Strong CO 2 Chemisorption in a Metal-Organic Framework with Proximate Zn-OH Groups.

A novel Zn benzotriazolate metal-organic framework (MOF), [Zn 9 (OAc) 6 (bbtm) 6 ] ( 1 , bbtm 2- = bis(benzotriazolyl)methanone, OAc - = acetate), has been synthesized and structurally characterized using micro-crystal electron diffraction. The framework contains 12-connected nonanuclear Zn clusters with Zn-OAc groups separated by short intercluster Zn···Zn distances of 6.06 Å. Postsynthetic OAc - /OH - ligand exchange followed by thermal activation generates 1a-OH , which adsorbs CO 2 at very low pressures (1.37 mmol/g at 2.5 mbar) and requires an unusually high desorption temperature (>160 °C). Diffuse reflectance IR Fourier transform spectroscopy (DRIFTS) and density functional theory (DFT) calculations have been used to interrogate the CO 2 binding mechanism in 1a-OH . The formation of unsymmetric bridging carbonate ligands within the Zn···Zn pockets accompanied by strong hydrogen bonding of the carbonate with a neighboring zinc aqua ligand explains the remarkably strong CO 2 affinity of 1a-OH .