CommentThe title molecule has been used in the past as an antiseptic, a pesticide for wood, leather and glue preservation, and also as an antimildew treatment for textiles. However, production was discontinued in the 1980 s and the molecule is no longer used in the USA, mainly because its production process systematically affords small quantities of dioxins and dibenzofurans. This molecule is currently listed as "reasonably anticipated to be a human carcinogen" (US Department of Health and Human Services, 2005). The corresponding phenolate has been used as a ligand for transition and non-transition metal ions, e.g.Cu II (Gökaugaç et al., 1999), Mn III (Wesolek et al., 1994), or Mg II (Zechmann et al., 2000).The molecular structure ( Fig. 1) approximates a C 2v symmetry. However, the molecule is placed on a general position.The hydroxyl H atom lies in the plane of the aromatic ring and is oriented toward Cl6. The corresponding site oriented toward Cl2 is not available for hydroxyl H atom, as, due to crystal symmetry, it would give a short intermolecular H···H contact.Interestingly, two polymorphs of pentafluorophenol have been reported (Das et al., 2006). For the Z' = 1 polymorph, hydroxyl H atom is placed 0.36 Å above the aromatic ring. A second polymorph, with Z' = 3, shows a variety of hydroxyl conformations. Two molecules are almost planar, with H deviations of 0.10 and 0.04 Å, while the third one has O-H bond almost normal to the aromatic ring, with the H atom placed 0.66 Å out of the benzene mean plane. In the same way, the title compound could present a degree of free rotation about the C-O bond, allowing the stabilization of polymorphic phases.Regarding the crystal structure, no significant π···π interactions are observed. The closest approach between centroids of aromatic rings of symmetry-related molecules is 3.818 Å. ExperimentalA sample of the title compound was donated by the Chemistry Stores at Universidad Autónoma de Nuevo León (UANL), and used without previous recrystallization. RefinementAll H atoms were found in a difference map, but their positions regularized in order to get an idealized geometry for C-H and O-H groups. Constrained bond lengths: 0.82 (hydroxyl OH) and 0.93 Å (aromatic CH). Isotropic displacement parameters for H atoms were fixed to U iso (H1) = 1.5 U eq (O1); U iso (H3) = 1.2 U eq (C3); U iso (H5) = 1.2 U eq (C5). supplementary materials sup-2

Key indicators: single-crystal X-ray study; T = 299 K; mean (C-C) = 0.004 Å; disorder in main residue; R factor = 0.055; wR factor = 0.156; data-to-parameter ratio = 12.0.