Solvent-Free Synthesis of ZIFs: A Route toward the Elusive Fe(II) Analogue of ZIF‑8

Herein we report the synthesis of an elusive metal–organic framework, the iron­(II) analogue of ZIF-8 with the formula Fe­(2-methylimidazolate)2, here denoted as MUV-3. The preparation of this highly interesting porous material, inaccessible by common synthetic procedures, occurs in a solvent-free reaction upon addition of an easily detachable template molecule, yielding single crystals of MUV-3. This methodology can be extended to other metals and imidazolate derivatives, allowing the preparation of ZIF-8, ZIF-67, and the unprecedented iron­(II) ZIFs Fe­(2-ethylimidazolate)2 and Fe­(2-methylbenzimidazolate)2. The different performance of MUV-3 toward NO sorption, in comparison to ZIF-8, results from the chemisorption of NO molecules, which also causes a gate-opening behavior. Finally, the controlled pyrolysis of MUV-3 results in a N-doped graphitic nanocomposite that exhibits extraordinary performance for the oxygen evolution reaction (OER), with low overpotential at different current densities (316 mV at 10 mA cm–2), low Tafel slope (37 mV per decade), high maximum current density (710 mA cm–2 at 2.0 V vs RHE), and great durability (15 h).