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).