3,3,3-Trifluoro-2-hydroxy-2-(trifluoromethyl)propionic acid

In the title perfluorinated hydroxyisobutyric acid derivative, C4H2F6O3, the molecule shows approximately C s symmetry. The carboxy group is nearly coplanar with the C—OH moiety and the O=C—C—O(H) torsion angle is 5.5 (2)°. An intramolecular O—H⋯O hydrogen bond occurs. In the crystal, O—H⋯O hydrogen bonds connect the molecules into supramolecular chains along the a-axis direction.

In the title perfluorinated hydroxyisobutyric acid derivative, C 4 H 2 F 6 O 3 , the molecule shows approximately C s symmetry. The carboxy group is nearly coplanar with the C-OH moiety and the O C-C-O(H) torsion angle is 5.5 (2) . An intramolecular O-HÁ Á ÁO hydrogen bond occurs. In the crystal, O-HÁ Á ÁO hydrogen bonds connect the molecules into supramolecular chains along the a-axis direction.

3,3,3-Trifluoro-2-hydroxy-2-(trifluoromethyl)propionic acid Thomas Gerber and Richard Betz Comment
Chelate ligands have found widespread use in coordination chemistry due to the increased stability of coordination compounds they can form in comparison to monodentate ligands (Gade, 1998). Hydroxycarboxylic acids are particularily interesting in this aspect as they offer two hydroxyl groups of markedly different acidity as potential bonding partners.
Upon varying the substitution pattern on the hydrocarbon backbone, the acidity of the respective hydroxyl groups can be finetuned over a wide range and they may, thus, serve as probes for establishing the rules in which pK a range coordination to various central atoms can be observed. To allow for comparisons of metrical parameters of the carboxylic-acid-derived ligand in envisioned coordination compounds, the crystal and molecular structure of the free ligand was determined. The crystal structure of a related compound, 2-hydroxy-2-(trifluoromethyl)proprionic acid, is apparent in the literature (Soloshonok et al., 2007).
The carboxyl group is nearly in plane with the C-OH moiety. The respective O═C-C-O(H) torsion angle was found to be only 5.5 (2)°. This common plane also acts as internal mirror plane for the compound which shows approximately C s symmetry ( Fig. 1).
In the crystal, intermolecular hydrogen bonds can be observed. These are established between the carboxylic acid group as donor and the hydroxyl group as acceptor. The latter group itself, at the same time, acts as donor towards the doublebonded oxygen atom of the carboxyl group. The small dihedral angle among the O═C-C-O(H) moiety may be indicative of an intramolecular hydrogen bond as well, denoting the alcoholic hydroxyl group to give rise to a bifurcated hydrogen bond. Metrical parameters as well as information about the symmetry of these hydrogen bonds is summarized in Table 1.
In terms of graph-set analysis (Etter et al., 1990;Bernstein et al., 1995), the descriptor for the hydrogen bonds is S(5)C 1 1 (5)C 1 1 (5) on the unary level (Fig. 2). The packing of the title compound in the crystal structure is shown in Fig. 3.

Experimental
The compound was obtained from Alfa Aesar. Crystals suitable for the diffraction study were taken directly from the provided product.

Refinement
The H atoms of the hydroxyl groups were allowed to rotate with a fixed angle around the C-O bond to best fit the experimental electron density (HFIX 147 in the SHELX program suite (Sheldrick, 2008), with O-H = 0.84 Å, and with U(H) = 1.5U eq (O).