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Understanding Gas Storage in Cuboctahedral Porous Coordination Cages

Published

Author(s)

Gregory R. Lorzing, Eric J. Gosselin, Benjamin A Trump, Arthur H. P. York, Arni Sturluson, Casey A. Rowland, Glenn P. A. Yap, Craig Brown, Cory M. Simon, Eric D. Bloch

Abstract

Porous molecular solids are promising molecular solids are promising materials for gas storage applications. However, given the relative dearth of studies concerning these materials in this regard, additional adsorption and structural studies are vital for further understanding their properties and developing design parameters for materials optimization. Here we examine a series of isostructural cuboctahedral, paddlewheel-based coordination cages, M24(Ut^Bu-bdc)24 (M = Cr, Mo, Ru; tBu-bdc2- = 5-tert-butylisophthalic acid), for high-pressure methane storage. As the decrease in crystallinity upon activation of these porous molecular materials precludes the use of diffraction studies, we turn to a related class of pillared coordination cage-based metal-organic frameworks, M24(Me-bdc)24(dabco)6 (M= Fe, Co; Me-bdc2- = 5-methylisophthalic acid; dabco = 1,4-diazabicyclo[2.2.2.]octane) for neutron diffraction studies. The five porous materials display BET surface areas from 1,060 - 1,938 m2/g and total methane uptake capacitiesof up to a 167 cm3/cm3. Both the porous cages and cage-based frameworks display methane adsorption enthalpies of -15 to -22 kJ/mol. Neutron diffraction studies indicate that the triangular windows of the cage are optimal methane adsorption sites with CD4-arene interactions between 3.7 and 4.1 {angstrom}. At both low and high loadings three additional methane adsorption sites are apparent. These results show that M6d24^L24 cages are competent gas storage materials and further adsorption sites may be optimized by judicious ligand functionalization.
Citation
Journal of the American Chemical Society
Volume
141
Issue
30

Keywords

metal organic frameworks, gas adsorption
Created July 4, 2019, Updated October 11, 2019