Systematic Investigation of CO2 Adsorption Energetics in Metal-Organic Frameworks Based on Imidazolyl Linkers

This study explores system dependence (from the choice of metal and ligand) in the energetics for CO2 confinement in 3-dimensional (3D) metal-organic frameworks (MOFs) employing imidazolyl ligands, namely, ditopic 2-methylimidazole (HMeIm) in Zn(MeIm)(2) (ZIF-8), Co(MeIm)(2) (ZIF-67), and tetratopic tetrakis(imidazolyl) boric acid (HB(MeIm)4) in CuB-(MeIm)(4) (Cu-BIF-3). All frameworks have a sodalite topology. Direct gas adsorption calorimetric experiments enable quantitation of energetic drive for CO2 confinement in the frameworks. The general trend in the integral adsorption enthalpy Delta H-int (kJ/mol) is Cu-BIF-3 > ZIF-8 > ZIF-67. In ZIFs, greater porosity is consistent with more favorable CO2 incorporation. Overall, the use of larger linkers in BIFs provides the greatest enhancement of the energetics of CO2 adsorption in MOFs. The strength of guest-host interactions depends strongly on the choice of linker and metal.