Solvent-Free Synthesis of ZIFs Compatible with Iron: A Route Towards 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 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 is extensive to other metals and imidazolate derivatives, allowing the preparation of ZIF-8, ZIF-67 and other unprecedented iron(II) ZIFs, Fe(2-ethylimidazolate)2 and Fe(2-methylbenzimidazolate)2. The different performance of MUV-3 towards NO sorption, compared 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 performances for 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 large durability (15 h).