Abstract
A previously unknown solid phase in the zinc-imidazole system relevant for the synthesis of ZIF-8 was obtained by adding a small excess of methylimidazole (Hmim) to a diluted zinc chloride solution...
Highlights
A large subgroup of metal−organic frameworks (MOFs) called zeolitic imidazolate frameworks (ZIFs)[1] or metal-azolate frameworks (MAFs)[2] has been studied thoroughly since its discovery more than ten years ago
We present the synthesis of a previously unknown ZIF-compound, Zn3(mim)5ClH2O·xH2O with x = 0.74 that we tentatively denote as “ZIF-yqt hydrate” by the use of an aqueous, low concentrated zinc chloride solution
While constant ratios of Zn:Hmim at different concentrations yield the same product, a higher amount of Hmim leads to the formation of ZIF-8dia
Summary
A large subgroup of metal−organic frameworks (MOFs) called zeolitic imidazolate frameworks (ZIFs)[1] or metal-azolate frameworks (MAFs)[2] has been studied thoroughly since its discovery more than ten years ago. The removal of both coordinated and noncoordinated water from ZIF-yqt hydrate leads to the formation of Zn3(mim)5Cl = ZIF-yqt anhydrous that is associated with a structural transition indicated by a significant change of the XRPD pattern (Figure 7a,b). Both ZIF compounds crystallize in the same space group, but the metric of the unit cell differs (Supporting Information, Table S2). 451 s (7.5 min) and the ZIF-yqt hydrate related (200) reflection is observed again (Figure 11, green and blue patterns) Both the release of noncoordinated and coordinated water and the structural transition that is connected with the dehydration is reversible. At higher concentrations of methylimidazole, chloride is replaced, which leads to the formation of ZIF-8 or ZIF8dia.[26,27] For the use of zinc nitrate as the precursor, a similar compound is reported, but the crystal structure has not been determined yet.[23,47,48]
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