Effective CO2 and CO Separation Using [M2(DOBDC)](M=Mg, Co, Ni) with Unsaturated Metal Sites and Excavation of Their Adsorption Sites

Isostructural [M2(DOBDC)(EG)2] (M = Mg, Co, Ni) frameworks are first synthesized by controlling the pH* in the reaction medium. Coordinated ethylene glycols form a hexagonal OH cluster, which works as a template to grow single crystals with high crystallinity. After the liberation of solvated molecules, [M2(DOBDC)] shows notably higher surface areas than the reported values and completely different CO2 and CO separation properties depending on the kinds of unsaturated metal. Therefore, breakthrough experiments using a CO2/CO mixed gas show that Mg-MOF has a longer breakthrough time for CO2 than for CO, whereas Co/Ni-MOFs have longer breakthrough times for CO than for CO2. Apart from CO2 and CO, other gases such as CH4, H2, and N2 were almost not adsorbed at all in these materials at 298 K. To reveal the role of unsaturated metal sites, CO2 and CO adsorption sites are unequivocally determined by single-crystal X-ray diffraction analysis. One of very interesting discoveries is that there are two CO2 and CO ...