Highlighting the Cobalt Selective Precipitation Mechanism of Imidazole Linkers into a Multimetallic Solution (Ni, Co, and Mn)

Imidazolate linkers selectively precipitate in pure cobalt-based hybrid materials [zeolitic-imidazolate-frameworks (ZIFs)] when they are directly added in solutions containing nickel, manganese, and cobalt. The favored reactivity of imidazole against cobalt versus other cations is deeply studied, and selectivity mechanisms are explained, thanks to experimental data supported by DFT calculations. The preferential coordination of imidazole with cobalt instead of nickel cations is explained, thanks to the tetrahedral Co(Im)₄ cluster formation, which is the main building block of ZIF structures. On the other hand, the cobalt/manganese selectivity is kinetically driven. Different ligands from the imidazole family have been compared, and a direct correlation between cobalt/manganese selectivity and pK_a of molecules has been highlighted.