s13.m37.o6 In situ pressure crystallization: an alternative to crystallization by cooling

In situ crystallization of liquids is usually connotated with the crystallization by lowering temperature, which started to be routinely applied in the 1950's [e.g. 1-4], and was perfected in the 1980's [5,6]. In situ temperature crystallization is routinely applied in neutron diffraction. In fact the low-temperature diffraction studies are regarded as the most accurate structural data. At the same time the crystallization of liquids can be achieved by elevating pressure. Therefore soon after the inception of the high-pressure diamond cell (DAC) the pressure technique was applied for in situ crystallization [7-9], and has been used for a number of studies [e.g. see 10]. However the precision of the high-pressure data is still inferior than the low-temperature results, even though in a small number of studies a comparable accuracy of the pressure results was demonstrated for laboratory [11] and synchrotron [12] studies on organic compounds. Most recently we have implemented a series of data correcting programs [13] and methods [14] which facilitate in situ pressure crystallization and considerably improve the accuracy of single-crystal high-pressure results measured with a DAC and a CCD diffractometer. The methods will be outlined, and the quality of the measured data exemplified. The primary aim of our pressure structures are intermolecular interactions in crystals and conformational transformations of molecules.