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).