Comprehensive study of carbon dioxide adsorption in the metal–organic frameworks M2(dobdc) (M = Mg, Mn, Fe, Co, Ni, Cu, Zn)

Wendy L. Queen, Matthew R. Hudson, Eric D. Bloch, Jarad A. Mason, Miguel I. Gonzalez, Jason S. Lee, David Gygi, Joshua D. Howe, Kyuho Lee, Tamim A. Darwish, Michael James, Vanessa K. Peterson (+5 others)
2014 Chemical Science  
The results reveal important, molecular level detail of CO 2 binding in a prominent family of Metal-Organic Frameworks whose adsorption properties can be readily tuned with metal-substitution. This information, which is of signifi cant importance in the context of carbon capture, allows us to make a detailed comparison with DFT calculations; theoretical results show excellent agreement with experimental determination of intramolecular CO 2 angles, CO 2 binding geometries, and isosteric heats of
more » ... isosteric heats of CO 2 adsorption. Analysis of the CO 2 adsorption properties of a well-known series of metal-organic frameworks M 2 (dobdc) (dobdc 4À ¼ 2,5-dioxido-1,4-benzenedicarboxylate; M ¼ Mg, Mn, Fe, Co, Ni, Cu, and Zn) is carried out in tandem with in situ structural studies to identify the host-guest interactions that lead to significant differences in isosteric heats of CO 2 adsorption. Neutron and X-ray powder diffraction and single crystal X-ray diffraction experiments are used to unveil the site-specific binding properties of CO 2 within many of these materials while systematically varying both the amount of CO 2 and the temperature. Unlike previous studies, we show that CO 2 adsorbed at the metal cations exhibits intramolecular angles with minimal deviations from 180 , a finding that indicates a strongly electrostatic and physisorptive interaction with the framework surface and sheds more light on the ongoing discussion regarding whether CO 2 adsorbs in a linear or nonlinear geometry. This has important implications for proposals that have been made to utilize these materials for the activation and chemical conversion of CO 2 . For the weaker CO 2 adsorbents, significant elongation of the metal-O(CO 2 ) distances are observed and diffraction experiments additionally reveal that secondary CO 2 adsorption sites, while likely stabilized by the population of the primary adsorption sites, significantly contribute to adsorption behavior at ambient temperature. Density functional theory calculations including van der Waals dispersion quantitatively corroborate and rationalize observations regarding intramolecular CO 2 angles and trends in relative geometric properties and heats of adsorption in the M 2 (dobdc)-CO 2 adducts. Fig. 1 Ball and stick model of the M 2 (dobdc) structure type showing the MO 5 polyhedron and (dobdc) 4À linker. Orange, red, grey, and black spheres represent the metal, oxygen, carbon, and hydrogen, respectively. 4570 | Chem. Sci., 2014, 5, 4569-4581 This journal is
doi:10.1039/c4sc02064b fatcat:hyqc7b3zvvanxg4gwdpxm7nn7m