Fig. 2: Depiction of the PCP structure.
From: Diffusion-rate sieving of propylene and propane mixtures in a cooperatively dynamic porous crystal
a The crystal structure of FDC–4a viewed along the b axis. Carbon, gray; nitrogen, blue; hydrogen, white; oxygen, red; copper, light blue. For clarity, the MODBAP moieties whose O atoms are uncoordinated with the OMSs of the Cu2+ paddle wheels are omitted. b The void in FDC–4a visualized by a small probe radius of 1.2 Å. The void volume is 1594 Å3 and corresponds to 12.3% of the unit-cell volume. The inner and outer surfaces of the pore are drawn in brown and yellow, respectively. The red arrow shows the helical pore. c The structure of the diffusion gate, which is surrounded by two H atoms on benzene rings of the two MODBAP moieties with a 3.76 Å distance. d Schematic diagram of the cooperatively dynamic PCP in this work. The PCP with one-dimensional (1D) transport pathways is constructed. The apertures are colored blue and red for the closed and open phases, respectively. In the closed phase, the pore entrances are smaller than the kinetic diameters of C3H8; hence, the pores are almost isolated, which regulates the diffusion of C3H8 by the thermal flipping of the gate moieties that slightly enlarge the gate (the apertures are colored green). In the open phase, the pore entrances become much larger because of the gate opening, and the pores open for C3H6 adsorption.
