Supramolecular templating agents and metal organic frameworks: control over crystal size and assembly.

Metal organic frameworks(MOFs) are an interesting class of microcrystalline materials constituted by metal ions or clusters connected by organic linkers characterised by their high porosity and tunable structures. Due to their chemical variability and numerous applications they have received great attention during the last few decades.Recently also the control of their physical form or macroscopic structure, such as crystal size, morphology and the aggregation of the crystals into superstructures, have received more attention since it would further develop and enhance properties and applications of these materials. Indeed beside all the inherent properties derived from the chemical composition and microporosity of MOFs the higher level of order or the control over the dimensionality or shape of the particles should enrich their overall performance and open new fields of application, such as drug delivery or integration into electronic sensor devices. In this context three prototypical MOFs were investigated, namely HKUST-­1, ZIF-­8 and ZIF-­61; at first an overview of the behavior of HKUST-­1 in presence of templating agents was performed, which involved the use of Pluronic-P123 (HO(CH2CH2O)20(CH2CH(CH3)O)70(CH2CH2O)20H, EO20PO70EO20, EO=ethylene oxide, PO=propylene oxide) and two carboxylic acids, namely octanoic acid and dodecanoic acid, on the synthesis of HKUST-­1. As a proof of concept, this chapter underlined the importance of the synthetic conditions and of the interactions between MOF precursors and templating agents in directing the macroscopic structure of the MOF Thereafter the directional self-­assembly properties of ZIF-­8 in aqueous media with the templating agents SPAN-­80 and/or dodecane for the formation of hollow capsule and colloidosomes was investigated, again in relation to optimize the synthetic conditions and understand the mechanism behind the hollow structure formation, which finally depended on the nature of the templating agent and the MOF precursors-­templating agent interactions. Furthermore the etching effect of imidazole on the hollow capsule, which led to flower-­like microcapsules was analyzed. Furthermore the optimization of the synthesis of zni phase in aqueous media and the topological and morphological conversion from zni phase (ZIF-­61) to sod phase (SALEM-­2) promoted by the surfactant SPAN-­80 was studied. The role of SPAN-­80 was further investigated also in light of the variation of the composition of the two ZIFs and the thermodynamic of the system. Finally the thesis was an attempt to rationalized the mechanism of MOF macroscopic structures formation, considering the structural features of the starting MOF, the synthetic conditions and the choice of the templating agents, envisioning a design a priori of the macroscopic structure of MOFs. <br/

Supramolecular templating of hierarchically porous metal–organic frameworks

This tutorial review summarises recent advances in the direct supramolecular templating of metal–organic frameworks (MOFs) with hierarchical porosity across the micro- and mesoporous regimes. These are set against the important synthetic considerations that need to be addressed to ensure that strong interactions between the MOF precursors and a stable template assembly allow the highest chance of success. The article is grouped by template type and each category is illustrated with key examples and, where reported, an evaluation of their enhanced properties arising from the hierarchical structuring of the porous networks

Pollen-like ZIF-8 colloidosomes via emulsion templating and etching

We report a one-pot emulsion-templating strategy for the preparation of ZIF-8 microcapsules both in the presence and absence of surfactants. Capsule diameter is tuneable in the range 1–10 μm, and they can be post-synthetically etched with excess imidazole to form hierarchical architectures resembling Oleaceae pollen grains