A single precursor approach for ZIF synthesis: transformation of a new 1D [Zn(Im)(HIm)2(OAc)] structure to 3D Zn(Im)2 frameworks
The solvent free reaction of Zn(OAc)2 with an imidazole ligand resulted in a 1-dimensional (1D) chain structure with the formula [Zn(Im)(HIm)2(OAc)] (Im = imidazolate, HIm = imidazole, OAc = carboxylate) (1). The results by kinetic experiments suggest that (1) likely evolves from an unidentified metastable phase. This new 1D chain precursor (1) is a quaternary system comprising Zn, Im, OAc and HIm. We have used this 1D compound as a single precursor to prepare 3-dimensional (3D) Zn(Im)2 frameworks. Specifically, two Zn(Im)2 frameworks with known zni and coi topologies were prepared via thermal-mediated transformation when heated in an open atmosphere and in a closed vessel, respectively. In an open atmosphere, the kinetic experiments confirmed the rapid phase transformation from (1) to zni without formation of an intermediate phase. In contrast, in the formation process of coi in a closed vessel, phase transformation from (1) to zni and immediately from zni to coi was observed. Thus, in a closed vessel, the released molecules, HOAc and HIm, were occluded in the framework, which may together exert a cooperative structure-directing effect on the formation of the coi framework. Thus, a single precursor approach was established for the synthesis of ZIFs. The present work represents the first example of transforming a 1D coordination polymer into 3D ZIF framework structures.
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