Mechanochemical stability of hydrogen titanate nanostructures

Structural stability of nanostructured titanates was investigated for further processing and possible applications. With the aim to investigate their mechanochemical stability we applied highenergy ball milling and studied induced phase transitions. Hydrogen titanates having two different morfologies, microcrystals and nanotubes, were taken into consideration. During mechanochemical treatment of both morphologies, we observed the phase transition from hydrogen titanate to TiO2 anatase and then to TiO2 rutile. Anatase to rutile phase transition occurred without appearance of intermediate high pressure TiO2 II typically observed in the case of mechanochemical treatment of TiO2. In the case of microcrystals, phase transition from hydrogen titanate to anatase starts after longer milling time than in the case of nanotubes, which is explained by larger particles sizes of crystalline powder. On the contrary, further phase transition from anatase to rutile was occurred faster in crystalline powder than in the case of nanotubes. The sequence of phase transitions was studied by Raman spectroscopy and X-ray powder diffraction, while morphology and crystal structure at nanoscale were analyzed by high resolution electron microscopy

Time-dependent density-functional theory for modeling solid-state fluorescence emission of organic multicomponent crystals

We describe the approach for modeling solid-state fluorescence spectra of organic crystalline materials, using the recent implementation of time-dependent density-functional theory within the plane-wave/pseudopotential code CASTEP. The method accuracy is evaluated on a series of organic cocrystals displaying a range of emission wavelengths. In all cases the calculated spectra are in good to excellent agreement with experiment. The ability to precisely model the emission spectra offers novel insight into the role of intermolecular interactions and crystal packing on solid-state luminescence of organic chromophores, allowing the possibility of <i>in silico</i> design of organic luminescent materials

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

Computational evaluation of metal pentazolate frameworks::Inorganic analogues of azolate metal-organic frameworks

We report a periodic density-functional theory evaluation of putative frameworks, including a topologically novel arhangelskite (arh) structure, based on the pentazolate ion, the ultimate all-nitrogen, inorganic member of the azolate series of aromatic 5-membered ring anions.</p