RESUMO
Postsynthetic modification methods have emerged as indispensable tools for tuning the properties and reactivity of metal-organic frameworks (MOFs). In particular, postsynthetic X-type ligand exchange (PXLE) at metal building units has gained increasing attention as a means of immobilizing guest species, modulating the reactivity of framework metal ions, and introducing new functional groups. The reaction of a Zn-OH functionalized analogue of CFA-1 (1-OH, Zn(ZnOH)4(bibta)3, where bibta2- = 5,5'-bibenzotriazolate) with organic substrates containing mildly acidic E-H groups (E = C, O, N) results in the formation of Zn-E species and water as a byproduct. This Brønsted acid-base PXLE reaction is compatible with substrates with pKa(DMSO) values as high as 30 and offers a rapid and convenient means of introducing new functional groups at Kuratwoski-type metal nodes. Gas adsorption and diffuse reflectance infrared Fourier transform spectroscopy experiments reveal that the anilide-exchanged MOFs 1-NHPh0.9 and 1-NHPh2.5 exhibit enhanced low-pressure CO2 adsorption compared to 1-OH as a result of a Zn-NHPh + CO2 â Zn-O2CNHPh chemisorption mechanism. The MFU-4l analogue 2-NHPh ([Zn5(OH)2.1(NHPh)1.9(btdd)3], where btdd2- = bis(1,2,3-triazolo)dibenzodioxin), shows a similar improvement in CO2 adsorption in comparison to the parent MOF containing only Zn-OH groups.
RESUMO
A Zn benzotriazolate metal-organic framework (MOF), [Zn(ZnO2CCH3)4(bibta)3] (1, bibta2- = 5,5'-bibenzotriazolate), has been subjected to a mild CH3CO2-/HCO3- ligand exchange procedure followed by thermal activation to generate nucleophilic Zn-OH groups that resemble the active site of α-carbonic anhydrase. The postsynthetically modified MOF, [Zn(ZnOH)4(bibta)3] (2*), exhibits excellent performance for trace CO2 capture and can be regenerated at mild temperatures. IR spectroscopic data and density functional theory (DFT) calculations reveal that intercluster hydrogen bonding interactions augment a Zn-OH/Zn-O2COH fixation mechanism.