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High-pressure diffraction studies of molecular organic solids. A personal view

“…This holds for the polymorphs of paracetamol (Shakhtshneider et al, 1999;Boldyreva, Shakhtshneider et al, 2000;Boldyreva, Shakhtshneider, Ahsbahs, Sowa & Uchtmann, 2002), pentaerythrytol (Katrusiak, 1995), 1,3-cyclohexanedione (Katrusiak, 1990b), 2-methyl-1,3-cyclopentanedione (Katrusiak, 1990b(Katrusiak, , 1991b, sodium oxalate ( Orientation of the principal axes of the strain ellipsoid under pressure in -glycine with respect to the chains of the zwitterions in a layer; 1P -minimum, 3P -maximum compression, axis 2P is normal to the projection plane (based on data from Boldyreva et al, 2003). 2006).…”

“…For example, the compressibility of the OHÁ Á ÁO hydrogen bonds linking molecules into chains or layers in the structures of 1,3-cyclohexanedione, 2-methyl-1,3-cyclopentanedione and squaric acid is similar, whereas that of the OHÁ Á ÁO bonds linking the molecules of dimedone into helices is much higher (Katrusiak, 1990a(Katrusiak, ,b, 1991a. At the same time, the values of the compression of the NHÁ Á ÁO and OHÁ Á ÁO hydrogen bonds measured for chemically and structurally different compounds were close (Katrusiak, 1991a,b,c;Boldyreva et al, 1998;Boldyreva, Shakhtshneider et al, 2000;Boldyreva, 2003aBoldyreva, ,b, 2004aBoldyreva, Drebushchak, Shakhtshneider et al, 2004).…”

“…At the same time, they can find important applications in molecular electronics and in the pharmaceutical industry (Boldyreva & Boldyrev, 1999;Shakhtshneider et al, 1999;Hemley & Dera, 2000;Boldyreva, Shakhtshneider et al, 2000;Katrusiak, 2001;Boldyreva, 2003a,b;Fabbiani et al, 2003Fabbiani et al, , 2004Boldyreva, Drebushchak, Paukov et al, 2004;Boldyreva, Drebushchak, Shakhtshneider, Ahsbahs, Uchtmann et al, 2004;Fabbiani, Allan, Marshall et al, 2005Fabbiani et al, 2006Fabbiani et al, , 2007Boldyreva, 2006Boldyreva, , 2007a.…”

“…Linear strain in the crystal structure does not always correlate with the changes in the interatomic distances in the hydrogen bonds in the same directions due to the conformational changes and rotation of molecules (Boldyreva, 1994(Boldyreva, , 2001(Boldyreva, , 2003a(Boldyreva, ,b, 2004a(Boldyreva, ,b,c, 2006Boldyreva et al, 1997aBoldyreva et al, ,b, 1998Boldyreva, Shakhtshneider et al, 2000;Katrusiak, 1996Katrusiak, , 2001Katrusiak, , 2003Katrusiak, , 2004a. Hydrogen bonds can be compressed but the structure expands and, vice versa, the structure can be compressed despite the expansion of the intermolecular hydrogen bonds.…”

“…For example, in the monoclinic polymorph of paracetamol, all the intermolecular hydrogen bonds shorten with increasing pressure. Nevertheless, the structure expands in several crystallographic directions due to the flattening of the individual molecules and of the pleated hydrogen-bonded layers (Boldyreva, Shakhtshneider et al, 2000). Actually, the flattening of molecules and the shortening of the intermolecular hydrogen bonds are interrelated since the conformation of a paracetamol molecule is very sensitive to the charge distribution at the -OH, -C =O, -NH groups (Binev et al, 1998;Behzadi et al, 2007).…”