Molecular tectonics of metal-organic frameworks (MOFs): a rational design strategy for unusual mixed-connected network topologies

To systematically explore the higher-dimensional network structures with mixed connectivity, a series of two-dimensional (2D) and three-dimensional (3D) metal-organic frameworks (MOFs) with unusual (3,6)-connected net topologies are presented. These crystalline materials include [{[Mn(btza)2(H2O)2].2 H2O}n] (1), [{[Zn(btza)2(H2O)2].2 H2O}n] (2), [{[Cu(btza)2].H2O}n] (3), and [{[Cd(btza)2].3 H2O}n] (4), which have been successfully assembled through a predesigned three-connected organic component bis(1,2,4-triazol-1-yl)acetate (btza) with a variety of octahedral metal cores based on the modular synthetic methodology. The topological paradigms shown in this work cover the 2D CdCl2, 3D (4(2).6)2(4(4).6(2).8(7).10(2)), and pyrite (pyr) types. That is, when properly treated with the familiar first-row divalent metal ions, btza may perfectly furnish the coordination spheres for effective connectivity to result in diverse (3,6)-connected nets. Beyond this, a detailed analysis of network topology for all known 3D (3,6)-connected frameworks in both inorganic and inorganic-organic hybrid materials is described. Specific network connectivity of these MOFs indicates that the metal centers represent the most significant and alterable factor in structural assembly, although they show reliable and similar geometries. In this context, the combination of the distinct d10 AgI ion with btza in different solvents affords two isomorphous MOFs [{[Ag(btza)].glycol}n] (5) and [{[Ag(btza)]CH3OH}n] (6) with a binodal 4-connected 3D SrAl2 (sra) topology. The network structures of MOFs 1-3 and 5 turn out to be more complicated and interesting if one considers the hydrogen bonding between the host coordination frameworks and the intercalated solvent molecules. Furthermore, the role of the included solvents in the generation and stabilization of MOFs 1-6 is also investigated.     

Control of porosity geometry in amino acid derived nanoporous materials

Substitution of the pillaring ligand in the homochiral open-framework [Ni(2)(L-asp)(2)(bipy)] by extended bipy-type ligands leads to a family of layer-structured, homochiral metal-organic frameworks. The 1D channel topology can be modified by the nature of the organic linker, with shape, cross-section and the chemical functionality tuneable. In addition, the volume of these channels can be increased by up to 36 % compared to the parent [Ni(2)(L-asp)(2)(bipy)]. The linker 1,4-dipyridylbenzene (3rbp) gives access to a new layered homochiral framework [Ni(2)(L-asp)(2)(3rbp)] with channels of a different shape. In specific cases, non-porous analogues with the linker also present as a guest can be activated to give porous materials after sublimation. Their CO(2) uptake shows an increase of up to 30 % with respect to the parent [Ni(2)(L-asp)(2)(bipy)] framework.     

Combination of MOFs and zeolites for mixed-matrix membranes

Mixed-matrix membranes (MMMs) were prepared by combinations of two different kinds of porous fillers [metal-organic frameworks (MOFs) HKUST-1 and ZIF-8, and zeolite silicalite-1] and polysulfone. In the search for filler synergy, the MMMs were applied to the separation of CO(2)/N(2), CO(2)/CH(4), O(2)/N(2), and H(2)/CH(4) mixtures and we found important selectivity improvements with the HKUST-1-silicalite-1 system (CO(2)/CH(4) and CO(2)/N(2) separation factors of 22.4 and 38.0 with CO(2) permeabilities of 8.9 and 8.4 Barrer, respectively).     

Rational design of zinc-organic coordination polymers directed by N-donor co-ligands

A family of Zn^II‐based metal–organic coordination polymers (MOCPs) [Zn(L)(imid)₂] ( 1 ), [Zn(L)(2,2′‐bpy)] ( 2 ), [Zn₂(L)₂(Py)₃] ( 3 ), [Zn(L)(DPP)]?DMF ( 4 ), [Zn(L)(DPEA)] ( 5 ), [Zn₂(L)₂(4,4′‐bpy)] ( 6 ), [Zn(L)(3,4′‐DPEE)]?DMF ( 7 ), and [Zn₃(L)₃(3,4′‐DPEE)₂]?DMF ( 8 ) (L=dithieno[3,2‐b:2′,3′‐e]benzene‐2,6‐dicarboxylic acid, imid=imidazole, bpy=bipyridine, Py=pyridine, DPP=1,3‐di(pyridin‐4‐yl)propane, DPEA=1,2‐di(pyridin‐4‐yl)ethane, and DPEE=(E)‐3,4′‐(ethene‐1,2‐diyl)dipyridine) have been rationally designed and generated in the solvothermal reaction systems of the new conjugated thiophene derivative L, Zn(ClO₄)₂?6 H₂O, and seven different aromatic N‐donor co‐ligands separately. These N‐donor compounds were carefully selected and employed in the crystal preparation of the eight MOCPs as structure‐directing co‐ligands owing to their structural specialties and habitual coordination fashions. Among these MOCPs, compounds 1 – 3 are 1D polymers with different chain structures. Compounds 4 , 7 , and 8 are 2D structures, in which 4 has two sets of twofold interpenetrating layers, whereas 7 and 8 are both built from three independent sheets. Compounds 5 and 6 are 3D frameworks, in which 5 exhibits a fivefold interpenetrating diamondoid network, whereas 6 shows a typical twofold interpenetrating pillared layer structure with nanoscale channels. The photoluminescent properties of these MOCPs, including excitation, emission, and radiactive lifetime, have also been investigated to help us tentatively understand their structure–property relationships.     

The route to a feasible hydrogen-storage material: MOFs versus ammonia borane

The replacement of fossil fuels is one of the greatest challenges that chemistry and material sciences will have to face in the near future. While hydrogen seems to be the most likely candidate for this, a material able to store the hydrogen itself is sorely needed. Intense research in the past decade has narrowed down the field of possible concepts to two materials: ammonia borane with chemically bound hydrogen atoms and metal-organic frameworks with physisorbed hydrogen molecules. Herein we want to give an overview of the strengths and weaknesses of each concept, discuss the challenges that need to be overcome, and try to compare the future capabilities of these two materials.     

Microporous metal-organic framework constructed from heptanuclear zinc carboxylate secondary building units

A novel, three-dimensional, noninterpenetrating microporous metal-organic framework (MOF), [Zn7O2(pda)5(H2O)2]5 DMF4 EtOH 6 H2O (1) (H2PDA=p-phenylenediacrylic acid, DMF=N,N-dimethylformamide, EtOH=ethanol), was synthesized by constructing heptanuclear zinc carboxylate secondary building units (SBUs) and by using rigid and linear aromatic carboxylate ligands, PDA. The X-ray crystallographic data reveals that the seven zinc centers of 1 are held together with ten carboxylate groups of the PDA ligands and four water molecules to form a heptametallic SBU, Zn7O4(CO2)10, with dimensions of 9.8 x 9.8 x 13.8 A3. Furthermore, the heptametallic SBUs are interconnected by PDA acting as linkers, thereby generating an extended network with a three-dimensional, noninterpenetrating, intersecting large-channel system with spacing of about 17.3 A. As a microporous framework, polymer 1 shows adsorption behavior that is favorable towards H2O and CH3OH, and substantial H2 uptake. In terms of the heptanuclear zinc carboxylate SBUs, polymer 1 exhibits interesting photoelectronic properties, which would facilitate the exploration of new types of semiconducting materials, especially among MOFs containing multinuclear metal carboxylate SBUs.     

Synthesis of phosphinic and phosphonic analogs of aromatic amino acids

The reaction of aryl and aralkyl aldoximes with hypophosphorous acid resulted in aminophosphinic acids, which were oxidized into the corresponding aminophosphonic acids. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 137–140, January, 1997.     

Three New MOFs Induced by Organic Linker Coordination Modes: Gas Sorption,Luminescence, and Magnetic Properties

By using a new 4,6‐bis(imidazol‐1‐yl) isophthalic acid ligand (H₂bimip) with imidazolyl and carboxyl bifunctional groups, three new MOFs, [Co(bimip)(H₂O)_0.5] ? 0.5 H₂O ( 1 ), [Zn(bimip)] ( 2 ), and [Mn(bimip)(H₂O)₂] ? H₂O ( 3 ), have been solvothermally synthesized in different solvent systems. H₂bimip displays three different coordinated modes through the imidazolyl and carboxyl groups, and different cis–cis and trans–cis configurations, which result in distinct 3D topological frameworks: a (4,8)‐connected scu net for 1 ; a twofold interpenetrated (4,4)‐connected pts net for 2 ; and a four‐connected sra net for 3 . Compounds 1 and 3 show antiferromagnetic properties, and 2 emits strong solid‐state blue luminescence. Compound 1 shows good chemical stability in acidic and basic environments and in boiling water. Additionally, the polar channels in 1 , which are decorated by uncoordinated carboxylate O atoms and imidazolyl fragments, allow it to adsorb CO₂ molecules selectively over CH₄, and the CO₂ binding sites in the framework were distinguished by molecular simulations.