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

Abstract

Reaction of CuCl(2) x 2 H(2)O with 1,3,5-tris(1H-1,2,3-triazol-5-yl)benzene (H(3)BTTri) in DMF at 100 degrees C generates the metal-organic framework H(3)[(Cu(4)Cl)(3)(BTTri)(8)(DMF)(12)] x 7 DMF x 76 H(2)O (1-DMF). The sodalite-type structure of the framework consists of BTTri(3-)-linked [Cu(4)Cl](7+) square clusters in which each Cu(II) 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 degrees 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 degrees C generated H(3)[(Cu(4)Cl)(3)(BTTri)(8)] (1) with exposed Cu(II) 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 N(2) adsorption isotherms indicate a reduction in the BET surface area from 1770 to 345 m(2)/g following grafting. The H(2) adsorption data at 77 K for 1 indicate a fully reversible uptake of 1.2 wt % at 1.2 bar, while the CO(2) 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 CO(2) at 298 K and pressures up to ca. 0.1 bar, as well as a higher CO(2)/N(2) selectivity at all measured pressures. Significantly, 1-en also exhibits an isosteric heat of CO(2) 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 CO(2) from low-pressure flue gas streams.