2,2,3,3,4,4,5,5-Octafluorohexane-1,6-diol

The title compound exhibits gauche–trans–trans O—C—C—O conformations. The conformational configuration is driven by the formation of an extended hydrogen-bonding network among the terminal alcohol groups of each molecule.

In the crystal of the title compound, C 6 H 6 F 8 O 4 , O-HÁ Á ÁO hydrogen bonds involving the hydroxy groups connect the molecules, forming a two-dimensional network parallel to (100). These hydrogen-bonding interactions appear to drive the O-C-C-O torsion angles into a gauche-trans-trans series of conformations along the backbone of the molecule.

Structure description
Ionic liquids have attracted considerable interest as solvents for a variety of applications. 'Solvate' ionic liquids (SILs) are a new class of ionic liquids that consist of equimolar mixtures of inorganic salts and molecular solvents capable of chelating the cations of the salt (Ueno et al., 2012Mandai et al., 2014Mandai et al., , 2015. Most research on SILs focus on methyl-capped ethylene oxide molecular solvents, which are collectively known as 'glymes'. Structural variation of the chelating compound will undoubtedly influence cation-solvent interactions and provide alternative means for tuning SIL properties (Saito et al., 2016). Our lab has pursued this line of research by examining partially fluorinated molecular solvents for SIL applications. During our experiments, we isolated and determined the structure of the title compound, a partially fluorinated derivative of triethylene glycol. The molecular structure of the title compound is shown in Fig. 1. In the crystal, O-HÁ Á ÁO hydrogen bonds involving the terminal hydroxyl groups (see Table 1) connect the molecules, forming a two-dimensional network parallel to (100) (Fig. 2). In addition, a weak intermolecular C-HÁ Á ÁF hydrogen bond is observed within this network. These hydrogen-bonding interactions appear to drive the O-C-C-O torsion angles into a gauche-trans-trans series of conformations along the backbone of the molecule: O1-C1-C2-O2 = 66.3 (2), O2-C3-C4-O2 = À168.91 (15), and O3-C5-C6-O4 = À177.92 (15) . By way of comparison, the O-C-C-O torsion angles data reports are gauche in monoglyme (Yoshihiro et al., 1996) and longer chain glymes (Johansson et al., 2010;Hyun et al., 2001;Tadokoro, 1964).

Refinement
Crystal data, data collection methods, and structural refinement details are provided in Table 2. The absolute structure of the title compound could not be established in the refinement reported here.

Funding information
Funding for this research was provided by: American Chemical Society Petroleum Research Fund (grant No. 57803-

Figure 1
The molecular structure of the title compound. Displacement ellipsoids are shown at 50% probability level.  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.65 e Å −3 Δρ min = −0.40 e Å −3 Absolute structure: Refined as an inversion twin Absolute structure parameter: 0.5 (6) Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. Refinement. Refined as a 2-component inversion twin.