomenon favors the convenient solution or pressing processing of the novel cluster-based elastomers.

Unexpected Elasticity in Assemblies of Glassy Supra‐Nanoparticle Clusters

AbstractGranular materials, composed of densely packed particles, are known to possess unique mechanical properties that are highly dependent on the surface structure of the particles. A microscopic understanding of the structure‐property relationship in these systems remains unclear. Here, supra‐nanoparticle clusters (SNPCs) with precise structures are developed as model systems to elucidate the unexpected elastic behaviors. SNPCs are prepared by coordination‐driven assembly of polyhedral oligomeric silsesquioxane (POSS) with metal‐organic polyhedron (MOP). Due to the disparity in sizes, the POSS‐MOP assemblies, like their classic nanoparticles counterparts, ordering is suppressed, and the POSS‐MOP mixtures will vitrify or jam as a function of decreasing temperature. An unexpected elasticity is observed for the SNPC assemblies with a high modulus that is maintained at temperatures far beyond the glass transition temperature. From studies on the dynamics of the hierarchical structures of SNPCs and molecular dynamic simulation, the elasticity has its origins in the interpenetration of POSS‐ended arms. The physical molecular interpenetration and inter‐locking phenomenon favors the convenient solution or pressing processing of the novel cluster‐based elastomers.

The rise of metal-organic polyhedra.

Metal-organic polyhedra are a member of metal-organic materials, and are together with metal-organic frameworks utilized as emerging porous platforms for numerous applications in energy- and bio-related sciences. However, metal-organic polyhedra have been significantly underexplored, unlike their metal-organic framework counterparts. In this review, we will cover the topologies and the classification of metal-organic polyhedra and share several suggestions, which might be useful to synthetic chemists regarding the future directions in this rapid-growing field.

Crystalline assembly of metal-organic polyhedra driven by ionic interactions with polyoxometalates.

Charge-driven self-assembly of cationic zirconium-based metal-organic polyhedra (MOPs) with polyoxometalates (POMs) leads to a series of porous crystalline salts, prepared by simple mixing of soluble precursors. The reactivity of immobilized POMs was greatly increased, as demonstrated by their fast reduction by hydrazine vapors, without loss of structural integrity.

Microwave-Assisted Synthesis of Water-Stable Zirconium Metal-Organic Polyhedron: Serving as Efficient Visible-Light Photocatalyst for Cr(Vi) Reduction

Microwave-Assisted Synthesis of Water-Stable Zirconium Metal-Organic Polyhedron: Serving as Efficient Visible-Light Photocatalyst for Cr(Vi) Reduction

Topological Strain-Induced Regioselective Linker Elimination in a Chiral Zr(IV)-Based Metal-Organic Framework

Summary Zr-carboxylate metal-organic frameworks (MOFs) are structurally robust materials, in part due to their strong coordination bonds. The regioselective Zr–O bond cleavage and formation between 3D architectures are thus challenging and are heretofore unexplored. In this work, by introducing highly flexible 18-crown-6-ether functionalities into a homochiral Zr-MOF, we report an unprecedented topology transition in which a 4,10-connected framework undergoes a rapid solid-state transition into a thermodynamically more stable 4,8-connected analog by a regioselective-linker-elimination under ambient conditions. The transition process was unambiguously unraveled by single-crystal and powder X-ray diffraction studies, and we proposed a possible transition mechanism based on various control experiments and theoretical calculations. The excellent chemical stability and substantially expanded porosity and pore apertures endowed the transformed chiral MOF with an exceptional capacity for the enantioadsorptive and solid-phase extractive separation of the racemic drug molecule of lansoprazole with 98% ee and 93% ee, respectively.

Synthesis, crystal structure and iodine capture of Zr-based metal-organic polyhedron

A new zirconium-based metal-organic polyhedron (Zr-MOP-1) was successfully synthesized from Bis(cyclopentadienyl)zirconium dichloride and 2,5-pyridinedicarboxylic acid under solvothermal condition. It was characterized by single-crystal X-ray diffraction, powder X-ray diffraction, thermogravimetric analysis and infrared spectroscopy. Four trinuclear zirconocene building blocks as well as six linear carboxylate ligands give rise to its tetrahedral configuration. Interestingly, Zr-MOP-1 possesses considerable reversible iodine sorption performance in organic phase featuring an optimal adsorption capacity of 283 mg g−1. The related kinetics absorption and desorption process were fully explored in detail by multiple complementary experiments and the adsorbed iodine species (I− and I3−) in Zr-MOP-1 had been further identified through crystallographic analyses. This work provides new possibilities for developing new and functional zirconium-based molecular cages materials.

Porous Metal-Organic Polyhedra: Morphology, Porosity, and Guest Binding.

Designing porous materials which can selectively adsorb CO2 or CH4 is an important environmental and industrial goal which requires an understanding of the host–guest interactions involved at the atomic scale. Metal–organic polyhedra (MOPs) showing permanent porosity upon desolvation are rarely observed. We report a family of MOPs (Cu-1a, Cu-1b, Cu-2), which derive their permanent porosity from cavities between packed cages rather than from within the polyhedra. Thus, for Cu-1a, the void fraction outside the cages totals 56% with only 2% within. The relative stabilities of these MOP structures are rationalized by considering their weak nondirectional packing interactions using Hirshfeld surface analyses. The exceptional stability of Cu-1a enables a detailed structural investigation into the adsorption of CO2 and CH4 using in situ X-ray and neutron diffraction, coupled with DFT calculations. The primary binding sites for adsorbed CO2 and CH4 in Cu-1a are found to be the open metal sites and pockets defined by the faces of phenyl rings. More importantly, the structural analysis of a hydrated sample of Cu-1a reveals a strong hydrogen bond between the adsorbed CO2 molecule and the Cu(II)-bound water molecule, shedding light on previous empirical and theoretical observations that partial hydration of metal−organic framework (MOF) materials containing open metal sites increases their uptake of CO2. The results of the crystallographic study on MOP–gas binding have been rationalized using DFT calculations, yielding individual binding energies for the various pore environments of Cu-1a.

Two-Step Synthesis of Linear and Bent Dicarboxylic Acid Metalloligands with Lengths of up to 3 nm.

Nanometer-sized polycarboxylate ligands are interesting building blocks for metallasupramolecular chemistry, but access to these compounds is often limited by complicated synthetic pathways. Here, we describe a simple two-step protocol, which allows preparing linear and bent dicarboxylate ligands with lengths of up to 3 nm from commercially available compounds. The ligands are prepared by iron-templated polycondensation reactions involving arylboronic acids and nioxime. The final products contain two iron clathrochelate complexes and two terminal carboxyphenylene groups. To demonstrate that the new ligands are suitable for the construction of more complex molecular nanostructures, we have prepared a Cu-based metal-organic polyhedron, which represents the largest M4L4 cage described so far.

Breathing Metal–Organic Polyhedra Controlled by Light for Carbon Dioxide Capture and Liberation

Metal–organic polyhedra (MOPs) have emerged as versatile platforms for artificial models of biological systems due to their discrete structure and modular nature. However, the design and fabricatio...

Nanotrap Grafted Anion Exchangeable Hybrid Materials for Efficient Removal of Toxic Oxoanions from Water.

Water pollution has attracted worldwide significant attention ever since the finding of its harmful effects on the whole ecosystem, including human health. Although several materials are known for selective removal of specific contaminants, designing a single material that can adsorb a variety of water contaminants is still a very challenging task due to a lack of proper design strategies. Herein, we have rationally designed a new class of anion exchangeable hybrid material where the nanosized cationic metal–organic polyhedra (MOP) are embedded inside a porous covalent organic framework (COF) with specific binding sites for toxic oxoanions. The resulting hybrid material exhibits very fast and selective sequestration of high as well as trace amount of a wide range of toxic oxoanions (HAsO42–, SeO42–, CrO42–, ReO4–, and MnO4–) from the mixture of excessive (∼1000-fold) other interfering anions to well below the permissible drinking water limit. Moreover, the hybrid cationic nanotrap material can reduce the As(V) level from a highly contaminated groundwater sample to below the WHO permitted level.

Confinement Effect on the Surface of a Metal–Organic Polyhedron: Tunable Thermoresponsiveness and Water Permeability

Materials under space confinement can alter their physical and chemical properties, paving the way for new science and novel applications. Nanoparticles can enforce spatial constraints on the polym...

Self-Assembly of Imidazolium-Functionalized Zr-Based Metal-Organic Polyhedra for Catalytic Conversion of CO2 into Cyclic Carbonates.

Three cationic capsule-shaped Zr-based metal-organic polyhedra (MOPs) with different cavity sizes were successfully constructed through the self-assembly of trinuclear zirconocene clusters and imidazolium-functionalized dicarboxylic ligands. Owing to the imidazolium groups in the MOPs, they show good CO2 adsorption uptake. Moreover, the halogen anions of the imidazolium groups and Brønsted acid sites (-OH) in the Zr-based knots are in close proximity, making these MOPs able to catalyze synergistically the cycloaddition reaction of CO2 with epoxides into cyclic carbonates. This is the first report of using MOPs as catalysts for this reaction without the addition of a cocatalyst.

Solvated and Deformed Hairy Metal–Organic Polyhedron

Despite numerous studies have been conducted to explore the crystalline structures of various metal-organic polyhedra (MOPs), the direct probing of solvated and deformed structures of MOPs is still...

Rh(II)-based Metal–Organic Polyhedra

Metal–organic polyhedra (MOPs) are discrete porous materials which feature intriguing structures, well-defined cavities, and emergent functions. Among them, the recently developed Rh(II)-based MOPs...

Shaping Microcrystals of Metal-Organic Frameworks by Reaction-Diffusion.

When components of a metal-organic framework (MOF) and a crystal growth modulator diffuse through a gel medium, they can form arrays of regularly-spaced precipitation bands containing MOF crystals of different morphologies. With time, slow variations in the local concentrations of the growth modulator cause the crystals to change their shapes, ultimately resulting in unusual concave microcrystallites not available via solution-based methods. The reaction-diffusion and periodic precipitation phenomena 1) extend to various types of MOFs and also MOPs (metal-organic polyhedra), and 2) can be multiplexed to realize within one gel multiple growth conditions, in effect leading to various crystalline phases or polycrystalline formations.