Strong CO2 Binding in a Water-Stable, Triazolate-Bridged Metal−Organic Framework Functionalized with Ethylenediamine

• Published in: Journal of the American Chemical Society 2009-07, Vol.131 (25), p.8784-8786
• Main Authors: Demessence, Aude, D’Alessandro, Deanna M, Foo, Maw Lin, Long, Jeffrey R
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja903411w

Reaction of CuCl2·2H2O with 1,3,5-tris(1H-1,2,3-triazol-5-yl)benzene (H3BTTri) in DMF at 100 °C generates the metal−organic framework H3[(Cu4Cl)3(BTTri)8(DMF)12]·7DMF·76H2O (1-DMF). The sodalite-type structure of the framework consists of BTTri3−-linked [Cu4Cl]7+ square clusters in which each CuII center has a terminal DMF ligand directed toward the interior of a large pore. The framework exhibits a high thermal stability of up to 270 °C, as well as exceptional chemical stability in air, boiling water, and acidic media. Following exchange of the guest solvent and bound DMF molecules for methanol to give 1-MeOH, complete desolvation of the framework at 180 °C generated H3[(Cu4Cl)3(BTTri)8] (1) with exposed CuII sites on its surface. Following a previously reported protocol, ethylenediamine molecules were grafted onto these sites to afford 1-en, featuring terminal alkylamine groups. The N2 adsorption isotherms indicate a reduction in the BET surface area from 1770 to 345 m2/g following grafting. The H2 adsorption data at 77 K for 1 indicate a fully reversible uptake of 1.2 wt % at 1.2 bar, while the CO2 isotherm at 195 K shows a maximal uptake of 90 wt % at 1 bar. Compared to 1, the alkylamine-functionalized framework 1-en exhibits a higher uptake of CO2 at 298 K and pressures up to ca. 0.1 bar, as well as a higher CO2/N2 selectivity at all measured pressures. Significantly, 1-en also exhibits an isosteric heat of CO2 adsorption of 90 kJ/mol, which is much higher than the 21 kJ/mol observed for 1. This chemisorption interaction is the strongest reported to date for a metal−organic framework and points toward the potential utility of alkylamine-appended frameworks for the postcombustion capture of CO2 from low-pressure flue gas streams.