Surfactant-directed syntheses of mesostructured zinc imidazolates: formation mechanism and structural insights

Abstract

Supramolecular templating techniques have been widely used to direct the formation of porous materials with the goal of introducing permanent mesoporosity. While surfactant-directed self-assembly has been exploited for inorganic materials such as titania, silica, organosilica, and zeolites, it has rarely been applied to metal-organic frameworks (MOFs) and coordination polymers. Here we introduce a new family of gemini surfactant-directed zinc imidazolates, referred to as mesostructured imidazolate frameworks (MIFs), and present a detailed study on the influence of different gemini-type surfactants on the formation mechanism and structures of the resulting zinc imidazolates. 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 also 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. Solid-state 2D 13 C{ 1 H} HETCOR NMR measurements on prototypic CTAB-directed MIF-1 establish that the head group moieties of the surfactant molecules interact strongly with the zinc-imidazolate-bromide sheets. Additionally, the 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.

Multi-scale crystal engineering of metal organic frameworks

“…Similar rod-like morphologies have been obtained by Taylor et al [237,238] in reverse microemulsion systems for other metal-organic frameworks, such as In this latter case the microemulsion system was composed of CTAB as cationic surfactant, isooctane as the 'oil' phase, 1-hexanol as co-surfactant and water [26]. This approach was further extended to other coordination polymers by Lotsch and co-workers [235,239], who synthesized coordination polymer nanosheets composed of Zn, benzimidazole and acetate. In this case lamellar reverse microemulsions were prepared with CTAB, heptane, 1-hexanol and water and were used to confine the MOF growth into the interlamellar space.…”

Surfactant-Templating of Zeolites: From Design to Application

“…In the particular, the application of surfactant-oriented strategies for the development of mesopororous zinc imidazolate frameworks (ZIFs) have recently proven successful. [138] Those structures are especially interesting, as some of their structural types are isomorphic to zeolite structures.…”

Influence of octanohydroxamic acid on the association behavior of cationic surfactants: Hydrolytic cleavage of phosphate ester

“…In recent years, the application of surfactants has a robust transition in both academic and industrial research [6][7]. These application areas include the use of surfactants as non-viral vectors for gene delivery [8], anti-fungal agents [9], drug delivery agents [10], as well as anti-microbial agents [11]. The physiochemical properties of surfactants viz.…”