Abstract
A detailed study on the formation mechanism, local and long-range structures of surfactant-directed lamellar zinc imidazolates is presented.
Highlights
While exploring synthetic approaches to hierarchical zinc imidazolate framework (ZIF) by soft templating, we have recently discovered the class of mesostructured imidazolate frameworks (MIFs), which combine structural elements of both coordination polymers and liquid crystalline mesophases to form hierarchical structures ordered on both the atomic- and nanoscale.[20]
The proposed formation mechanism for MIF-type materials involves co-assembly and crystallization processes that yield lamellar mesostructured imidazolate frameworks. Understanding and controlling such processes has implications for the syntheses of microporous zinc imidazolate framework (ZIF) materials, whose formation can be suppressed in surfactant-rich solutions, whereas formation of MIF materials is favored in the presence of surfactants and triggered by the addition of halogenides
The nuclear magnetic resonance (NMR) analyses suggest that MIF-1 has a significant fraction of surfactant molecules that are interdigitated between the zinc-imidazolate-bromide sheets with an antiparallel stacking arrangement, consistent with the high thermal and chemical stability of the MIF hybrid materials
Summary
While exploring synthetic approaches to hierarchical ZIFs by soft templating, we have recently discovered the class of mesostructured imidazolate frameworks (MIFs), which combine structural elements of both coordination polymers and liquid crystalline mesophases to form hierarchical structures ordered on both the atomic- and nanoscale.[20]. Ryoo et al reported the synthesis of a hierarchically nanoand mesoporous MFI zeolite, where gemini-type surfactants directed the formation of MFI nanosheets with a multilamellar structure.[22,23,24] Gemini surfactants can be described by the general structure n–m–n, with n being a terminal aliphatic carbon chain and m being a linker between two quaternary nitrogen ions (Fig. 1b) Surfactant properties such as packing parameter and critical micelle concentration, which determine the micellar curvature, are a function of the size, geometry and charge density of the gemini surfactant molecules.[25,26,27,28] Earlier work on the influence of these surfactants on the formation of periodic mesoporous organosilica (PMO) has shown that n–6–n gemini surfactants (n = 12–22) can form multiple mesostructures, depending on the length of the terminal carbon chains. The detailed insights provided by this work are expected to aid in the design of MIFs with a broader range of mesostructured compositions, topologies, and hierarchical structural ordering
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