4,5-Dibromo-2,7-di-tert-butyl-9,9-dimethyl-9H-thioxanthene

In the title compound, C23H28Br2S, the thioxanthene unit is twisted, showing a dihedral angle of 29.3 (5)° between the benzene rings. When projected along [001], the packing shows two types of channels. The crystal studied was a racemic twin.

In the title compound, C 23 H 28 Br 2 S, the thioxanthene unit is twisted, showing a dihedral angle of 29.3 (5) between the benzene rings. When projected along [001], the packing shows two types of channels. The crystal studied was a racemic twin.

R. Morán Comment
Thioxanthenes are very valuable building blocks for several purposes. Specifically, the compound described in this paper has been used as a starting material in the preparation of rigid ligands for different transitions metals as Ni, Pd, Fe, etc (Emslie et al., 2008).
The molecules in the cell unit are orientated in opposite directions forming parallel sheets along the a and b axes, which intersect perpendicularly originating two types of channels A and B, as is shown in Fig. 2 and 3.

Experimental
The title compound was obtained from thioxanthone according to a method described previously (Emslie et al., 2006).

Refinement
The hydrogen atoms were positioned geometrically, with C-H distances constrained to 0.93 Å (aromatic CH) and 0.96 Å (methyl CH 3 ) and refined in riding mode with U iso (H) = xUeq(C), where x =1.5 for methyl H atoms and x = 1.2 for all other atoms.  Molecular structure of C 23 H 28 Br 2 S. Displacement ellipsoids are drawn at the 50% probability level. Hydrogen atoms are shown as spheres of arbitrary radius.

Figure 2
Crystal packing of C 23 H 28 Br 2 S view along c-axis, showing two kind of channels.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq