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Much has been written about the fundamental aspects of the metal–organic frameworks (MOFs). Still, details concerning the MOFs with structural flexibility are not comprehensively understood. However, a dramatic increase in research activities concerning rigid MOFs over the years has brought deeper levels of understanding for their properties and applications. Nonetheless, robustness and flexibility of such smart frameworks are intriguing for different research areas such as catalysis, adsorption, etc. This manuscript overviews the different aspects of framework flexibility. The review has touched lightly on several ideas and proposals, which have been demonstrated within the selected examples to provide a logical basis to obtain a fundamental understanding of their synthesis and behavior to external stimuli.

Surface modifications fundamentally influence the morphology of kaolinite nanostructures as a function of crystallinity and the presence of contaminants. Besides morphology, the catalytic properties of 1:1-type exfoliated aluminosilicates are also influenced by the presence of defect sites that can be generated in a controlled manner by mechanochemical activation. In this work, we investigated exfoliated halloysite nanoparticles with a quasi-homogeneous, scroll-type secondary structure toward developing structural/functional relationships for composition, atomic structure, and morphology. The surface properties of thin-walled nanoscrolls were studied as a function of mechanochemical activation expressed by the duration of dry-grinding. The surface characterizations were carried out using N, NH, and CO adsorption measurements. The effects of grinding on the nanohalloysite structure were followed using thermoanalytical thermogravimetric/derivative thermogravimetric (TG/DTG) and infrared spectroscopic [Fourier transform infrared/attenuated total reflection (FTIR/ATR)] techniques. Grinding results in partial dehydroxylation with similar changes as those observed for heat treatment above 300 °C. Mechanochemical activation shows a decrease in the dehydroxylation mass loss and the DTG peak temperature, a decrease in the specific surface area and the number of mesopores, an increase in the surface acidity, blue shift of surface hydroxide bands, and a decrease in the intensity of FTIR/ATR bands as a function of the grinding time. The experimental observations were used to guide atomic-scale structural and energetic simulations using realistic molecular cluster models for a nanohalloysite particle. A full potential energy surface description was developed for the mechanochemical activation and/or heating toward nanometahalloysite formation that aids the interpretation of experimental results. The calculated differences upon dehydroxylation show a remarkable agreement with the mass loss values from DTG measurements.

Heterogeneous copper catalysts were prepared by the deposition of CuI on a hybrid material consisting of silica and a polymer with imidazolium moieties.The solid materials were characterised using solid-phase NMR, Fourier transform infrared, Raman and X-ray photoelectron spectroscopies and Brunauer-Emmett-Teller measurements. The formation of copper-carbene complexes was proved from Raman spectra and the results were supported by density functional theory calculations. The catalyst could be recycled efficiently with low loss of copper. Metal leaching was proved to be facilitated by the use of conditions typical for a homogeneous system (the presence of a polar solvent or the addition of a tertiary amine). Besides simple model reactions, the best catalyst was found to be suitable for the synthesis of triazoles of more elaborate structure, such as ferrocene or steroid derivatives.

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