Magnesium imidazolate – a first porous zeolitic imidazolate framework with alkali and alkaline earth metals

Zeolitic imidazolate frameworks (ZIFs) are an outstanding class of MOFs, constructed from tetrahedrally configured transition metal cations linked through bridging imidazolate (Im) spacers.ZIFs are structurally isiomorphic to zeolites since the metal-Im-metal angle is similar to the Si-O-Si angle (145°) in the latter compounds.This feature was exploited to produce a huge variety of porous transition metal-based ZIFs.Our initial goal was to combine Im and alkali metal borohydrides in the same structure with the formation of porous borohydride compounds, where Im serves as a structural unit of the framework, while borohydride anions provide with a functionality.However, alkali and alkaline earth metal-based imidazolates are not structurally characterized so far.Thus, the coordination chemistry of Im towards alkali and alkaline earth metal cations remains a challenge.With this in mind and inspired by the storage properties of ZIFs, we have recently turned our attention to Im-based coordination compounds with Li + , Na + and K + [1].Unfortunately, these imidazolates form dense and hypercoordinated structures.The coordinative demand of the metal cation increases with an increase of the ionic radii.The Li + cation exhibits a strong propensity to form heteroleptic structures, while the K + cation allows to coordinate the Im ring through the π-system.Our next challenge was to obtain magnesium imidazolate (MgIm 2 ), which, based on the nature of Mg 2+ as well as its coordination chemistry, was considered as a much more promising complexing agent in comparison with alkali metal cations.While, the freshly synthesized MgIm 2 was found to be amorphous, annealing at relatively high temperatures yields the crystalline and porous MgIm 2 .Herein, we present our results on the synthesis, characterization and some properties of newly obtained MgIm 2 .