Preferential CO2 adsorption and theoretical simulation of a Cu(II)-based metal-organic framework with open-metal sites and basic groups

By utilizing the 1,3,5-benzenetricarboxylic acid (H(3)btc) and the N-rich melamine (ma) as the co-ligands, a new microporous cluster-based metal-organic framework [Cu-3(btc)(2)(ma)(H2O)(2)] (DMA)(4) (1) containing open metal sites and uncoordinated nitrogen atoms on the internal surface was solvothermally synthesized. The single crystal X-ray study reveals that compound 1 is built up from the {Cu-3(ma)(COO)(6)(H2O)(2)} cluster-based secondary building unit (SBU) and incorporates two types of polyhedral cages in the framework, which results in 1D nanosized channels along the c axis. More importantly, the activated compound 1 exhibits not only high uptake capacity for CO2 molecules at room temperature but also a significant selective adsorption of CO2 over CH4, which may be ascribed to the proper-sized pores with high density of open metal sites as well as the amine and triazine decorated pore surroundings. Meanwhile, the Grand Canonical Monte Carlo (GCMC) simulations on CO2 adsorption of compound 1 demonstrate that the both of the open metal sites and melamine backbone play key roles in the CO2 binding.