Chemical Conversion of Linkages in Covalent Organic Frameworks

The imine linkages of two layered, porous covalent organic frameworks (COFs), TPB-TP-COF ([C₆H₃(C₆H₄N)₃]₂[C₆H₄(CH)₂]₃, <b>1</b>) and 4PE-1P-COF ([C₂(C₆H₄N)₄]­[C₆H₄(CH)₂]₂, <b>2</b>), have been transformed into amide linkages to make the respective isostructural amide COFs <b>1′</b> and <b>2′</b> by direct oxidation with retention of crystallinity and permanent porosity. Remarkably, the oxidation of both imine COFs is complete, as assessed by FT-IR and ¹³C CP-MAS NMR spectroscopy and demonstrates (a) the first chemical conversion of a COF linkage and (b) how the usual “crystallization problem” encountered in COF chemistry can be bypassed to access COFs, such as these amides, that are typically thought to be difficult to obtain by the usual de novo methods. The amide COFs show improved chemical stability relative to their imine progenitors

The Chemistry of CO₂ Capture in an Amine-Functionalized Metal–Organic Framework under Dry and Humid Conditions

The use of two primary alkylamine functionalities covalently tethered to the linkers of IRMOF-74-III results in a material that can uptake CO₂ at low pressures through a chemisorption mechanism. In contrast to other primary amine-functionalized solid adsorbents that uptake CO₂ primarily as ammonium carbamates, we observe using solid state NMR that the major chemisorption product for this material is carbamic acid. The equilibrium of reaction products also shifts to ammonium carbamate when water vapor is present; a new finding that has impact on control of the chemistry of CO₂ capture in MOF materials and one that highlights the importance of geometric constraints and the mediating role of water within the pores of MOFs