Computational Screening of MOFs with Open Metal Sites
Emmanuel Haldoupis1, Konstantinos D. Vogiatzis1, Laura Gagliardi1, J. Ilja Siepmann1,2
1Department of Chemistry and Chemical Theory Center, University of Minnesota, Minneapolis, Minnesota 55455, United States
2Department of Chemical Engineering and Materials Science, University of Minnesota, 421 Washington Avenue SE, Minneapolis, Minnesota 55455, USA
Metal-organic frameworks (MOFs), among other nanoporous materials, are of potential utility for many energy-relevant or technologically important processes, such as adsorption and catalysis. Specifically undercoordinated metal centers, often found in MOFs, can interact strongly and selectively with certain guest molecules. These strong interactions may involve partial bond formation leading to highly selective separations compared to MOFs with fully coordinated metal centers and allowing for catalytic activation for various reactions. Computational high-throughput screening of materials can be used to assess the performance of thousands of materials. However, correctly modeling the strong interaction of guest molecules with open metal centers requires the use of expensive quantum chemical methods and reduces the number of materials that can be examined. To mitigate this challenge we have developed a computational tool that analyzes the atomic coordinates of MOFs, identifies the presence of patterns corresponding to open metal sites with sufficient guest accessibility and, hence, reduces the number of materials that need to be examined using more expensive computational methods. Recently a database containing more than 5000 computation-ready experimental (CoRE) MOF structures with a pore limiting diameter of at least 2.4 Å was reported . After screening this database and identified all MOFs with open metal sites we concentrate on MOFs containing Mg and Fe open metal sites. We identify 51 MOFs with unsaturated Mg sites and assessed their CO2/N2 adsorption selectivites using periodic DFT calculations. In addition, 43 MOFs with coordinatively unsaturated iron centers are identified and examined by means of electronic structure theory for the stability of the highly reactive Fe(IV)-oxo intermediate.
 Y. G. Chung, J. Camp, M. Haranczyk, B. J. Sikora, W. Bury, V. Krungleviciute, T. Yildirim, O. K. Farha, D. S. Sholl and R. Q. Snurr, ``Computation-Ready, Experimental Metal-Organic Frameworks: A Tool To Enable High-Throughput Screening of Nanoporous Crystals'', Chemistry of Materials, 2014, 26, 6185-6192.
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