Illuminating milling mechanochemistry by tandem real-time fluorescence emission and Raman spectroscopy monitoring.

In pursuit of accessible and interpretable methods for direct and real-time observation of mechanochemical reactions, we demonstrate a tandem spectroscopic method for monitoring of ball-milling transformations combining fluorescence emission and Raman spectroscopy, accompanied by high-level molecular and periodic density-functional theory (DFT) calculations, including periodic time-dependent (TD-DFT) modelling of solid-state fluorescence spectra. This proof-of-principle report presents this readily accessible dual-spectroscopy technique as capable of observing changes to the supramolecular structure of the model pharmaceutical system indometacin during mechanochemical polymorph transformation and cocrystallisation. The observed time-resolved spectroscopic and kinetic data are supported by X-ray diffraction and solid-state nuclear magnetic resonance spectroscopy measurements.

Modulating Thermal Properties of Polymers through Crystal Engineering.

Crystal engineering has exclusively focused on the development of advanced materials based on small organic molecules. We now demonstrate how the cocrystallization of a polymer yields a material with significantly enhanced thermal stability but equivalent mechanical flexibility. Isomorphous replacement of one of the cocrystal components enables the formation of solid solutions with melting points that can be readily fine-tuned over a usefully wide temperature range.

Toward Mechanistic Understanding of Mechanochemical Reactions Using Real-Time Monitoring.

The past two decades have witnessed a rapid emergence of interest in mechanochemistry-chemical and materials reactivity achieved or sustained by the action of mechanical force-which has led to application of mechanochemistry to almost all areas of modern chemical and materials synthesis: from organic, inorganic, and organometallic chemistry to enzymatic reactions, formation of metal-organic frameworks, hybrid perovskites, and nanoparticle-based materials. The recent success of mechanochemistry by ball milling has also raised questions about the underlying mechanisms and has led to the realization that the rational development and effective harnessing of mechanochemical reactivity for cleaner and more efficient chemical manufacturing will critically depend on establishing a mechanistic understanding of these reactions. Despite their long history, the development of such a knowledge framework for mechanochemical reactions is still incomplete.

Challenging the Ostwald rule of stages in mechanochemical cocrystallisation.

Mechanochemistry provides an efficient, but still poorly understood route to synthesize and screen for polymorphs of organic solids. We present a hitherto unexplored effect of the milling assembly on the polymorphic outcome of mechanochemical cocrystallisation, tentatively related to the efficiency of mechanical energy transfer to the milled sample. Previous work on mechanochemical cocrystallisation has established that introducing liquid or polymer additives to milling systems can be used to direct polymorphic behavior, leading to extensive studies how the amount and nature of grinding additive affect reaction outcome and polymorphism.

Understanding disorder and linker deficiency in porphyrinic zirconium-based metal-organic frameworks by resolving the ZrO cluster conundrum in PCN-221.

Porphyrin-based metal-organic frameworks (MOFs), exemplified by MOF-525, PCN-221, and PCN-224, are promising systems for catalysis, optoelectronics, and solar energy conversion. However, subtle differences between synthetic protocols for these three MOFs give rise to vast discrepancies in purported product outcomes and description of framework topologies. Here, based on a comprehensive synthetic and structural analysis spanning local and long-range length scales, we show that PCN-221 consists of ZrO(OH) clusters in four distinct orientations within the unit cell, rather than ZrO clusters as originally published, and linker vacancies at levels of around 50%, which may form in a locally correlated manner.

Monitoring polymer-assisted mechanochemical cocrystallisation through in situ X-ray powder diffraction.

Time-resolved mechanochemical cocrystallisation studies have so-far focused solely on neat and liquid-assisted grinding. Here, we report the investigation of polymer-assisted grinding reactions using in situ X-ray powder diffraction, revealing that reaction rate is almost double compared to neat grinding and independent of the molecular weight and amount of the polymer additive used.

monitoring of mechanochemical synthesis of calcium urea phosphate fertilizer cocrystal reveals highly effective water-based autocatalysis.

Using the mechanosynthesis of the calcium urea phosphate fertilizer cocrystal as a model, we provide a quantitative investigation of chemical autocatalysis in a mechanochemical reaction. The application of Raman spectroscopy and synchrotron X-ray powder diffraction to monitor the reaction of urea phosphate and either calcium hydroxide or carbonate enabled the first quantitative and study of a mechanochemical system in which one of the products of a chemical reaction (water) mediates the rate of transformation and underpins positive feedback kinetics. The herein observed autocatalysis by water generated in the reaction enables reaction acceleration at amounts that are up to 3 orders of magnitude smaller than in a typical liquid-assisted mechanochemical reaction.

Controlling the Polymorphism and Topology Transformation in Porphyrinic Zirconium Metal-Organic Frameworks via Mechanochemistry.

Tetratopic porphyrin-based metal-organic frameworks (MOFs) represent a particularly interesting subclass of zirconium MOFs due to the occurrence of several divergent topologies. Control over the target topology is a demanding task, and reports often show products containing phase contamination. We demonstrate how mechanochemistry can be exploited for controlling the polymorphism in 12-coordinated porphyrinic zirconium MOFs, obtaining pure hexagonal PCN-223 and cubic MOF-525 phases in 20-60 min of milling.

Green and rapid mechanosynthesis of high-porosity NU- and UiO-type metal-organic frameworks.

The use of a dodecanuclear zirconium acetate cluster as a precursor enables the rapid, clean mechanochemical synthesis of high-microporosity metal-organic frameworks NU-901 and UiO-67, with surface areas up to 2250 m2 g-1. Real-time X-ray diffraction monitoring reveals that mechanochemical reactions involving the conventional hexanuclear zirconium methacrylate precursor are hindered by the formation of an inert intermediate, which does not appear when using the dodecanuclear acetate cluster as a reactant.

Structures, Thermodynamic Relations, and Magnetism of Stable and Metastable Ni(NCS) Coordination Polymers.

Reaction of Ni(NCS) with 4-aminopyridine in different solvents leads to the formation of compounds with the compositions Ni(NCS)(4-aminopyridine) (1), Ni(NCS)(4-aminopyridine)(HO) (2), [Ni(NCS)(4-aminopyridine)(MeCN)]·MeCN (3), and [Ni(NCS)(4-aminopyridine)] (5-LT). Compounds 1, 2, and 3 form discrete complexes, with octahedral metal coordination. In 5-LT the Ni cations are linked by single thiocyanate anions into chains, which are further connected into layers by half of the 4-aminopyridine coligands.

Synthesis, structures, magnetic, and theoretical investigations of layered Co and Ni thiocyanate coordination polymers.

Reaction of cobalt(ii) and nickel(ii) thiocyanate with ethylisonicotinate leads to the formation of [M(NCS)(ethylisonicotinate)] with M = Co (2-Co) and M = Ni (2-Ni), which can also be obtained by thermal decomposition of M(NCS)(ethylisonicotinate) (M = Co (1-Co), Ni (1-Ni)). The crystal structure of 2-Ni was determined by single crystal X-ray diffraction. The Ni(ii) cations are octahedrally coordinated by two N and two S bonding thiocyanate anions and two ethylisonicotinate ligands and are linked by pairs of anionic ligands into dimers, that are connected into layers by single thiocyanate bridges.

In Situ Monitoring and Mechanism of the Mechanochemical Formation of a Microporous MOF-74 Framework.

Mechanochemistry provides a rapid, efficient route to metal-organic framework Zn-MOF-74 directly from a metal oxide and without bulk solvent. In situ synchrotron X-ray diffraction monitoring of the reaction course reveals two new phases and an unusual stepwise process in which a close-packed intermediate reacts to form the open framework. The reaction can be performed on a gram scale to yield a highly porous material after activation.

Solid-State Reversible Nucleophilic Addition in a Highly Flexible MOF.

A flexible and porous metal-organic framework, based on Co(II) connectors and benzotriazolide-5-carboxylato linkers, is shown to selectively react with guest molecules trapped in the channels during the sample preparation or after an exchange process. Stimulated by a small crystal shrinking, upon compression or cooling, the system undergoes a reversible, nonoxidative nucleophilic addition of the guest molecules to the metal ion. With dimethylformamide, only part of the penta-coordinated Co atoms transform into hexa-coordinated, whereas with the smaller methanol all of them stepwise increase their coordination, preserving the crystallinity of the solid at all stages.