Pressure-induced polymorphism in phenol

Abstract

The high-pressure crystal structure of phenol (C(6)H(5)OH), including the positions of the H atoms, has been determined using a combination of single-crystal X-ray diffraction techniques and ab initio density-functional calculations. It is found that at a pressure of 0.16 GPa, which is just sufficient to cause crystallization of a sample held at a temperature just above its ambient-pressure melting point (313 K), a previously unobserved monoclinic structure with P2(1) symmetry is formed. The structure is characterized by the formation of hydrogen-bonded molecular chains, and the molecules within each chain adopt a coplanar arrangement so that they are ordered in an alternating 1-1-1 sequence. Although the crystal structure of the ambient-pressure P112(1) phase is also characterized by the formation of molecular chains, the molecules adopt an approximate threefold arrangement. A series of ab initio calculations indicates that the rearrangement of the molecules from helical to coplanar results in an energy difference of only 0.162 eV molecule(-1) (15.6 kJ mole(-1)) at 0.16 GPa. The calculations also indicate that there is a slight increase in the dipole moment of the molecules, but, as the high-pressure phase has longer hydrogen-bond distances, it is found that, on average, the hydrogen bonds in the ambient-pressure phase are stronger.

High-pressure crystallography

“…On the other hand, these huge pressures are comparable to the intermolecular interactions in crystal structures. Molecular crystals are formed by a very large group of organic compounds and it has already been recognized that pressure is an efficient method of generating new polymorphs (Boldyreva, 1990(Boldyreva, , 2004Allan et al, 1998;Allan & Clark, 1999;Allan et al, 2002;Boldyreva, Shakhtshneider, Ahsbahs, Sowa & Uchtmann, 2002;Boldyreva et al, 2003;Fabbiani et al, 2005;Podsiadło et al, 2005Podsiadło et al, , 2006Gajda et al, 2006;Gajda & Katrusiak, 2007;Bujak et al, 2007) and binary systems characteristic for high-pressure conditions only (Loubeyre et al, 1993(Loubeyre et al, , 1994Loubeyre, 1996;Kuhs, 2004). The higher the pressure, the further-reaching are the structural modifications.…”

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

“…Later, many examples were published in the papers by several groups (Fourme, 1968;Weir et al, 1969;Fourme et al, 1971;Allan et al, 1998;Allan & Clark, 1999a,b;Allan et al, 1999Allan et al, , 2001Allan et al, , 2002aKatrusiak et al, , 2007Podsiadło et al, 2005Podsiadło et al, , 2006Lozano-Casal et al, 2005;Gajda et al, 2005Gajda et al, , 2006Oswald, Allan, Day et al, 2005;Budzianowski et al, 2005;Budzianowski & Katrusiak, 2006a,b;Budzianowski et al, 2006;McGregor et al, 2006;Bujak et al, 2007;Dziubek et al, 2007;. Sometimes, the same polymorph is formed as a result of crystallization on cooling and with increasing pressure; examples are 1,2-dichloromethane (Podsiadło et al, 2005), and carbon disulfide .…”

“…One of the examples is water -ambient-pressure and high-pressure ices differ significantly in their structures and properties (Petrenko & Whitworth, 1999). Acetone (Allan & Clark, 1999b), acetic acid (Allan et al, 1999), alcohols (Allan et al, 1998(Allan et al, , 1999(Allan et al, , 2001, benzene (Fourme, 1968;Piermarini et al, 1969;Weir et al, 1969;Fourme et al, 1971;Budzianowski & Katrusiak, 2006a), chlorotrimethylsilane (Gajda et al, 2006), 1,2-dichloromethane (Podsiadło et al, 2005), sulfuric acid (Allan et al, 2002b), phenol (Allan et al, 2002a), 2-chlorophenol and 4-fluorophenol (Oswald, Allan, Day et al, 2005; are further examples of compounds, liquid at ambient conditions, which also give different polymorphs on cooling and with increasing pressure.…”

Prediction of the crystal structures of axitinib, a polymorphic pharmaceutical molecule

“…Thus, there are emerging attempts (Day et al, 2003;Karamertzanis et al, 2008;van Eijck, 2001;Vasileiadis, 2013) to take some account of entropic contributions. A further approximation is usually made to neglect the pV term, as this is very small (of the order of J mol À 1 ) at low pressures, only becoming practically important at pressures of the order of GPa (Admiraal et al, 1982;Allan et al, 2002;Paliwoda et al, 2012).…”