Unravelling the Growth of Supramolecular Metal–Organic Frameworks Based on Metal-Nucleobase Entities (original) (raw)
Related papers
Crystal Growth & Design, 2014
The present work assesses the ability of [Cu 2 (μ-adenine) 4 (X) 2 ] 2+ and [Cu 2 (μ-adenine) 2 (μ-X) 2 (X) 2 ] (X: Cl − or Br − ) metal-nucleobase dinuclear entities to build up supramolecular metal−organic frameworks (SupraMOFs) based on the complementary hydrogen bonding interactions established by the Watson−Crick and Hoogsteen faces of adjacent adenine moieties. The noncoplanar disposition of these synthons in the [Cu 2 (μ-adenine) 4 (X) 2 ] 2+ building unit leads to an open framework with one-dimensional (1D) channels of ca. 6 Å in compounds [Cu 2 (μ-adenine) 4 (Cl) 2 ]-Cl2·∼2MeOH (1, SMOF-1) and [Cu 2 (μ-adenine) 4 (Br) 2 ]-Br 2 ·∼2 MeOH (2, SMOF-2) sustained through the hydrogen bonding base pairing interactions among the Watson−Crick faces. In the case of the second building unit, [Cu 2 (μ-adenine) 2 (μ-X) 2 (X) 2 ], the coplanar arrangement of the two adenines in the dimeric unit does not allow a three-dimensional (3D) supramolecular architecture based only on the complementary hydrogen bonding interactions between the nucleobases. Therefore, other supramolecular interactions involving the halide ions and solvent molecules are crucial for determining the features of the crystal packing. In compound [Cu 2 (μ-adenine) 2 (μ-Cl) 2 (Cl) 2 ]·2MeOH (3, SMOF-3), base pairing interactions between adjacent adenines produce 1D supramolecular ribbons of dinuclear entities. These ribbons establish additional hydrogen bonds between the Hoogsteen face and the chloride anions of adjacent ribbons that are also reinforced by the presence of π−π stacking interactions among the adenines leading to a rigid synthon that gives rise to a robust 3D skeleton with the presence of micropores occupied by solvent molecules. In the case of the bromide analogue, the weaker hydrogen acceptor capacity of the bromide allows the solvent molecules to disrupt the self-assembly process of the dinuclear entities and prevents the formation of an open-framework supramolecular structure leading to the nonporous [Cu 2 (μadenine) 2 (μ-Br) 2 (Br) 2 ]·2PrOH (4) compound. According to gas adsorption studies, SMOF-1, SMOF-2, and SMOF-3 present a surface instability that creates a diffusion barrier that can be permeated only by strong interacting adsorbate molecules with high kinetic energy such as CO 2 but not N 2 , H 2 , and CH 4 . This feature makes them attractive for selective gas adsorption and separation technologies.
Supramolecular Chemistry in Solid State Materials such as Metal-Organic Frameworks
Israel Journal of Chemistry
Supramolecular chemistry has enriched the scientific research for more than fifty years reaching one of its summits in 2016, when the Chemistry Nobel Prize was awarded for the design and synthesis of molecular machines, in which host-guest chemistry plays a fundamental role. Recently, the groups of Omar Yaghi and Fraser Stoddart, among others, have demonstrated that this chemistry can be extended to the pores of metal-organic frameworks (MOFs). This heterogenization of supramolecular chemistry can be achieved through the incorporation of macrocycles to the organic struts of these highly porous and crystalline materials. Throughout this short review we summarize interesting examples of selective recognition by naturally occurring and synthetic macrocycles in solution and solid state; and later we survey important milestones to achieve specific recognition sites and develop host-guest chemistry at the pores of MOFs. This summary contains examples of different synthetic strategies to incorporate macrocycles to solid state materials, and in particular, to prepare supramolecular MOFs with particular properties and related applications. Specifically, the revised research includes the incorporation of both naturally occurring and synthetic macrocycles to solid state materials such as polymers, metal nanoparticles, etc., as prelude of the solid phase recognition studied in MOFs. An important number of the contributions presented here feature porous solids with smooth access to the host's cavity incorporated in the pores, allowing specific recognition of guest molecules. This smooth access to those active recognition sites in materials with extremely high surface area such as MOFs, open the possibility to develop the next generation of frontier materials with application in fields such as selective capture of water toxins and heterogeneous catalysis, among others.
2012
Metal-organic frameworks (MOFs) are newly emerging porous materials that feature well-defined crystal structures. [1] Owing to their high specific surface areas, tunable structures and functionalities, they have been extensively studied for applications in the areas of gas storage and separation, particularly for hydrogen, methane, and carbon dioxide. In general, MOF structures may be viewed as having two main components: the organic linker and the inorganic metal cluster (also known as secondary building unit, SBU). It is well-established that the combination of both components governs the final framework topology, which in turn determines the performance as a storage or separation medium. The dinuclear paddle-wheel cluster, a square building unit, is one of the commonly used SBUs in the isoreticular synthesis of MOFs owing to its ability to form innumerous structures with a large range of organic ligands. We are particularly interested in the dicopper(II) paddle-wheel cluster because of its enhanced moisture resistance over the Zn 4 O cluster and genesis of exposed metal sites after the removal of axially coordinated solvent molecules. The presence of open metal sites in the framework facilitates H 2 storage owing to the strong metal-H 2 interaction. Ideally, the method to maximize surface area is to use long, slim organic linkers. However, elongation of organic ligands often yields fragile or interpenetrated frameworks, which generally have a negative impact on gas-uptake capacity. To design and construct non-interpenetrated MOFs, one powerful strategy is utilizing metal-organic polyhedra (MOPs) as supermolecular building blocks (SBBs). Fur-thermore, a strategy employing dendritic ligands could possibly render MOFs with tolerance to slim organic linkers because of high connectivity. For example, the MOF assembled with 3-connected bte (for the definition see reference [7]) and dicopper(II) paddle-wheel cluster collapsed upon removal of guest solvents; however, a robust MOF (PCN-61, PCN stands for porous coordination network with permanent porosity) was obtained when 6-connected btei [7] (having the same core structure as bte) was used instead. Moreover, by stepwise extension of the ligands from btei to the almost doubly-expanded ttei, [7] a family of highly porous and robust MOFs (PCN-6X) with cuboctahedral cages as the SBBs was obtained. It is noteworthy to mention that members of the PCN-6X family exhibit exceptionally high surface areas and gas-uptake capacities with no interpenetration observed, even in the ttei case. [9] This systematic study of the extension of dendritic ligands emphasized the positive correlation between ligand connectivity and framework stability.
Hierarchical Self-Assembly of a Chiral Metal-Organic Framework Displaying Pronounced Porosity
Angewandte Chemie International Edition, 2010
Significant recent attention has been devoted to the development of useful self-assembled hybrid materials. [1] This is particularly the case for metal-organic frameworks (MOFs), which display properties such as regularity, porosity, robustness, and high surface area that lead to potential applications in areas such as catalysis, gas separation, and storage. [2, Our research groups and others have been developing new methods for the synthesis of both discrete and extended metal-organic materials, with particular interest in the controlled generation of increased structural complexity. [4] Herein we report a hierarchical self-assembly strategy which has been used to synthesize a new metal-organic framework. This strategy differs from the commonly employed molecular building block (MBB) and secondary building unit (SBU) approaches, where single metal ions or small inorganic clusters (polyhedra) are linked by bridging (often carboxylate) ligands in a one-pot reaction. In these approaches, substantial pore volume is achieved principally through the enthalpically favorable formation of an open framework overcoming the entropic penalties associated with the entrapment of solvent guest molecules. Kinetic control over the formation of the framework is achieved largely through the trial-and-error optimization of synthetic conditions to prevent formation of unwanted kinetic intermediates. In the hierarchical approach used here we have employed a series of distinct self-assembly steps, which operate across different levels of complexity, to incorporate predesigned, kinetically stable, discrete neutral supramolecular components into a metal-organic framework. In this way we show that it is possible to transcribe the properties of the discrete subcomponent into those of the framework product. This method involves the initial design and assembly of a discrete two-dimensional (2D) void-containing tecton containing unsaturated metal centers, followed by linkage of these sites with a bridging group in such a way that it is possible to transform the 2D voids in the subcomponent into 3D voids in a framework material. By using this approach we have generated a new neutral chiral MOF that displays significant porosity and gas-sorption behavior, and hence demonstrate that the host-guest properties of our discrete building blocks can be successfully imparted to the final MOF.
IUCrJ, 2018
In order to develop transferable and practical avenues for the assembly of coordination complexes into architectures with specific dimensionality, a strategy utilizing ligands capable of simultaneous metal coordination and self-complementary hydrogen bonding is presented. The three ligands used, 2(1H)-pyrazinone, 4(3H)-pyrimidinone and 4(3H)-quinazolinone, consistently deliver the required synthetic vectors in a series of CdII coordination polymers, allowing for reproducible supramolecular synthesis that is insensitive to the different steric and geometric demands from potentially disruptive counterions. In all nine crystallographically characterized compounds presented here, directional intermolecular N-H⋯O hydrogen bonds between ligands on adjacent complex building blocks drive the assembly and orientation of discrete building blocks into largely predictable topologies. Furthermore, whether the solids are prepared from solution or through liquid-assisted grinding, the structural o...
A Supermolecular Building Approach for the Design and Construction of Metal-Organic Frameworks
ChemInform, 2014
In this review, we describe two recently implemented conceptual approaches facilitating the design and deliberate construction of metal-organic frameworks (MOFs), namely supermolecular building block (SBB) and supermolecular building layer (SBL) approaches. Our main objective is to offer an appropriate means to assist/aid chemists and material designers alike to rationally construct desired functional MOF materials, made-to-order MOFs. We introduce the concept of net-coded building units (net-cBUs), where precise embedded geometrical information codes uniquely and matchlessly a selected net, as a compelling route for the rational design of MOFs. This concept is based on employing pre-selected 0-periodic metalorganic polyhedra or 2-periodic metal-organic layers, SBBs or SBLs respectively, as a pathway to access the requisite net-cBUs. In this review, inspired by our success with the original rht-MOF, we extrapolated our strategy to other known MOFs via their deconstruction into more elaborate building units (namely polyhedra or layers) to (i) elucidate the unique relationship between edge-transitive polyhedra or layers and minimal edge-transitive 3-periodic nets, and (ii) illustrate the potential of the SBB and SBL approaches as a rational pathway for the design and construction of 3-periodic MOFs. Using this design strategy, we have also identified several new hypothetical MOFs which are synthetically targetable.
Supramolecular Reinforcement of a Large Pore 2D Covalent Organic Framework
2021
Two dimensional covalent organic frameworks (2D-COFs) are a class of crystalline porous organic polymers that consist of covalently linked, two dimensional sheets that can stack together through non-covalent interactions. Here we report the synthesis of a novel COF, called PyCOFamide, which has an experimentally observed pore size that is greater than 6 nm in diameter. This is among the largest pore size reported to date for a 2D-COF. PyCOFamide exhibits permanent porosity and high crystallinity as evidenced by the nitrogen adsorption, powder X-ray diffraction, and high-resolution transmission electron microscopy. We show that the pore size of PyCOFamide is large enough to accommodate fluorescent proteins such as Superfolder green fluorescent protein and mNeonGreen. This work demonstrates the utility of non-covalent structural reinforcement in 2D-COFs to produce larger, persistent pore sizes than previously possible.