Time resolved in situ (TRIS) monitoring has revolutionised the study of mechanochemical transformations but has been limited by available data quality. Here we report how a combination of miniaturised grinding jars together with innovations in X-ray powder diffraction data collection and state-of-the-art analysis strategies transform the power of TRIS synchrotron mechanochemical experiments. Accurate phase compositions, comparable to those obtained by ex situ measurements, can be obtained with small sample loadings. Moreover, microstructural parameters (crystal size and microstrain) can be also determined with high confidence. This strategy applies to all chemistries, is readily implemented, and yields high-quality diffraction data even using a low energy synchrotron source. This offers a direct avenue towards the mechanochemical investigation of reactions comprising scarce, expensive, or toxic compounds. Our strategy is applied to model systems, including inorganic, metal-organic, and organic mechanosyntheses, resolves previously misinterpreted mechanisms in mechanochemical syntheses, and promises broad, new directions for mechanochemical research.

Metal-organic frameworks (MOFs) are microporous materials with huge potential as host structures for chemical processes, including retention, catalytic reaction, or separation of guest molecules. Structural collapse at high-pressure, and unusual behaviours at elevated temperatures, such as melting and transitions to liquid states, have recently been observed in the family. Here, we show that the effect of the application of simultaneous high-pressure and -temperature on a MOF can be understood in terms of silicate analogues, with crystalline, amorphous and liquid states occurring across the pressure - temperature phase diagram. The response of ZIF-62, the MOF on which we focus, to simultaneous pressure and temperature reveals a complex behaviour with distinct high- and low- density amorphous phases occurring over different regions of the pressure-temperature space. In-situ powder X-ray diffraction, Raman spectroscopy and optical microscopy reveal that the stability of the liquid MOF-state expands significantly towards lower temperatures at intermediate, industrially achievable pressures. Our results imply a novel route to the synthesis of functional MOF glasses at low temperatures, avoiding decomposition upon heating at ambient pressure.

We report a powerful example of subtle dynamic equilibrium control under milling conditions using the base catalysed solid state disulfide exchange reaction between two homodimers (bis-2-nitrophenyldisulfide and bis-4-nitrophenyldisulfide) to produce the heterodimer (4-nitrophenyl-2nitrophenyl-disulfide). Under ball mill neat grinding conditions, the equilibrium is reproducibly represented by homodimers and Form A of the heterodimer in a molar ratio of 1 to 4. The heterodimer crystallizes in two different polymorphic forms, Form A and Form B, which can be interconverted by changing the milling conditions between neat grinding and liquid assisted grinding with a number of solvents. Because such milling equilibria are reversible and dynamic in nature, we interpret these end points as existing in local thermodynamic wells. Moreover, homodimer bis-2-nitrophenyldisulfide also shows two polymorphs, Form I and Form II, depending on the milling conditions, further complicating the picture. Because of the nanocrystalline nature of these solid forms, we suggest that surface effects are responsible for the switch in polymorph stabilities in the milling jar.

Present estimates of the biogeochemical cycles of calcium, strontium, and potassium in the ocean reveal large imbalances between known input and output fluxes. Using pore fluid, incubation, and solid sediment data from North Pacific multi‐corer cores we show that, contrary to the common paradigm, the top centimeters of abyssal sediments can be an active site of authigenic precipitation of clay minerals. In this region, clay authigenesis is the dominant sink for potassium and strontium and consumes nearly all calcium released from benthic dissolution of calcium carbonates. These observations support the idea that clay authigenesis occurring over broad regions of the world ocean may be a major buffer for ocean chemistry on the time scale of the ocean overturning circulation, and key to the long‐term stability of Earth's climate.

The thesis developed in this chapter is that reactions taking place between molecular materials (intersolid) or within a molecular material (intrasolid) can be used to produce new crystalline materials in solvent‐free conditions and often with quantitative yields. The most common approach to intersolid and, to lesser extent, intrasolid processes is based on the mechanical cogrinding of the solid reactants, which implies comminution of the reactants. The implicit consequence of this is the lack of crystals of the product suitable for single‐crystal X‐ray diffraction. The mechanical process yields a polycrystalline or amorphous product, with structure and composition that often differ from that obtained from solution crystallization.