Pressure-induced structural changes in some molecular and ionic-molecular crystals: experimental studies and computer simulations

Elena V. Boldyreva

Institute of Solid State Chemistry and Mechanochemistry, Siberian Branch of the Russian Academy of Sciences, Kutateladze, 18, Novosibirsk, 128, RUSSIA, and

Research and Education Center “Molecular Design and Ecologically Safe Technologies” Novosibirsk State University, Pirogova, 2, Novosibirsk, 90, RUSSIA

Pressure is one of the parameters characterizing the conditions, under which a solid and its transformations can be considered. However, until recently, variable-pressure studies were less common than the variable-temperature ones, mainly due to the experimental difficulties. Nowadays, the situation is being changed very quickly, and high-pressure diffraction, spectroscopy, microscopy studies become more and more common.

The effect of pressure on solids and their transformations can be considered in the following aspects:

- High pressure as a tool for the crystallization of new polymorphs (starting from the liquid state) ;

- High pressure as a tool for the synthesis of new chemical compounds;

- Polymorphic transformations induced by high pressure;

- Effect of high pressure on the chemical reactions induced by other means (temperature, light, etc.), in particular – kinetic effects;

- Anisotropy of pressure-induced structural strain within the range of stability of the same polymorph.

The high-pressure studies can provide valuable information on the structure-properties relationships, on the nature and the characteristics of intermolecular interactions, on the factors determining crystal structures (important for crystal engineering) and solid state reactivity.

The lecture will give a general introduction into some of these problems, with a special emphasis on the pressure-induced polymorphic transformations, the anisotropy of the pressure-induced strain in the same polymorph, and on the kinetic effects of pressure on solid-state reactions.

As examples, the effect of pressure on various molecular and ionic-molecular compounds with flexible / rigid structure-forming units and various types of hydrogen bonds will be considered. Among them, there are Co(III) nitro / nitrito-ammine complexes, sodium oxalate, benzoquinone, serine, the polymorphs of glycine, and of paracetamol. The results of the experimental study (single-crystal and powder X-ray diffraction, IR- and Raman spectroscopy, optical microscopy) will be discussed and compared with those from the computing simulations.