Michael Ferguson

Discovery of a polymorph of tris( p‐ tolyl)antimony(III) reveals solid‐state supramolecular dimers connected through short, attractive Sb∙∙∙Sb contacts that, based on theoretical calculations and a systematic screen of the Cambridge Structural Database (CSD), could be an overlooked hallmark of the solid‐state and supramolecular chemistry of trivalent organoantimony(III) compounds. While the previously reported crystal structure of tris( p‐ tolyl)antimony(III) is known to exhibit phenyl embrace motifs, resembling the arsenic or phosphorus analogs, the new polymorph exhibits supramolecular dimers characterized by direct Sb∙∙∙Sb contacts shorter than the sum of the van der Waals radii, and stabilized by a significant dimer dissociation energy of ca. −26 kJ mol ⁻¹ established by periodic density‐functional calculations. Theoretical analysis indicates that the contacts are attractive and dispersion‐dominated, with an overview of the CSD showing that such direct Sb···Sb contacts are not unique to this polymorphic form of tris( p‐ tolyl)antimony(III) but appear to be a more general feature of trivalent organoantimony in the solid state. Specifically, the CSD shows that dimers based on short Sb···Sb contacts are found across a number of organoantimony structures, including some of the simplest representatives of the series, such as triphenyl‐ and trimethylantimony, for which the dimer interaction energy is herein calculated to be ca. −13 kJ mol ⁻¹ .

Discovery of a polymorph of tris( p‐ tolyl)antimony(III) reveals solid‐state supramolecular dimers connected through short, attractive Sb∙∙∙Sb contacts that, based on theoretical calculations and a systematic screen of the Cambridge Structural Database (CSD), could be an overlooked hallmark of the solid‐state and supramolecular chemistry of trivalent organoantimony(III) compounds. While the previously reported crystal structure of tris( p‐ tolyl)antimony(III) is known to exhibit phenyl embrace motifs, resembling the arsenic or phosphorus analogs, the new polymorph exhibits supramolecular dimers characterized by direct Sb∙∙∙Sb contacts shorter than the sum of the van der Waals radii, and stabilized by a significant dimer dissociation energy of ca. −26 kJ mol ⁻¹ established by periodic density‐functional calculations. Theoretical analysis indicates that the contacts are attractive and dispersion‐dominated, with an overview of the CSD showing that such direct Sb···Sb contacts are not unique to this polymorphic form of tris( p‐ tolyl)antimony(III) but appear to be a more general feature of trivalent organoantimony in the solid state. Specifically, the CSD shows that dimers based on short Sb···Sb contacts are found across a number of organoantimony structures, including some of the simplest representatives of the series, such as triphenyl‐ and trimethylantimony, for which the dimer interaction energy is herein calculated to be ca. −13 kJ mol ⁻¹ .

We demonstrate a systematic application of the mechanochemical liquid-assisted grinding (LAG) methodology to screen for forms of zinc imidazolate (ZnIm₂), of fundamental importance as the simplest member of the zeolitic imidazolate framework materials family. The exploration of 45 different liquid additives, selected based on their molecular structure and physicochemical properties has resulted in eight different ZnIm₂ topological forms, appearing in 13 crystallographically distinct solid forms (including two previously unknown forms of the crb (BCT) topology), amorphous phases, and the interrupted moc-Zn₄Im₈HIm. All prepared topological forms were also explored computationally, using dispersion-corrected periodic density functional theory (DFT) calculations, enabling the rationalization of screening outcomes, and setting the stage for future prediction of additive-directed metal-organic framework (MOF) synthesis. This first systematic exploration of LAG in screening for three-dimensional MOFs demonstrates the potential of the liquid additive to not only accelerate materials synthesis, but also to direct it toward topologically different MOFs. The discovery of novel forms of a material that already exhibits at least 21 crystallographically and functionally different forms provides a strong testimony on the power of mechanochemistry in metal-organic materials discovery.

We describe a computational modeling strategy to investigate the dynamics and mobility of molecules in systems that compositionally correspond to the liquid-assisted environments, which are of importance to increasingly popular mechanochemical and other solvent-limited systems in which the amount of a liquid phase is tens or hundreds of times smaller compared to conventional solution environments. This work investigates how the presence of minute quantities of intimately mixed-in small-molecule solvents can influence the rigidity and mobility of an initially crystalline molecular solid, offering a starting point towards the understanding and modelling of liquid-assisted reactivity of relevance in mechanochemistry, as well as to a wide range of aging transformations relevant to, for example, the environmental stability of molecular solids such as pharmaceuticals. In effect, this study allowed us to evaluate changes to the molecular and structural dynamics with increasing amounts of a liquid additive, providing a nanoscopic view of the liquid-assisted environment, based on the number and choice of the additive and their nature, contextualized in the macroscopic and experimentally relevant η parameter. This represents, to our knowledge, the first attempt at an in silico modelling study to understand the fundamental aspects of the liquid-assisted environments found in a wide range of mechanochemical and mechanically-activated reactions. The herein presented theoretical modelling approach should be seen as a step towards detailed, quantitative studies of how the liquid-assisted environments might compare to bulk-solution environments characteristic of traditional solvent-based chemistry.

We demonstrate a systematic application of the mechanochemical liquid-assisted grinding (LAG) methodology to screen for forms of zinc imidazolate (ZnIm2), of fundamental importance as the simplest member of the zeolitic imidazolate framework materials family. The exploration of 45 different liquid additives, selected based on their molecular structure and physicochemical properties has resulted in seven different ZnIm2 topologies, appearing in 12 structurally distinct solid forms (including two previously unknown forms of the crb (BCT) topology), amorphous phases, and the interrupted moc topology material. All prepared topologies were also explored computationally, using dispersion-corrected periodic density functional theory (DFT) calculations, enabling the rationalization of screening outcomes, and setting the stage for future prediction of additive-directed MOF synthesis. This first systematic exploration of LAG in screening for three-dimensional metal-organic frameworks demonstrates the potential of the liquid additive to not only accelerate materials synthesis, but also to direct it towards topologically different frameworks. The ability to discover novel forms in a material that already exhibits at least 21 crystalographically and functionally different forms provides a strong testimony on the power of mechanochemistry in metal-organic materials discovery.

The herein revisited 1967 attempt of structural analysis of the solid-state complex of caffeine and pyrogallol was a pioneering investigation of what today would be seen as a prototypical pharmaceutical cocrystal model system.

Solid-state reaction of the active pharmaceutical ingredient theophylline with citric acid is a well-established example of a mechanochemical reaction leading to a model pharmaceutical cocrystal. Here, classical force field molecular dynamics were employed to investigate molecular mixing and structural distortion that take place upon mechanically driven indentation of a citric acid nanoparticle upon a slab of crystalline theophylline. Through non-equilibrium molecular dynamics simulations, a 6 nm diameter nanoparticle of citric acid was introduced onto an open (001) surface of a theophylline crystal, varying both the angle of incidence of the nanoparticle between 15 ° and 90 ° and the indentation speed between 1 m s⁻¹ and 16 m s⁻¹. This theoretical study enabled the evaluation of how these two parameters promote molecular mixing and overall structural deformation upon mechanical contract of theophylline and citric acid, both of which are important parameters underlying mechanochemical cocrystallisation. The results show that the angle of incidence plays a key role in the molecular transfer ability between the two species and in the structural disruption of the initially spherical nanoparticle. Changing the indentation speed, however, did not lead to a discernible trend in molecular mixing, highlighting the importance of the incident angle in mechanochemical events.

Solid-state reaction of the active pharmaceutical ingredient theophylline with citric acid is a well-established example of a mechanochemical reaction leading to a model pharmaceutical cocrystal. Here, classical force field molecular dynamics was employed to investigate molecular mixing and structural distortion that take place upon mechanically driven indentation of a citric acid nanoparticle upon a slab of crystalline theophylline. Through non-equilibrium molecular dynamics simulations, a 6 nm diameter nanoparticle of citric acid was introduced onto an open (001) surface of a theophylline crystal, varying both the angle of incidence of the nanoparticle between 15◦ and 90◦ and the indentation speed between 1ms−1 and 16ms−1. This theoretical study enabled the evaluation of how these two parameters promote molecular mixing and overall structural deformation upon mechanical contract of theophylline and citric acid, both of which are important parameters underlying mechanochemical cocrystallisation. The results show that the angle of incidence plays a key role in the molecular transfer ability between the two species and in the structural disruption of the initially spherical nanoparticle. Changing the indentation speed, however, did not lead to a discernible trend in molecular mixing, highlighting the importance of the incident angle in mechanochemical events.

As we strive to perform chemical transformations in a more sustainable fashion, enabling solid-state reactions through mechanochemistry has emerged as a highly successful approach. Due to the wide-ranging applications of gold nanoparticles (AuNPs), mechanochemical strategies have already been employed for their synthesis. However, the underlying processes surrounding gold salt reduction, nucleation and growth of AuNPs in the solid state are yet to be understood. Here, we present a mechanically activated aging synthesis of AuNPs, through a solid-state Turkevich reaction. Solid reactants are only briefly exposed to input of mechanical energy before being aged statically over a period of six weeks at different temperatures. This system offers an excellent opportunity for an in situ analysis of both reduction and nanoparticle formation processes. During the aging period, the reaction was monitored using a combination of X-ray photoelectron spectroscopy, diffuse reflectance spectroscopy, powder X-ray diffraction and transmission electron microscopy, to gain meaningful insights into the mechanisms of solid-state formation of gold nanoparticles. The acquired data allowed for the establishment of the first kinetic model for solid-state nanoparticle formation.