Showing papers by "Mohamed Eddaoudi published in 2011"

The next chapter in MOF pillaring strategies: trigonal heterofunctional ligands to access targeted high-connected three dimensional nets, isoreticular platforms.

Abstract: A new pillaring strategy, based on a ligand-to-axial approach that combines the two previous common techniques, axial-to-axial and ligand-to-ligand, and permits design, access, and construction of higher dimensional MOFs, is introduced and validated. Trigonal heterofunctional ligands, in this case isophthalic acid cores functionalized at the 5-position with N-donor (e.g., pyridyl- or triazolyl-type) moieties, are designed and utilized to pillar pretargeted two-dimensional layers (supermolecular building layers, SBLs). These SBLs, based on edge transitive Kagome and square lattices, are cross-linked into predicted three-dimensional MOFs with tunable large cavities, resulting in isoreticular platforms.

Network Diversity through Decoration of Trigonal-Prismatic Nodes: Two-Step Crystal Engineering of Cationic Metal-Organic Materials**

Abstract: During the past decade porous metal–organic material (MOM) networks constructed from metal-based nodes (metal ions or metal clusters) and bridging organic ligand (linkers) have attracted ever increasing scientific interest. Their modular nature imparts structural and compositional diversity, tunable functionality, and multiple properties within a single material. In particular, that MOMs can exhibit extralarge surface area means that they represent a uniquely promising class of materials to solve technological challenges related to gas storage and separation, environmental remediation, catalysis, sensing, and drug delivery. Crystal engineering played a major role in the early development of MOMs as exemplified by the high symmetry nets that can be generated by linking polygonal or polyhedral nodes such as tetrahedra (dia), octahedra (pcu), squares (nbo), and trigonal prisms (acs). The aforementioned nets might be described as platforms because they are fine-tunable in terms of both scale and properties as there are many nodes and linkers that can sustain these structures. Pyridyl linkers such as 4,4’-bipyridine were initially exploited in such a capacity but the majority of extra-large surface area MOMs are based upon carboxylate linkers such as benzene-1,3-dicarboxylic acid (1,3-BDC), benzene-1,4-dicarboxylic acid (1,4-BDC), and benzene-1,3,5-tricarboxylic acid (BTC). Such linkers complement synthetically accessible and highly symmetrical metal carboxylate nodes such as [Cu2(CO2)4], [Zn4(m4-O)(CO2)6] and [{M3(m3-O)(CO2)}6] (M=Cr, Fe). The exploitation of [Cu2(CO2)4], the “square paddlewheel”, has proven to be particularly fruitful since ligand design or the use of mixed ligands facilitates a plethora of highly porous polyhedral nets. [{M3(m3-O)(CO2)}6] , the “trigonal prism”, has also afforded highly porous materials, as exemplified by MIL-100 and MIL-101. However, even though this node is remarkably robust, its structures tend to form only microcrystalline materials and require harsh synthetic conditions. We describe herein a crystal engineering strategy that exploits preformed molecular building blocks (MBBs) based upon water-stable trigonal prisms that are decorated with pyridyl moieties. A two-step modular approach that opens up a broad new class of bimetallic MOMs is thereby facilitated. Two-step processes to form heterobimetallic frameworks are known and are based on the synthesis of a metal complex that is subsequently connected to a different metal ion. To the best of our knowledge, high-connectivity metal complexes that afford high symmetry nets with extra-large channels have not yet been studied in this context. Our twostep process involves isolation of a trigonal prism decorated by pyridyl moieties and then coordinating this highly soluble trigonal-prismatic Primary Molecular Building Block (tpPMBB-1) to different metals through its six exodentate pyridyl moieties (Scheme 1). We coin the term PMMB to draw analogies to the primary building unit (PBU) in zeolite chemistry. In this context the different connections of PMBBs to various Secondary Molecular Building Blocks (SMBBs) lead to the structural diversity. This approach enables us to exploit both metal–carboxylate and metal–pyridyl bonds and ensures that the nets thereby generated will be positively charged. The first three examples of such nets, tp-PMBB-1snx-1, -snw-1, and -stp-1 (nomenclature describes both the primary building block and the topology of the resulting net) are described herein. The building block tp-PMBB-1 [Cr3(m3-O)(isonic)6] + (isonic= pyridine-4-carboxylate) represents a discrete and robust “hexapyridyl” 6-connected node that is well-suited for the subsequent synthesis of a plethora of networks with nanoscale features. Its coordination chemistry with two metals is detailed herein: a linear but bendable linker (Ag) and a rigid square-planar metal node (Cd). Our results demonstrate the ability of Ag to exist in nonlinear geometry and facilitate two new network topologies for trigonalprismatic nodes, snx (six-connected net type x) (6,6) and snw (six-connected net type w) (6,6), rather than the default acs net. A cationic net with acs topology formed by another tp-PMBB can also be formed and will be reported elsewhere. For the rigid CdN4 node we anticipated stp (square trigonal prism) (6,4) topology consisting of a trigonal-prismatic and a rectangular-vertex figure, and the first nanoporous variant of this net was indeed isolated. [*] A. Schoedel, Dr. L. Wojtas, Prof. Dr. M. J. Zaworotko Department of Chemistry, University of South Florida 4202 East Fowler Ave., SCA400, Tampa, FL 33620 (USA) E-mail: xtal@usf.edu Homepage: http://chemistry.usf.edu/faculty/zaworotko/

The Quest for Modular Nanocages: tbo-MOF as an Archetype for Mutual Substitution, Functionalization, and Expansion of Quadrangular Pillar Building Blocks

Abstract: A new blueprint network for the design and synthesis of porous, functional 3D metal-organic frameworks (MOFs) has been identified, namely, the tbo net. Accordingly, tbo-MOFs based on this unique (3,4)-connected net can be exclusively constructed utilizing a combination of well-known and readily targeted [M(R-BDC)](n) MOF layers [i.e., supermolecular building layers (SBLs)] based on the edge-transitive 4,4 square lattice (sql) (i.e., 2D four-building units) and a novel pillaring strategy based on four proximal isophthalate ligands from neighboring SBL membered rings (i.e., two pairs from each layer) covalently cross-linked through an organic quadrangular core (e.g., tetrasubstituted benzene). Our strategy permits the rational design and synthesis of isoreticular structures, functionalized and/or expanded, that possess extra-large nanocapsule-like cages, high porosity, and potential for gas separation and storage, among others. Thus, tbo-MOF serves as an archetypal tunable, isoreticular MOF platform for targeting desired applications.

Symbiosis of zeolite-like metal–organic frameworks (rho-ZMOF) and hydrogels: Composites for controlled drug release

Abstract: The design and synthesis of new finely tunable porous materials has spurred interest in developing novel uses in a variety of systems. Zeolites, inorganic materials with high thermal and mechanical stability, in particular, have been widely examined for use in applications such as catalysis, ion exchange and separation. A relatively new class of inorganic–organic hybrid materials known as metal–organic frameworks (MOFs) have recently surfaced, and many have exhibited their efficiency in potential applications such as ion exchange and drug delivery. A more recent development is the design and synthesis of a subclass of MOFs based on zeolite topologies (i.e. ZMOFs), which often exhibit traits of both zeolites and MOFs. Bio-compatible hydrogels already play an important role in drug delivery systems, but are often limited by stability issues. Thus, the addition of ZMOFs to hydrogel formulations is expected to enhance the hydrogel mechanical properties, and the ZMOF–hydrogel composites should present improved, symbiotic drug storage and release for delivery applications. Herein we present the novel composites of a hydrogel with a zeolite-like metal–organic framework, rho-ZMOF, using 2-hydroxyethyl methacrylate (HEMA), 2,3-dihydroxypropyl methacrylate (DHPMA), N-vinyl-2-pyrolidinone (VP) and ethylene glycol dimethacrylate (EGDMA), and the corresponding drug release. An ultraviolet (UV) polymerization method is employed to synthesize the hydrogels, VP 0, VP 15, VP 30, VP 45 and the ZMOF-VP 30 composite, by varying the VP content (mol%). The rho-ZMOF, VP 30, and ZMOF-VP 30 composite are all tested for the controlled release of procainamide (protonated, PH), an anti-arrhythmic drug, in phosphate buffer solution (PBS) using UV spectroscopy.

Insight into the construction of metal–organic polyhedra: metal–organic cubes as a case study

Abstract: Systematic studies were conducted to gain a better understanding of the metal–organic cubes (MOCs) directed assembly and their crystallization under predetermined reaction conditions, i.e. charge and size of metal ions, solvent type, counter anions, pH, and temperature. Four novel metal–organic materials are constructed via solvothermal reactions of different metal ions and 2,2′-(1H-imidazole-4,5-diyl)di-1,4,5,6-tetrahydropyrimidine, namely [Co8(C11N6H15)12]Cl12·4H2O (1), [Ni4(C11N6H15)4](NO3)4·4DMF (2), {Cd(C11N6H15)(NO3)·DMF}n (3), and [In8(C11N6H15)12](NO3)12·4H2O (4). In addition, syntheses and crystal structures for compounds 1(a–f), constructed under deliberately modified reaction conditions of 1, are reported. In compounds 1(a–f), the CoIII-based cationic MOCs crystallize in various packing arrangements in the presence of different counter-ions. Discrete MOCs retain their structural integrity, when crystalline solid was dissolved in water, under various pH (2.03–8.07) and temperatures (298–333 K), as confirmed by solution NMR studies. The assembly of the discrete MOC, from its basic molecular building blocks under mild reaction conditions, is demonstrated and monitored through solution NMR and UV-vis studies.

Cocrystal controlled solid-state synthesis of a rigid tetracarboxylate ligand that pillars both square grid and Kagomé lattice layers

Abstract: [Cu2(carboxylate)4] paddlewheel molecular building blocks, MBBs, are capable of generating square grid or Kagome lattice supramolecular isomers when dicarboxylates such as 1,3-benzenedicarboxylate (1,3-bdc) and 1,4-benzenedicarboxylate (1,4-bdc) are exploited to link the paddlewheel MBBs. In this contribution we demonstrate that it is possible to use a solvent-free reaction (cocrystal controlled solid-state synthesis) to prepare a tetracarboxylic acid, H44BIPA-TC, formed by rigidly linking two 1,3-bdc moieties at the 5-position. BIPA-TC can pillar both square grid and Kagome lattice supramolecular isomers, thereby generating nets that exhibit lvt or nbo topologies, respectively.

Crystal Engineering Using a “Turtlebug” Algorithm: A de Novo Approach to the Design of Binodal Metal–Organic Frameworks

Abstract: A new series of computer programs that enumerate three-dimensional periodic embedded nets (i.e., representing crystals) is based on an algorithm that can theoretically enumerate all possible struct...