Ultramicroporous MOF with High Concentration of Vacant CuII Sites

An ultrarnicroporous 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)(CONH2)(-)) 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 CO2 over CH4, 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 CO2 with the exposed metal sites.