Hydrogen Storage and Carbon Dioxide Capture in an Iron-based Sodalite-type Metal-organic Framework (Fe-BTT) Discovered via High-throughput Methods
Using high-throughput instrumentation to screen conditions, the reaction between FeCl 2 and H 3BTT·2HCl (BTT 3- = 1,3,5-benzenetristetrazolate) in a mixture of DMF and DMSO was found to afford Fe 3[(Fe 4Cl) 3(BTT) 8] 2·22DMF·32DMSO·11H 2O. This compound adopts a porous three-dimensional framework structure consisting of square [Fe 4Cl] 7+ units linked via triangular BTT 3- bridging ligands to give an anionic 3,8-net. Mössbauer spectroscopy carried out on a DMF-solvated version of the material indicated the framework to contain high-spin Fe 2+ with a distribution of local environments and confirmed the presence of extra-framework iron cations. Upon soaking the compound in methanol and heating at 135 °C for 24 h under dynamic vacuum, most of the solvent is removed to yield Fe 3[(Fe 4Cl) 3(BTT) 8(MeOH) 4] 2 (Fe-BTT), a microporous solid with a BET surface area of 2010 m 2 g -1 and open Fe 2+ coordination sites. Hydrogen adsorption data collected at 77 K show a steep rise in the isotherm, associated with an initial isosteric heat of adsorption of 11.9 kJ mol -1, leading to a total storage capacity of 1.1 wt% and 8.4 g L -1 at 100 bar and 298 K. Powder neutron diffraction experiments performed at 4 K under various D 2 loadings enabled identification of ten different adsorption sites, with the strongest binding site residing just 2.17(5) Å from the framework Fe 2+ cation. Inelastic neutron scattering spectra are consistent with the strong rotational hindering of the H 2 molecules at low loadings, and further reveal the catalytic conversion of ortho-H 2 to para-H 2 by the paramagnetic iron centers. The exposed Fe 2+ cation sites within Fe-BTT also lead to the selective adsorption of CO 2 over N 2, with isotherms collected at 298 K indicating uptake ratios of 30.7 and 10.8 by weight at 0.1 and 1.0 bar, respectively. © The Royal Society of Chemistry 2011.
K. Sumida and S. Horike and S. S. Kaye and Z. R. Herm and W. L. Queen and C. M. Brown and F. Grandjean and G. J. Long and A. Dailly and J. R. Long, "Hydrogen Storage and Carbon Dioxide Capture in an Iron-based Sodalite-type Metal-organic Framework (Fe-BTT) Discovered via High-throughput Methods," Chemical Science, Royal Society of Chemistry, Jan 2010.
The definitive version is available at http://dx.doi.org/10.1039/c0sc00179a
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