4-(4-Hydroxyphenyl)-2,2,4-trimethyl-7,8-benzothiachroman, a fused-ring counterpart of thia-Dianin’s compound

In the title compound, both independent molecules possess a very similar proximal conformation, this referring to the juxtaposition of the 4-hydroxyphenyl substituent with respect to the syn-related methyl group.

The title compound, C 22 H 22 OS [systematic name: 4-(1,3,3-trimethyl-2,3-dihydro-1H-4-thiaphenanthren-1-yl)phenol], crystallizes unsolvated from nitromethane as colourless prisms (m.p. 425-427 K) in the polar monoclinic space group Ia with Z 0 = 2 (molecules A and B). Both independent molecules possess a very similar proximal conformation, this referring to the juxtaposition of the 4hydroxyphenyl substituent with respect to the syn-related methyl group. In the crystal, molecule A is linked to molecule B by an O-HÁ Á ÁO hydrogen bond. In turn, molecule B exhibits a weak O-HÁ Á Á interaction with the phenolic group of molecule A related by a-glide symmetry. Together, these lead to [100] chains.

Chemical context
As part of a detailed study of clathrate formation by systems related to Dianin's compound (Frampton et al., 2013(Frampton et al., , 2017aMacNicol, 1984), we have investigated structural modifications of thia-Dianin's compound 2, the direct thiachroman counterpart of Dianin's compound itself, 3. This led to interesting and diverse outcomes: (i) oxidation of 2 gave the colourless and beautifully crystalline sulfone 4, which crystallises in the polar space group Cc with Z 0 = 1; (ii) crystals of 4 exhibit a significant second-harmonic generation (SHG) effect (Frampton et al., 1992); (iii) introduction of a methyl group at position carbon-7 led to spontaneous resolution with a structure in P2 1 2 1 2 1 , Z 0 = 1; and (iv) introduction of a methyl group at either the 6-or 8-position yielded new clathrate systems isomorphous with 2 and 3, space group R3 (Hardy et al., 1979). The latter clathrate networks are comprised of columns formed from infinite stacking of hexameric hydrogen-bonded [OH] 6 units along the c-axial direction, with clathrate formation being dependent upon efficient packing with adjacent threefold screw-related columns. Compound 1 was prepared to establish the effect on the resulting crystal packing of substantially extending the molecular skeleton of 2; the introduction of the bulky benzo group was expected to cause serious disruption to the intercolumn packing.

Structural commentary
The crystal structure of 1 is monoclinic, space group Ia, with two independent molecules in the asymmetric unit (Z 0 = 2). For clarity, each independent molecule is labelled with the suffix A or B, respectively. Figs. 1 and 2 show displacement ellipsoid plots for the two independent molecules. Both ISSN 2056-9890 independent molecules possess a very similar proximal conformation, this referring to the juxtaposition of the 4-hydroxyphenyl substituent with respect to the syn-related methyl group. The C2-C3-C4-C11 torsion angles for molecules A and B are 79.5 (4) and 81.4 (4) , respectively; the corresponding torsion angle for racemic Dianin's compound has magnitude 80.67 (Lee et al., 2014). The expected torsion angle value for a distal conformation is $160 . The torsion angle S1-C2-C3-C4, defining the heterocyclic ring chirality, has values of 62.8 (3) and 63.3 (3) for A and B, respectively. Fig. 3 shows an overlay (Macrae et al., 2008) of molecules A and B shown in blue and brown, respectively, with an r.m.s. displacement of 0.0789 Å . In addition to showing the proximal conformation of both molecules, it can be seen that the two molecules differ only in the directional orientation of the phenolic H atom. The dihedral angles between the naphthalene C5-C10/C20-C23 ring system and the C11-C16 phenol ring are 74.25 (9) and 70.57 (9) for molecules A and B, respectively. It is clear that the addition of the fused benzo ring to the thia-Dianin framework across positions C7 and C8 has caused significant disruption to the intercolumn packing to prevent formation of the conventional R3 host lattice.

Supramolecular features
A view of the crystal packing down the c axis is shown in Fig. 4. In the crystal the two independent molecules in the asymmetric unit, A and B, are linked by an O-HÁ Á ÁO hydrogen bond (Table 1). Molecule B exhibits a weak O-HÁ Á Á interaction, shortest length H1BÁ Á ÁC16A = 2.54 (6) Å (this being some 0.35 Å less than the Pauling sum of the van der Waals radii of 2.88 Å ), with the phenolic group of molecule A related by a-glide symmetry. These two distinct hydrogen-bond interactions can be clearly detected in the IR spectrum of 1 with strong OH vibrational frequencies of 3409 and 3527 cm À1 , respectively. The result is the formation of an infinite chain of molecules alternately linked by O-HÁ Á ÁO View of molecule B of the asymmetric unit with the atom labelling. Displacement ellipsoids are drawn at the 50% probability level.

Figure 1
View of molecule A of the asymmetric unit with the atom labelling. Displacement ellipsoids are drawn at the 50% probability level. Table 1 Hydrogen-bond geometry (Å , ).

Database survey
The structure and absolute stereochemistry determination of the resolved S-enantiomer of thia-Dianin's compound was used in the formation of the quasi-racemates above (BIBNEH; Frampton et al., 2013).

Synthesis and crystallization
Compound 1 was produced, as described in the literature, by the action of gaseous hydrogen chloride on a mixture of phenol and 4-methyl-4-(1-naphthylsulfanyl)pentan-2-one (Hardy et al., 1979). Unsolvated colourless prisms suitable for X-ray diffraction were obtained by recrystallisation from nitromethane solution, m.p. 425-427 K.

Refinement
The positional coordinates of the O-bound H atom were located from a difference Fourier map and freely refined along with an isotropic displacement parameter. All the remaining H atoms were placed geometrically in idealized positions and refined using a riding model (including free rotation about the methyl C-C bond), with C-H = 0.95-0.99 Å and U iso (H) = 1.5U eq (C) for methyl groups, or 1.2U eq (C) for other H atoms. Initial refinements demonstrated that the crystal was a nearperfect twin rotated 179 about the [001] direction. The refinement for the twinned data set (R int = 0.0747) converged with R[F 2 > 2(F 2 )], wR(F 2 ), S = 0.0611, 0.2328, 1.115, Flack x = 0.01 (4) (Flack, 1983) by classical fit to all intensities. Deconvolution of the twin yielded a data set that was 91.7% complete to 0.80 Å after the reflections where the overlap was View of the overlay of molecule A (blue) and molecule B (brown).

Figure 4
View of the crystal packing down the c axis. O-HÁ Á ÁO and O-HÁ Á Á hydrogen bonds are shown as red and blue dotted lines (see Table 1 and text).

Figure 5
View of the hydrogen-bonded chain that propagates along the a axis of the crystal. The O-HÁ Á ÁO and O-HÁ Á Á hydrogen bonds are shown as red and blue dotted lines and the view is down the c axis. greater than 0.8 were removed. Crystal data, data collection, and structure refinement details for the full data set with individual twin components are summarized in Table 2.  (Sheldrick, 2015); program(s) used to refine structure: SHELXL2014/6 (Sheldrick, 2015); molecular graphics: SHELXTL (Sheldrick, 2008) and Mercury (Macrae et al., 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008), Mercury (Macrae et al., 2008) and publCIF (Westrip, 2010).

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.