Installation of cyano-ferrate(II) species in NU-1000 was conducted in an acidic aqueous solution in an air-free and dark environment, as described in the experimental section. (Thus, we capitalize on the known stability of Zr-MOFs in noncoordinating aqueous acid. ) Following solvent exchange and, for single-crystal X-ray measurements, treatment with supercritical CO2, the isolated material was heated under vacuum at 120 o C; again see the experimental section for details. The obtained material showing a brown color is designated as "FeCN@NU-1000". The powder X-ray diffraction (PXRD) pattern of FeCN@NU-1000 reveals the same diffraction peaks as those appearing in both the experimental and simulated patterns of NU-1000, implying that crystallinity is largely retained and that the gross structure of the framework is unchanged. Scanning electron microscopy (SEM) of microcrystals of FeCN@NU-1000 shows a rod-shape morphology, which unchanged from that for unmodified NU-1000 (Figure ). Energy dispersive X-ray spectroscopy (EDS) line-scan measurements of individual crystallites indicate both iron and nitrogen are uniformly distributed within each crystallite (Figure ). Inductively coupled plasma optical emission spectrometry (ICP-OES) measurements show that there, on average, 1.1 iron atoms, per hexa-zirconium node.