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 in situ spectroscopic and kinetic data are supported by ex situ X-ray diffraction and solid-state nuclear magnetic resonance spectroscopy measurements. The application of first principles (ab initio) calculations enabled the elucidation of how changes in crystalline environment, that result from mechanochemical reactions, affect vibrational and electronic excited states of molecules. The herein explored interpretation of both real-time and ex situ spectroscopic data through ab initio calculations provides an entry into developing a detailed mechanistic understanding of mechanochemical milling processes and highlights the challenges of using real-time spectroscopy

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. The results of this study credibly extend the scope of crystal engineering and cocrystallization from small molecules to polymers

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. The results of this study credibly extend the scope of crystal engineering and cocrystallization from small molecules to polymers

Rational Synthesis of Mixed-Metal Microporous Metal–Organic Frameworks with Controlled Composition Using Mechanochemistry

Mechanochemistry enables targeted, rapid synthesis of bimetallic metal−organic frameworks (MOFs) with a controlled 1:1 stoichiometric composition of metal nodes. In particular, ball milling enabled the use of specifically synthesized solid coordination complexes of Zn(II), Mg(II), Ni(II), and Co(II) for the assembly of a range of microporous mixed-metal MOF-74 materials composed of pairs of d-block or main group metals in a predetermined 1:1 stoichiometric ratio, including ZnMg-, ZnCo-, ZnCu-, MgZn-, MgCo-, NiZn-, NiMg-, NiCo-, CoZn-, CoMg-, CoCu-, and MgCa-MOF-74. By using specifically prepared precursors in the ynthesis of diverse mixed-metal MOF-74 targets, this rational synthesis represents the first entry of mechanochemistry into the target-oriented synthesis of mixed- metal MOFs

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

Synthesis, Structures and Properties of Cobalt Thiocyanate Coordination Compounds with 4-(hydroxymethyl)pyridine as Co-ligand

Reaction of Co(NCS)2 with 4-(hydroxymethyl)pyridine (hmpy) leads to the formation of six new coordination compounds with the composition [Co(NCS)2(hmpy))4] (1), [Co(NCS)2(hmpy)4] × H2O (1-H2O), [Co(NCS)2(hmpy)2(EtOH)2] (2), [Co(NCS)2(hmpy)2(H2O)2] (3), [Co(NCS)2(hmpy)2]n∙4 H2O (4) and [Co(NCS)2(hmpy)2]n (5). They were characterized by single crystal and powder X-ray diffraction experiments, thermal and elemental analysis, IR and magnetic measurements. Compound 1 and 1-H2O form discrete complexes, in which the Co(II) cations are octahedrally coordinated by two terminal thiocyanato anions and four 4-(hydroxymethyl)pyridine ligands. Discrete complexes were also observed for compounds 2 and 3 where two of the hmpy ligands were substituted by solvent, either water (3) or ethanol (2). In contrast, in compounds 4 and 5, the Co(II) cations are linked into chains by bridging 4-(hydroxymethyl)pyridine ligands. The phase purity was checked with X-ray powder diffraction. Thermogravimetric measurements showed that compound 3 transforms into 5 upon heating, whereas the back transformation occurs upon resolvation. Magnetic measurements did not show any magnetic exchange via the hmpy ligand for compound 5

Profound Effect of the Milling Assembly on Polymorphism in Mechanochemical Cocrystallization

Mechanochemistry provides a highly efficient, but still poorly understood route to synthesize and screen for polymorphs of organic solids. We present a hitherto unexplored approach to control the mechanism and outcome of mechanochemical cocrystallization through changes to the milling assembly, i.e. milling jar and balls. Whereas polymorph control of mechanochemical cocrystallization is typically discussed in terms of liquid additives, real-time synchrotron X-ray diffraction studies reveal a direct impact of the choice of milling media on the rate of formation and interconversion of cocrystal polymorphs. This effect enabled the discovery of a new polymorph of a cocrystal of nicotinamide and adipic acid, whose formation and conversion to the previously known, enantiotropically-related form, was readily controlled by milling in jars made of different materials