1,4-Bis(4-chlorophenylseleno)-2,5-dimethoxybenzene

The title compound, C20H16Cl2O2Se2, utilizes the symmetry of the crystallographic inversion center. Molecular chains are formed through symmetric C—H⋯Cl interactions around inversion centers, mimicking the commonly observed symmetric hydrogen-bonded dimer pattern often found in carboxylic acids.

The title compound, C 20 H 16 Cl 2 O 2 Se 2 , utilizes the symmetry of the crystallographic inversion center. Molecular chains are formed through symmetric C-HÁ Á ÁCl interactions around inversion centers, mimicking the commonly observed symmetric hydrogen-bonded dimer pattern often found in carboxylic acids.

Structure Reports Online
The molecular packing arrangement is dominated by molecular chains (see Fig. 2) formed by cyclic C ar -H···Cl interactions [H7···Cl i = 2.96 Å, C7-H7···Cl i = 166.0°; symmetry code: (i) 2 -x,1 -y,1 -z] around an inversion center leading to a pattern, which highly resembles the cyclic hydrogen-bonded dimers frequently observed in carboxylic acids. The C ar -H···Cl type of cyclic interaction found in 1 has also been observed in other compounds having a p-chlorosubstituted phenyl group, e.g. in the structure of racemic p-chlorophenoxypropionic acid, where the distance H···Cl is 2.92 Å [C-H···Cl 175°]. The chains are stacked such that the π-π interactions between the phenelseleno groups and between the benzene rings along the diagonal of the b and c-axes, respectively. Due to the chain formation in 1 the packing arrangement is rather different from the pattern found in DMPSB, where interactions with chlorine cannot be formed.

Experimental
Crystals suitable for an X-ray diffraction experiment were obtained by slow crystallization from hot toluene.

Refinement
Hydrogen atoms of (1) were found in the difference Fourier map. All hydrogen atoms were treated as riding atoms with C-H distances of 0.95 for C ar and 0.98 for the C Me . Isotropic displacement parameters for all H atoms were constrained to 1.2U eq of the connected non-hydrogen atom (1.5U eq for Me groups). Fig. 1. Thermal elipsoid plot of (1) including labelling of the atoms. The displacement ellipsoids are drawn at the 50% probability level. H atoms are shown as spheres with an arbitrary radii.  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 Rfactors(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