Kyoungmoo Koh

Screening of Metal−Organic Frameworks for Carbon Dioxide Capture from Flue Gas Using a Combined Experimental and Modeling Approach

A diverse collection of 14 metal-organic frameworks (MOFs) was screened for CO(2) capture from flue gas using a combined experimental and modeling approach. Adsorption measurements are reported for the screened MOFs at room temperature up to 1 bar. These data are used to validate a generalized strategy for molecular modeling of CO(2) and other small molecules in MOFs. MOFs possessing a high density of open metal sites are found to adsorb significant amounts of CO(2) even at low pressure. An excellent correlation is found between the heat of adsorption and the amount of CO(2) adsorbed below 1 bar. Molecular modeling can aid in selection of adsorbents for CO(2) capture from flue gas by screening a large number of MOFs.

A Porous Coordination Copolymer with over 5000 m2/g BET Surface Area

New levels of surface area are achieved in a coordination polymer (UMCM-2, University of Michigan Crystalline Material) derived from zinc-mediated coordination copolymerization of a dicarboxylic and tricarboxylic acid. In addition to a large micropore contribution to the surface area, mesopores are also present. In contrast to the recently reported coordination copolymer UMCM-1, which has a mesoporous channel, UMCM-2 is built from three types of cages. In spite of exceptional porosity, both of these coordination polymers are thermally robust. Hydrogen uptake performance of UMCM-2 approaches 7 wt% at 77 K.

MOF@MOF: microporous core–shell architectures

Mixing two different linkers with the same topology has been applied to make metal-organic frameworks (MOFs) either in one batch or sequentially to generate coordination copolymers with either a randomly mixed or a core-shell composition of linkers.

Highly Dispersed Palladium(II) in a Defective Metal–Organic Framework: Application to C–H Activation and Functionalization

High reversibility during crystallization leads to relatively defect-free crystals through repair of nonperiodic inclusions, including those derived from impurities. Microporous coordination polymers (MCPs) can achieve a high level of crystallinity through a related mechanism whereby coordination defects are repaired, leading to single crystals. In this work, we discovered and exploited the fact that this process is far from perfect for MCPs and that a minority ligand that is coordinatively identical to but distinct in shape from the majority linker can be inserted into the framework, resulting in defects. The reaction of Zn(II) with 1,4-benzenedicarboxylic acid (H(2)BDC) in the presence of small amounts of 1,3,5-tris(4-carboxyphenyl)benzene (H(3)BTB) leads to a new crystalline material, MOF-5(O(h)), that is nearly identical to MOF-5 but has an octahedral morphology and a number of defect sites that are uniquely functionalized with dangling carboxylates. The reaction with Pd(OAc)(2) impregnates the metal ions, creating a heterogeneous catalyst with ultrahigh surface area. The Pd(II)-catalyzed phenylation of naphthalene within Pd-impregnated MOF-5(O(h)) demonstrates the potential utility of an MCP framework for modulating the reactivity and selectivity of such transformations. Furthermore, this novel synthetic approach can be applied to different MCPs and will provide scaffolds functionalized with catalytically active metal species.

A framework for predicting surface areas in microporous coordination polymers.

A predictive tool termed the linker to metal cluster (LiMe) ratio is introduced as a method for understanding surface area in microporous coordination polymers (MCPs). Calibrated with geometric accessible surface area computations, the LiMe ratio uses molecular weight of building block components to indicate the maximum attainable surface area for a given linker and metal cluster combination. MOF-5 and HKUST-1 are used as prototypical structures to analyze MCPs with octahedral M(4)O(CO(2)R)(6) and paddlewheel M(2)(CO(2)R)(4) metal clusters. Insight into the effects of linker size, geometry, number of coordinating groups, and framework interpenetration is revealed through the LiMe ratio analysis of various MCPs. Experimental surface area deviation provides indication that a material may suffer from incomplete guest removal, structural collapse, or interpenetration. Because minimal data input are required, the LiMe ratio surface area analysis is suggested as a quick method for experimental verification as well as a guide for the design of new materials.

Exceptional surface area from coordination copolymers derived from two linear linkers of differing lengths

Although a multitude of microporous coordination polymers (MCPs) with ultrahigh surface area have been reported in the last decade, none of these can come close to matching the cost/performance ratio of conventional sorbents such as zeolites and carbons for most applications. There is a need to drastically reduce the cost of MCPs and this goal cannot be achieved through complex linker synthesis strategies so often used to boost MCP performance. Here two new MCPs: UMCM-8 (Zn4O(benzene-1,4-dicarboxylate)1.5(naphthalene-2,6-dicarboxylate)1.5), and UMCM-9 (Zn4O(naphthalene-2,6-dicarboxylate)1.5(biphenyl-4,4′-dicarboxylate)1.5) are described and the concept of using mixtures of readily available linear linkers that enforce different spacings between network nodes is introduced as a means to reduce interpenetration. These new MCPs demonstrate Brunauer–Emmett–Teller (BET) surface areas over 4000 m2 g−1 and high pore volumes over 1.80 cm3 g−1.

Heterogeneous Single-Molecule Diffusion in One-, Two-, and Three-Dimensional Microporous Coordination Polymers: Directional, Trapped, and Immobile Guests

The diffusion of individual Nile red molecules in three different crystalline microporous coordination polymers (MCPs) is visualized with single-molecule fluorescence microscopy. By localizing molecules with high spatial resolution, the trajectories of the diffusing dyes are reconstructed with nanometer-scale precision. A detailed analysis of these tracks reveals different dynamics and guest-host interactions in each crystal as well as distinct motion types within the same system, suggesting the presence of structural heterogeneities in local environments.

Porous Solids Arising from Synergistic and Competing Modes of Assembly: Combining Coordination Chemistry and Covalent Bond Formation†

Design and synthesis of porous solids employing both reversible coordination chemistry and reversible covalent bond formation is described. The combination of two different linkage modes in a single material presents a link between two distinct classes of porous materials as exemplified by metal-organic frameworks (MOFs) and covalent organic frameworks (COFs). This strategy, in addition to being a compelling material-discovery method, also offers a platform for developing a fundamental understanding of the factors influencing the competing modes of assembly. We also demonstrate that even temporary formation of reversible connections between components may be leveraged to make new phases thus offering design routes to polymorphic frameworks. Moreover, this approach has the striking potential of providing a rich landscape of structurally complex materials from commercially available or readily accessible feedstocks.