XRD patterns of NU-1000 and FeCN@NU-1000. The simulated XRD pattern of NU-1000 is also shown. For single crystal X-ray diffraction studies, larger NU-1000 crystals were grown from diethylformamide. These were then infiltrated and reacted with ferrocyanide in aqueous acid, as noted above. As shown in Figure , the installed Fe com-plexes are bound to the zirconium nodes and are sited exclusively in the c-pore, rather than the triangular or hexagonal channels/pores. (Note that the c-pores are geometrically orthogonal to the triangular and hexagonal channels and serve to interconnect them.) Closer inspection of the structure shows that attachment is achieved by Zr-oxo or Zr-hydroxo displacement of cyanide ligands on iron(II), rather than by Fe-CN displacement of node aqua ligands. Furthermore, two crystallographically independent Fe sites (Fe1 and Fe2) exist. Fe1 is linked to a pair of node-Zr ions via a pair of terminal hydroxo (or possibly oxo) ligands (see Figure ). Fe2 includes these links plus a third involving an oxygen anion linked to three node-Zr ions (see Fig- ).