[1,1′-Bicyclohexane]-1,1′-diol

The title compound is a symmetric diol derived from the pinacol coupling of cyclohexanone. The asymmetric unit contains three complete molecules. Cooperative hydrogen bonding connects the individual molecules into infinite chains propagating along the crystallographic a-axis direction.

The title compound, C 12 H 22 O 2 , is a symmetric diol derived from the pinacol coupling of cyclohexanone.The asymmetric unit contains three complete molecules.The cyclohexane moieties adopt chair conformations.Cooperative hydrogen bonding connects the individual molecules to infinite chains propagating along the crystallographic a-axis direction.

Structure description
Chelating 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).Diols are particularly interesting in this aspect as they offer two hydroxyl groups that -depending on the experimental conditions -can either act as fully neutral, fully anionic or mixed neutral-anionic ligands.Upon varying the substitution pattern on the hydrocarbon backbone, the acidity of the respective hydroxyl groups can be fine-tuned 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.Furthermore, the steric pretence of potential substituents may give rise to unique coordination and bonding patterns.To allow for comparisons of metrical parameters of the title compound in envisioned coordination compounds, the crystal and molecular structure of the free ligand was determined.The crystal structures of the related pinacols derived from cyclopentanone (Hosten & Betz, 2021), cycloheptanone (Betz & Klu ¨fers, 2007) and cyclododecanone (Yang et al., 2016) are apparent in the literature.Structural data of symmetric pinacols derived from methyl-substituted (Bruss et al., 1987) and phenyl-substituted cyclohexanones (Nieger et al., 2004) have been reported.Furthermore, metrical information based on diffraction studies of other sterically demanding diols such as 1,2-di-tert-butyl-ethane-1,2-diol (Kerscher et al., 2009), 1,2-dicyclopentylethane-1,2-diol (Betz et al., 2007), as well as cis-1,2-dimethyl-cyclobutane-1,2-diol (Allscher et al., 2008) are available.The crystal and molecular structure of a coordination compound of osmium featuring the title compound as chelating ligand is apparent in the literature (Lehtonen et al., 1999).
The asymmetric unit of the title compound is shown in Fig. 1 and contains three complete molecules.Bond lengths and angles are normal and in good agreement with values reported for other symmetric pinacols.The hydrogen atoms of the hydroxyl groups are disordered over two orientations.A conformational analysis of the cyclohexane rings (Cremer & Pople, 1975) shows the latter to invariably adopt chair conformations (Boeyens, 1978)  In the crystal, classical hydrogen bonds of the O-H� � �O type are apparent that involve all hydroxyl groups as donors and acceptors (Table 1), forming cooperative cyclic patterns.In terms of graph-set analysis (Etter et al., 1990;Bernstein et al., 1995), the descriptor for these hydrogen bonds is data reports

Figure 1
The molecular structure of the title compound, with atom labels and anisotropic displacement ellipsoids (drawn at the 50% probability level).For clarity, only one of the two disordered hydrogen-atom positions is depicted.

Table 1
Hydrogen-bond geometry (A ˚, � ).DDDDDD on the unary level while an R 6 6 (12) descriptor is required on the hexanary level.The molecule featuring the anti-orientated hydroxyl groups acts as a linker between these various trimeric arrangements, thus giving rise to infinite chains of the hitherto hydrogen-bonded molecules along the crystallographic a-axis direction.A depiction of the pattern is shown in Fig. 2.

Synthesis and crystallization
The title compound was synthesized from cyclohexanone according to a published procedure (Criegee et al., 1952).Crystals suitable for the diffraction study were obtained upon slow evaporation of a solution of the compound in THF at room temperature.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2.The carbon-bound H atoms of the methylene groups were placed in calculated positions (C-H 0.99 A ˚) and were included in the refinement in the riding model approximation, with U iso (H) set to 1.2U eq (C).The H atoms of the hydroxyl groups were located in a DFM accounting for the equal disorder over two positions, with U iso (H) set to 1.5U eq (O).

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.
with each of the three molecules featuring one ring in a 1 C 4 and the second ring in a 4 C 1 conformation.In two of the three molecules, the hydroxyl groups adopt a somewhat staggered conformation with respective O-C-C-O torsion angles of 50.95 (11) and 55.14 (10) � , while in the third molecule the two alcoholic groups are arranged in an almost perfect anti conformation with the pertaining O-C-C-O angle measuring À 177.82 (9) � .

Figure 2
Figure 2 Intermolecular contacts, viewed approximately along [011].For clarity, only one of the two disordered hydrogen-atom positions is depicted.

Table 2
Experimental details.