Zeolitic Boron Imidazolate Frameworks

Dual-Step Redox Engineering of 2D CoNi-Alloy Embedded B, N-Doped Carbon Layers Toward Tunable Electromagnetic Wave Absorption and Light-Weight Infrared Stealth Heat Insulation Devices

2D layered metallic graphite composites are promising electromagnetic wave absorption materials (EWAMs) for their combined properties of abundant interlayer free spaces, rich metallic polarized sites, and high conductivity, but the controllable synthesis remains rather challenging. Herein, a dual-step redox engineering strategy is developed by employing cobalt boron imidazolate framework (Co-BIF) to construct 2D CoNi-alloy embedded B, N-doped carbon layers (2D-CNC) as a promising EWAM. In the first step, a chemical etching oxidation process on Co-BIF is used to obtain an optimized 2D-CoNi-layered double hydroxide (2D-CoNi-LDH) intermediate and in the second, high-temperature calcination reduction is implemented to modify graphitization of the degree of the 2D-CNC. The obtained sample delivers superior reflection loss (RLmin) of -60.1 dB and wide effective absorption bandwidth (EAB) of 6.24 GHz. The synergy mechanisms of interfacial/dipole polarization and magnetic coupling are in-depth evidenced by the hologram and Lorentz electron microscopy, revealing its significant contribution on multireflection and impedance matching. Further theoretical evaluation by COMSOL simulation in different fields based on the dynamic loss process toward the test ring reveals the in situ EW attenuation process. This work presents a strategy to develop multifunctional light-weight infrared stealthy aerogel with superior pressure-resistant, anti-corrosion, and heat-insulating properties for future applications.

BN-Doped Metal-Organic Frameworks: Tailoring 2D and 3D Porous Architectures through Molecular Editing of Borazines

Building on the MOF approach to prepare porous materials, herein we report the engineering of porous BN-doped materials using tricarboxylic hexaarylborazine ligands, which are laterally decorated with functional groups at the full-carbon 'inner shell'. Whilst an open porous 3D entangled structure could be obtained from the double interpenetration of two identical metal frameworks derived from the methyl substituted borazine, the chlorine-functionalised linker undergoes formation of a porous layered 2D honeycomb structure, as shown by single-crystal X-ray diffraction analysis. In this architecture, the borazine cores are rotated by 60° in alternating layers, thus generating large rhombohedral channels running perpendicular to the planes of the networks. An analogous unsubstituted full-carbon metal framework was synthesised for comparison. The resulting MOF revealed a crystalline 3D entangled porous structure, composed by three mutually interpenetrating networks, hence denser than those obtained from the borazine linkers. Their microporosity and CO2 uptake were investigated, with the porous 3D BN-MOF entangled structure exhibiting a large apparent BET specific surface area (1091 m2  g-1 ) and significant CO2 reversible adsorption (3.31 mmol g-1 ) at 1 bar and 273 K.

Disappearing Polymorphs in Metal-Organic Framework Chemistry: Unexpected Stabilization of a Layered Polymorph over an Interpenetrated Three-Dimensional Structure in Mercury Imidazolate

The "disappearing polymorph" phenomenon is well established in organic solids, and has had a profound effect in pharmaceutical materials science. The first example of this effect in metal-containing systems in general, and in coordination-network solids in particular, is here reported. Specifically, attempts to mechanochemically synthesize a known interpenetrated diamondoid (dia) mercury(II) imidazolate metal-organic framework (MOF) yielded a novel, more stable polymorph based on square-grid (sql) layers. Simultaneously, the dia-form was found to be highly elusive, observed only as a short-lived intermediate in monitoring solvent-free synthesis and not at all from solution. The destabilization of a dense dia-framework relative to a lower dimensionality one is in contrast to the behavior of other imidazolate MOFs, with periodic density functional theory (DFT) calculations showing that it arises from weak interactions, including structure-stabilizing agostic C-H⋅⋅⋅Hg contacts. While providing a new link between MOFs and crystal engineering of organic solids, these findings highlight a possible role for agostic interactions in directing topology and stability of MOF polymorphs.

Construction of Zeolite-Like Cluster Organic Frameworks from 3 d-4 d/3 d-3 d Heterometallic Supertetrahedral Secondary Building Units: Syntheses, Structures, and Properties

Two zeolite-like cluster organic frameworks based on Cd-Cu/Mn-Cu heterometallic supertetrahedral secondary building units have been successfully constructed under solvothermal conditions, namely, Cu[Cd₄ Cu₆ (L)₄ (H₂ O)₁₈ ](Ac)₉ ⋅DMA⋅3 H₂ O (1), and Cu[Mn₄ Cu₆ (L)₄ (Ac)₃ (H₂ O)₁₂ ](Ac)₆ ⋅CH₃ CN⋅13 H₂ O (2), where H₃ L=2-(hydroxymethyl)-2-(pyridin-4-yl)-1,3-propanediol, Ac=CH₃ COO^- , DMA=N,N'-dimethylacetamide. Single-crystal X-ray structural analysis reveals that both 1 and 2 exhibit 3-dimensional zeolite-like architectures with similar 4-connected components, but possess definitely different topologies of diamondoid (dia) and uncommon lonsdaleite (lon), respectively. 1 and 2 represent the first cases of zeolite-like cluster organic frameworks containing Cd-Cu/Mn-Cu heterometallic supertetrahedral secondary building units. Furthermore, the magnetic properties and porous nature of 1 and 2 were also studied.

Multiple-Site SO2 -Capture Ionic Liquids with Nearly Uniform Site Performance

We propose a series of azolium poly(azolyl)borate ionic liquids (ILs) for reversible SO₂ capture. Density functional calculations demonstrate that the designed borate anions can strongly bond to SO₂ at multiple sites with nearly uniform binding energies. Thus, as well as high overall uptakes, the ILs can achieve much higher effective uptakes (the uptake difference between absorption and desorption conditions) than existing SO₂ -capture reagents. The larger size of the borate anions, the evenly distributed negative charge among the azolyl rings, and the blocking of the conjugation by the tetrahedral boron concertedly reduce absorbate-absorbate repulsion, which leads to a large disparity among binding sites in other multiple-site SO₂ sorbents.

Zeolitic imidazolate frameworks: next-generation materials for energy-efficient gas separations

Industrial separation processes comprise approximately 10% of the global energy demand, driven largely by the utilization of thermal separation methods (e.g., distillation). Significant energy and cost savings can be realized using advanced separation techniques such as membranes and sorbents. One of the major barriers to acceptance of these techniques remains creating materials that are efficient and productive in the presence of aggressive industrial feeds. One promising class of emerging materials is zeolitic imidazolate frameworks (ZIFs), an important thermally and chemically stable subclass of metal organic frameworks (MOFs). The objectives of this paper are (i) to provide a current understanding of the synthetic methods that enable the immense tunability of ZIFs, (ii) to identify areas of success and areas for improvement when ZIFs are used as adsorbents, (iii) to identify areas of success and areas for improvement in ZIF membranes. A review is given of the state-of-the-art in ZIF synthesis procedures and novel ZIF formation pathways as well as their application in energy efficient separations.

Zeolitic boron imidazolate frameworks with 4-connected octahedral metal centers

Solvent selection! The organically templated co-assembly between tetrahedral [B(imidazolate)(4)](-) and [Co(ac)](+) units leads to two previously unknown zeolitic boron imidazolate frameworks with ACO and ABW topologies (denoted BIF-22 and BIF-23; e-urea = ethyleneurea), respectively. BIF-22 is chiral and shows interesting CO(2) selectivity over N(2) and CH(4).

Temperature-/pressure-dependent selective separation of CO(2) or benzene in a chiral metal-organic framework material

Presented here is a chiral microporous metal-organic framework material with a three-fold interpenetrating diamond-type structural topology and interesting properties for selective separation. The material has a high storage capacity for CO(2) gas (4.23 mmol g(-1) at 273 K and 1 bar) and shows fantastic temperature-dependent selectivity for CO(2) over N(2). Moreover, this multifunctional material, which has a rich π system, can selectively adsorb benzene over cyclohexane at low pressure (0.05 bar) at 298 K.

2:1 cocrystals of homochiral and achiral amino acid zwitterions with Li+ salts: water-stable zeolitic and diamondoid metal-organic materials

Eight 2:1 cocrystals of amino acid zwitterions and Li(+) salts were crystallized from hot water to afford cationic networks based on tetrahedral lithium cations: square grids, an ABW topology net, and diamondoid nets.

Porous metal carboxylate boron imidazolate frameworks

Integrated Material for Efficient CO2 Storage A new family of porous materials with tunable gas sorption properties have been made by integrating metal carboxylates and boron imidazolates under hydro- or solvothermal conditions. One hydrothermally synthesized phase exhibits a very high volumetric CO2 storage capacity at 81 L/L (273K, 1atm).