title: Structures of the monofluoro- and monochlorophenols at low temperature and high pressure.
abstract: 2-Fluorophenol, 3-fluorophenol and 3-chlorophenol were recrystallized from frozen solids at 260, 263 and 283 K. All compounds were also crystallized by the application of high pressure (0.36, 0.12 and 0.10 GPa). While 3-fluorophenol and 3-chlorophenol yielded the same phases under both conditions, different polymorphs were obtained for 2-fluorophenol. 4-Chlorophenol was crystallized both from the melt and from benzene to yield two different ambient-pressure polymorphs; crystallization from the melt at 0.02 GPa yielded the same phase as from benzene at ambient pressure. 3-Fluorophenol is unusual in forming a hydrogen-bonded chain along a 2(1) screw axis. Such behaviour is usually only observed for small alcohols, but here it appears to be stabilized by intermolecular C-H...F hydrogen-bond formation. 3-Chlorophenol is a more typical large alcohol and emulates a fourfold screw axis with two independent molecules positioned about a 2(1) axis, although there are significant distortions from this ideal geometry. The two phases of 4-chlorophenol consist of chains or rings connected by C-Cl...H interactions. The low-temperature and high-pressure polymorphs of 2-fluorophenol consist of chains of molecules connected through OH...OH hydrogen bonds; while inter-chain C-H...F interactions are significant at high pressure, there are none in the low-temperature form.
authors.affiliation: School of Chemistry and The Centre for Science at Extreme Conditions, The University of Edinburgh, King's Buildings, West Mains Road, Edinburgh EH9 3JJ, Scotland.
authors.forename: Iain D H
authors.initials: ID
authors.lastname: Oswald
authors.forename: David R
authors.initials: DR
authors.lastname: Allan
authors.forename: W D Samuel
authors.initials: WD
authors.lastname: Motherwell
authors.forename: Simon
authors.initials: S
authors.lastname: Parsons
mesh_terms: D002733:Chlorophenols / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D010636:Phenols / Q000737:chemistry*; D011312:Pressure; D013696:Temperature; D014961:X-Ray Diffraction
chemical_list: D002733:Chlorophenols; D010636:Phenols; C487839:2-fluorophenol; C085046:3-fluorophenol; C030682:3-chlorophenol