imidazolate

Imidazolate refers to the deprotonated form of imidazole, the monoanionic, five-membered N-heteroaromatic ring with formula C3N2H3−. The anion is produced by removing the N–H proton from imidazole, and its negative charge is delocalized over the ring, making the imidazolate a versatile ligand in coordination chemistry.

In metal complexes and metal–organic frameworks (MOFs), imidazolate commonly acts as a linker between metal centers. It can bridge two or more metals (μ2-bridging) and commonly coordinates through the ring nitrogens, though substitution and ring resonance allow various modes of binding. In zeolitic imidazolate frameworks (ZIFs), rigid imidazolate linkers connect transition-metal ions, often forming three-dimensional networks with porous structures. Linkers are frequently substituted (for example, 2-substituted imidazolates such as 2-methylimidazolate) to tune pore size, hydrophobicity, and chemical stability.

Synthesis and availability: Imidazolate ligands are typically generated in situ by deprotonation of imidazole derivatives using bases, followed by coordination to metals under solvothermal or hydrothermal conditions to yield MOFs or metal–imidazolate clusters.

Applications: Imidazolate-based MOFs, especially ZIFs, are widely studied for gas storage and separation (hydrogen, methane, CO2), catalysis, and sensing. Their robustness and thermal stability stem from strong M–N bonds and the rigid imidazolate linkers, imparting zeolite-like properties.