metallimidazolate

Metallimidazolate refers to coordination compounds and extended materials in which metal ions are linked by imidazolate ligands, derivatives of imidazole that have been deprotonated. The term covers discrete metal-imidazolate complexes as well as metal-organic frameworks in which imidazolate or substituted imidazolate ligands bridge metal centers, forming one-, two-, or three-dimensional networks. The imidazolate linker is known for its strong M–N bonds and for promoting tetrahedral or octahedral metal coordination geometries, leading to robust frameworks.

Common metals include Zn2+, Co2+, Cu2+, Fe3+, Ni2+ and others; the most famous class is zeolitic imidazolate frameworks (ZIFs), exemplified by ZIF-8, where zinc ions are connected by 2-methylimidazolate to give a porous 3D framework.

Synthesis typically involves solvothermal or hydrothermal reactions of metal salts with imidazole or imidazolate derivatives in polar solvents such as DMF or water, often at moderate temperatures. Modulators and substitutions on the imidazole ring can influence crystallinity, topology, and pore size. Ball-milling and other green methods have also been reported.

Properties of metallimidazolates include high thermal and chemical stability, tunable porosity, and adjustable hydrophilicity or hydrophobicity. They frequently exhibit high surface areas and well-defined pore structures, making them suitable for gas storage (e.g., hydrogen, carbon dioxide), separations, catalysis, sensing, and even drug delivery in some cases.

See also: metal-organic framework, zeolitic imidazolate framework, imidazole, coordination polymer.