Post-Synthetic Cyano-ferrate(II) Functionalization of a Metal-Organic Framework, NU-1000

Starting with ferrocyanide ions in acidic aqueous solution, cyano-ferrate(II) species are post-synthetically grafted to the nodes of a mesoporous zirconium-based MOF, NU-1000. As indicated by single-crystal X-ray crystallography, grafting occurs by substitution of cyanide ligands by node-based hydroxo and oxo ligands rather than by substitution of node aqua ligands by cyanide ligands as bridges between Fe(II) and Zr(IV). The installed moieties yield a broad absorption band that is tentatively ascribed to iron-to-zirconium charge transfer. Consistent with Fe(III/II) redox activity, a modest fraction of the installed iron complexes are directly electrochemically addressable.