@SC-NU-1000. NU-1000 crystals suitable for single-crystal X-ray diffraction measurements (SC-NU-1000) were synthesized following the procedure reported in our recent study. After the final washing of the SC-NU-1000 with DMF, the crystals (~60 mg) were washed with water twice and transferred into a microwave vial. Thereafter, the solution containing potassium hexacyanoferrate(II) trihydrate was prepared following the procedure mentioned before and being added into the microwave vial. The exposure hexacyanoferrate(II) was conducted for 3 days with all the following washing steps similar to those for the synthesis of FeCN@NU-1000. After the final washing step with acetone, the obtained green crystals were washed with ethanol three times and then solvent-evacuated by using supercritical CO2 delivered by a Tousimis Samdri-PVT-3D (Rockville, MD) as described previously. The obtained crystals were further activated in an oven at 120 o C in air overnight, and the obtained sample was designated as FeCN@SC-NU-1000 for single-crystal X-ray diffraction measurements.