Giulio I. Lampronti

Phase Transitions in Zeolitic Imidazolate Framework 7: The Importance of Framework Flexibility and Guest-Induced Instability

Zeolite-related materials exhibit a range of novel properties and are of considerable interest for their potential engineering applications. Zeolitic imidazolate frameworks (ZIFs) display zeolite-type structures and are constructed by transitional metals and imidazole molecules.(1) With a wide variety of potential organic ligands, ZIFs present a new family of possible zeolite-related structures with tunable and functionalizable properties. Because of the coordinative metal–imidazolate bonding forming their frameworks, ZIFs are commonly more flexible than their aluminosilicate analogues. They also show unusual gas sorption capacity and related properties. Due to their framework flexibility, ZIFs can undergo structural transformations, e.g., during the sorption process(2) or under high temperature(3) or pressure.(4) It is of great significance to understand potential structural phase transitions since they strongly affect ZIFs’ structurally-related sorption and mechanical properties, which are essential to ZIFs-based technology innovations and industrial applications.Zeolite-related materials exhibit a range of novel properties and are of considerable interest for their potential engineering applications. Zeolitic imidazolate frameworks (ZIFs) display zeolite-type structures and are constructed by transitional metals and imidazole molecules.(1) With a wide variety of potential organic ligands, ZIFs present a new family of possible zeolite-related structures with tunable and functionalizable properties. Because of the coordinative metal–imidazolate bonding forming their frameworks, ZIFs are commonly more flexible than their aluminosilicate analogues. They also show unusual gas sorption capacity and related properties. Due to their framework flexibility, ZIFs can undergo structural transformations, e.g., during the sorption process(2) or under high temperature(3) or pressure.(4) It is of great significance to understand potential structural phase transitions since they strongly affect ZIFs’ structurally-related sorption and mechanical properties, which are essential to ZIFs-based technology innovations and industrial applications.

Melt-Quenched Glasses of Metal-Organic Frameworks

Crystalline solids dominate the field of metal-organic frameworks (MOFs), with access to the liquid and glass states of matter usually prohibited by relatively low temperatures of thermal decomposition. In this work, we give due consideration to framework chemistry and topology to expand the phenomenon of the melting of 3D MOFs, linking crystal chemistry to framework melting temperature and kinetic fragility of the glass-forming liquids. Here we show that melting temperatures can be lowered by altering the chemistry of the crystalline MOF state, which provides a route to facilitate the melting of other MOFs. The glasses formed upon vitrification are chemically and structurally distinct from the three other existing categories of melt-quenched glasses (inorganic nonmetallic, organic, and metallic), and retain the basic metal-ligand connectivity of crystalline MOFs, which connects their mechanical properties to their starting chemical composition. The transfer of functionality from crystal to glass points toward new routes to tunable, functional hybrid glasses.

Supramolecular metathesis: co-former exchange in co-crystals of pyrazine with (R,R)-, (S,S)-, (R,S)- and (S,S/R,R)-tartaric acid

Co-crystals of dextro-(R,R), levo-(S,S), meso-(R,S) and racemic (R,R–S,S)-tartaric acid with pyrazine were obtained by manual kneading and slurry experiments; subsequent reactions in the solid state between these co-crystals and the various forms of tartaric acid in the solid state and via slurry show that co-former exchange takes place according to the sequence of stability [(R,S)-ta]2·py > (S,S/R,R)-ta·py > (R,R)-ta·py or (S,S)-ta·py.

Direct visualisation of carbon dioxide adsorption in gate-opening zeolitic imidazolate framework ZIF-7

The crystal structures of zeolitic imidazolate framework 7 (ZIF-7) under various CO2 pressures were studied by high-resolution neutron powder diffraction. CO2 adsorption in ZIF-7 is visualised and demonstrated to be primarily controlled by the benzimidazolate ligands via a gate-opening mechanism. Our results highlight the importance of pressure on the CO2 adsorption and the related structural framework responses in ZIF-7.

Direct Observation of Intermediates in a Thermodynamically Controlled Solid-State Dynamic Covalent Reaction

We present the first polymorph interconversion study that uses solid-state dynamic covalent chemistry (DCC). This system exhibits unexpected and rich behavior, including the observation that under appropriate conditions the polymorph interconversion of a heterodimer proceeds through reversible covalent chemistry intermediates, and this route is facilitated by one of the two disulfide homodimers involved in the reaction. Furthermore, we demonstrate experimentally that in all cases a dynamic equilibrium is reached, meaning that changing the milling conditions affects the free energy difference between the two polymorphs and thus their relative stability. We suggest that this effect is due to the surface solvation energy combined with the high surface to volume ratio of the nanocrystalline powder.

Calixarene Assisted Rapid Synthesis of Silver-Graphene Nanocomposites with Enhanced Antibacterial Activity

Demonstrated herein is a single rapid approach employed for synthesis of Ag-graphene nanocomposites, with excellent antibacterial properties and low cytotoxicity, by utilizing a continuous hydrothermal flow synthesis (CHFS) process in combination with p-hexasulfonic acid calix[6]arene (SCX6) as an effective particle stabilizer. The nanocomposites showed high activity against E. coli (Gram-negative) and S. aureus (Gram-positive) bacteria. The materials were characterized using a range of techniques including transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, UV-vis spectrophotometry, FT-IR, and X-ray powder diffraction (XRD). This rapid, single step synthetic approach not only provides a facile means of enabling and controlling graphene reduction (under alkaline conditions) but also offers an optimal route for homogeneously producing and depositing highly crystalline Ag nanostructures into reduced graphene oxide substrate.

Structure determination of novel ionic co-crystals from powder data: the use of rigid fragments in simulated annealing algorithms

A new approach is presented here for the structural solution of anhydrous and hydrated metal–organic coordination compounds of alkali and alkaline earth metals by using rigid structure fragments in combination with simulated annealing algorithms. We empirically show how this approach minimizes computation time, while allowing us to obtain the correct result. The structures of two novel ionic co-crystals have been solved from powder data with this approach.

Mechanochemical preparation of adducts (co-crystals and molecular salts) of 1,4-diazabicyclo-[2.2.2]-octane with aromatic polycarboxylic acids

Solid-state adducts (co-crystals and molecular salts) of 1,4-diazabicyclo-[2.2.2]-octane (DABCO) with aromatic polycarboxylic acids (isophthalic acid, isoH2, dinicotinic acid, dinH2 and dipicolinic acid, dipH2) were prepared in the solid state by grinding and kneading techniques, and fully characterized via X-ray diffraction. The polycarboxylic acids differ for the presence/absence and position of a nitrogen atom in the aromatic ring; the extent of proton transfer, from the carboxylic groups on the acids to the nitrogen atoms on DABCO, reflects the trend of solution acidity of the three polycarboxylic acids.

Fermi liquid breakdown and evidence for superconductivity in YFe2Ge2

In the d-electron system YFe2Ge2, an unusually high and temperature dependent Sommerfeld ratio of the specific heat capacity C /T ∼ 100 mJ/(mol K2) and an anomalous power law temperature dependence of the electrical resistivity signal Fermi liquid breakdown, probably connected to a close-by quantum critical point. Full resistive transitions and DC diamagnetic screening fractions of up to 80% suggest that pure samples of YFe2Ge2 superconduct below 1.8 K. (© 2014 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

Selective calixarene directed synthesis of MXene plates, crumpled sheets, spheres and scrolls

Fully exploiting the electronic and mechanical properties of 2D laminar materials not only requires efficient and effective means of their exfoliation into low dimensional layers, but also necessitates a means of changing their morphology so as to explore any enhancement that this may offer. MXenes are a rapidly emerging new class of such laminar materials with unique properties. However, access to other morphologies of MXenes has not yet been fully realised. To this end we have developed the synthesis of MXenes (Ti2 C) as plates, crumpled sheets, spheres and scrolls, which involves selective intercalation of p-phosphonic calix[n]arenes, with control in morphology arising from the choice of the size of the macrocycle, n=4, 5, 6, or 8. This opens up wider avenues of discovery/design for new morphologies from the wider family of MXenes beyond Ti2 C, along with opportunities to exploit any new physico-chemical properties proffered.