There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Metal–Organic Frameworks for Separations

Luminescent Functional Metal–Organic Frameworks

New materials capable of storing hydrogen at high gravimetric and volumetric densities are required if hydrogen is to be widely employed as a clean alternative to hydrocarbon fuels in cars and other mobile applications. With exceptionally high surface areas and chemically-tunable structures, microporous metal–organic frameworks have recently emerged as some of the most promising candidate materials. In this critical review we provide an overview of the current status of hydrogen storage within such compounds. Particular emphasis is given to the relationships between structural features and the enthalpy of hydrogen adsorption, spectroscopic methods for probing framework–H2 interactions, and strategies for improving storage capacity (188 references).

/pdf/hydrogen-storage-in-metal-organic-frameworks-9ols7xj8jh.pdf

Hydrogen storage in metal–organic frameworks

Metal–organic frameworks (MOFs) display a wide range of luminescent behaviors resulting from the multifaceted nature of their structure. In this critical review we discuss the origins of MOF luminosity, which include the linker, the coordinated metal ions, antenna effects, excimer and exciplex formation, and guest molecules. The literature describing these effects is comprehensively surveyed, including a categorization of each report according to the type of luminescence observed. Finally, we discuss potential applications of luminescent MOFs. This review will be of interest to researchers and synthetic chemists attempting to design luminescent MOFs, and those engaged in the extension of MOFs to applications such as chemical, biological, and radiation detection, medical imaging, and electro-optical devices (141 references).

Luminescent Metal–Organic Frameworks

Metal-organic framework (MOF) materials, which are constructed from metal ions or metal ion clusters and bridging organic linkers, exhibit regular crystalline lattices with relatively well-defined pore structures and interesting properties. As a new class of porous solid materials, MOFs are attractive for a variety of industrial applications including separation membranes - a rapidly developing research area. Many reports have discussed the synthesis and applications of MOFs and MOF thin films, but relatively few have addressed MOF membranes. This critical review provides an overview of the diverse MOF membranes that have been prepared, beginning with a brief introduction to the current techniques for the fabrication of MOF membranes. Gas and liquid separation applications with different MOF membranes are also included (175 references).

Metal–organic framework membranes: from synthesis to separation application

Chemical functionalization of covalent organic frameworks (COFs) is critical for tuning their properties and broadening their potential applications. However, the introduction of functional groups, especially to three-dimensional (3D) COFs, still remains largely unexplored. Reported here is a general strategy for generating a 3D carboxy-functionalized COF through postsynthetic modification of a hydroxy-functionalized COF, and for the first time exploration of the 3D carboxy-functionalized COF in the selective extraction of lanthanide ions. The obtained COF shows high crystallinity, good chemical stability, and large specific surface area. Furthermore, the carboxy-functionalized COF displays high metal loading capacities together with excellent adsorption selectivity for Nd3+ over Sr2+ and Fe3+ as confirmed by the Langmuir adsorption isotherms and ideal adsorbed solution theory (IAST) calculations. This study not only provides a strategy for versatile functionalization of 3D COFs, but also opens a way to their use in environmentally related applications.

Postsynthetic Functionalization of Three-Dimensional Covalent Organic Frameworks for Selective Extraction of Lanthanide Ions.

A series of three-dimensional (3D) novel coordination polymers M(bpdc)1.5(H2O) x 0.5DMF (M = Tb (1), Ho (2), Er (3), or Y (4)) have been synthesized by reaction of the rare earth ions (M3+) with 4,4'-biphenyldicarboxylic acid (H2bpdc) in a mixed solution of DMF and C2H5OH. They possess the same 3D architectures and crystallize in monoclinic space group C2/c. Two seven-coordinated metal centers and four dimonodentate bpdc groups construct a paddle-wheel building block. These building blocks connect with two carboxyl groups to lead to a one-dimensional inorganic chain, ---M-O-C-O-M---, along the [001] direction. The inorganic chains are linked with two biphenyl groups to form 25.15 A x 17.09 A rhombic channels along the c axis without interpenetration. These complexes exhibit strong fluorescence in the visible region, and complex 3 shows Er3+ characteristic emission in the range of 1450-1650 nm at room temperature. These complexes could be anticipated as potential fluorescent probes and an IR-emitter, respectively.

Synthesis, structure and luminescent properties of rare earth coordination polymers constructed from paddle-wheel building blocks.

Two 3D chiral multifunctional microporous MOFs, Zn3(BTC)2(DMF)3(H2O).(DMF)(H2O) (1) and Cd(4)(BTC)3(DMF)2(H2O)2.6(H2O) (2) (H(3)BTC = 1,3,5-benzenetricarboxylic acid and DMF = N,N'-dimethylformamide), have been synthesized in the presence of organic bases tributylamine (TBA) and triethylamine (TEA), respectively. 1 (C(30)H(38)N(4)O(18)Zn(3)) crystallizes in the tetragonal P4(1)2(1)2 space group (a = 13.6929(19) A, c = 50.664(10) A, V = 9499(3) A(3), and Z = 8). 2 (C33H39N2O28Cd4) crystallizes in the tetragonal P4(3)22 space group (a = 10.3503(4) A, c = 52.557(3) A, V = 5630.4(4) A(3), and Z = 4). X-ray crystallography reveals that 1 consists of a 3D open framework with the (6(3))(4)(6(2).8(2).10(2))(6.(4)8(2))(2) topology, but 2 exhibits a 3D open network with the (4(2).5)(2)(4.(4)5.(10)6.(8)7.(4)8(2)) topology. The solid-state excitation-emission spectra show that the strongest excitation peaks for 1 and 2 are at 341 and 319 nm, and their emission spectra mainly show strong peaks at 410 and 405 nm, respectively. The amounts adsorbed of 1 (2) are 169 mg/g (126 mg/g) for H2O, 137 mg/g (102 mg/g) for C2H5OH, and 133 mg/g (99 mg/g) for CH3OH, which are equivalent to the adsorption of about 62 (34) H2O, 20 (11) C2H5OH, and 28 (16) CH3OH per unit cell, respectively.

Structure, luminescence, and adsorption properties of two chiral microporous metal-organic frameworks.

Covalent organic frameworks (COFs) are an emerging class of porous crystalline polymers with broad potential applications. So far, the availability of three-dimensional (3D) COFs is limited and more importantly only one type of covalent bond has been successful used for 3D COF materials. Here, we report a new synthetic strategy based on dual linkages that leads to 3D COFs. The obtained 3D COFs show high specific surface areas and large gas uptake capacities, which makes them the top COF material for gas uptake. Furthermore, we demonstrate that the new 3D COFs comprise both acidic and basic sites, and act as excellent bifunctional catalysts for one-pot cascade reactions. The new synthetic strategy provides not only a general and versatile approach to synthesize 3D COFs with sophisticated structures but also expands the potential applications of this promising class of porous materials.

Ming Xue

Papers

Metal–organic framework membranes: from synthesis to separation application

Postsynthetic Functionalization of Three-Dimensional Covalent Organic Frameworks for Selective Extraction of Lanthanide Ions.

Synthesis, structure and luminescent properties of rare earth coordination polymers constructed from paddle-wheel building blocks.

Structure, luminescence, and adsorption properties of two chiral microporous metal-organic frameworks.

Three-Dimensional Covalent Organic Frameworks with Dual Linkages for Bifunctional Cascade Catalysis