Ultramicroporous MOF with High Concentration of Vacant Cu^II Sites

An ultramicroporous metal–organic framework (MOF) is reported that contains 0.35 nm nanotube-like channels with an unprecedented concentration of vacant Cu II coordination sites. The nonintersecting, narrow channels in [Cu 3 (cdm) 4 ] (cdm = C(CN) 2 (CONH 2 ) − ) align in two perpendicular directions, structurally resembling copper-doped carbon nanotubes with Cu II embedded in the walls of the channels. The combination of ultramicroporosity with the exposed Cu II coordination sites gives size-based selectivity of CO 2 over CH 4, based on pore-size distribution and modeling. Neutron powder diffraction and molecular dynamics simulations show the close packing of single rows of guests within the tubular nanostructure and interaction of CO 2 with the exposed metal sites.