Open Metal Sites within Isostructural Metal–Organic Frameworks for Differential Recognition of Acetylene and Extraordinarily High Acetylene Storage Capacity at Room Temperature

Abstract

Open metal sites have played very important roles in synthetic assemblies and biological systems because of their specific recognition of small molecules and thus for their highly selective molecular transformations, transport, and storage. [1][2][3][4] Understanding the molecular recognition between the open metal sites and the substrate molecules at the molecular level will not only facilitate the discoveries of new catalysts, sensing, and storage materials, but will also provide a deep insight in the functions of the open metal sites in the biological systems and thus stimulate studies of modeling compounds to mimic biological functions. However, the highly reactive nature of such open metal sites has mainly limited our capacities to elucidate the metal-substrate recognition processes fundamentally and systematically within molecular assemblies. This situation changed recently with the emergence of porous metal-organic frameworks (MOFs) with sustained open metal sites, which provided the promise of elucidating the bonding nature of the open metal sites with small gas molecules at the molecular level. [5][6][7] We realized that open Cu 2+ sites within a porous HKUST-1 material have strong interactions with acetylene molecules (the adsorption enthalpy is 30.4 kJ mol À1 at a coverage of 1 mmol g À1 ) and thus contribute significantly to the high acetylene storage with a volumetric storage capacity of 177 cm 3 cm À3 at 295 K and 1 atm. [8] Because acetylene is a very important raw material for various industrial chemicals, fundamental studies on the metal site-acetylene interactions and their bonding nature will promote the discovery of new chemical transformations for the efficient usage of acetylene and new porous materials for high acetylene storage capacity.[9] The highly explosive nature of acetylene has limited the possible storage materials to fulfill high acetylene storage capacities at room temperature and at pressures of under 0.2 MPa (the compression limit for the safe storage of acetylene). It is thus particularly important to target systems having very strong interactions with acetylene to secure high acetylene storage capacities.[ The temperature-dependent acetylene adsorption isotherms of these isostructural MOFs were examined to evaluate their adsorption enthalpies and thus their different interactions with acetylene molecules. The examined MOFs show repeatable adsorption isotherms.[22] The coverage-dependent adsorption enthalpies of the MOFs to acetylene were calculated based on a virial method, a well established and reliable methodology from fits of their adsorption isotherms at 273 and 295 K.[23] As shown in Figure 1

Materials genomics‐guided ab initio screening of MOFs with open copper sites for acetylene storage

“…As then, design and synthesis of high‐performance MOFs has become an increasingly hot research topic in the field of C 2 H 2 storage. Considering the compression limit of C 2 H 2 , one strategy commonly adopted to enhance guest‐host interactions is introducing open metal sites (OMS) into MOFs . Among such subset of MOFs, immobilization of open Cu sites using the secondary building unit (SBU) of dicopper paddle‐wheel Cu 2 (COO) 4 was found to be an effective approach .…”

Analyzing the frequency shift of physiadsorbed CO2in metal organic framework materials

“…In order to design new MOFs with improved properties, it is of critical importance to understand the nature of the interaction between the absorbed molecule and the MOF host. Such understanding can either be gained through theory, using first-principles simulations, [8][9][10][11][12][13][14][15][16][17][18] or through experimental probes, such as infrared (IR) absorption and Raman scattering. [8][9][10][11]18,[20][21][22][23][24] Much progress has been made in improving the properties of MOFs.…”

“…For example, it has been shown that using unsaturated metal centers, such as MOF74 with open Mg, Mn, Zn, Ni, Cu, or HKUST-1 with Cu, results in higher absorption density for hydrogen and faster absorption at small partial CO 2 pressures, the latter of which is highly desirable for CO 2 capturing applications. [5][6][7][8][9][14][15][16][17][19][20][21][22] It has further been shown that iso-structural MOFs with different open metal centers can have very different absorption rates at low pressure. 7 In particular, the electronically similar metal centers Mg and Zn result in a much faster CO 2 uptake rate in Mg-MOF74 than in Zn-MOF74 at a pressure smaller than 0.1 atm.…”

MOFs as reactant: In situ synthesis of Li2ZnTi3O8@C–N nanocomposites as high performance anodes for lithium-ion batteries

“…Metal-organic frameworks (MOFs), assembled by inorganic vertices (metal ions or clusters) and organic linkers, have attracted extensive research interest because of their diverse structural topologies, tunable functionalities, as well as versatile applications in catalysis [40][41][42][43], biomedical imaging [44,45], gas separation and storage [46][47][48]. Moreover, inspired by their high surface areas, porosity, and abundant carboncontaining linkers, MOFs have been demonstrated as promising templates or precursors to fabricate nanostructured materials via thermolysis [49][50][51][52][53][54][55][56][57][58][59][60].…”