3,4′,5-Trichlorobiphenyl-4-yl 2,2,2-trichloroethyl sulfate

Crystals of the title compound, C14H8Cl6O4S, are twinned by inversion, with unequal components [0.85 (3):0.15 (3)]. The asymmetric unit contains two independent molecules that are related by a pseudo-inversion center. The Car—O [1.393 (9) and 1.397 (9) Å] and ester S—O bond lengths [1.600 (5) and 1.590 (5) Å] of both molecules are comparable to the structurally related 2,3,5,5-trichlorobiphenyl-4-yl 2,2,2-trichloroethyl sulfate. The dihedral angles between the benzene rings in the two molecules are 37.8 (2) and 35.0 (2)°.

Only limited structural information about sulfate mono-and diesters of hydroxylated PCBs is available to support structure-activity or structure-property relationship studies. Here we report the structure of the title compound, a biphenyl-4-yl 2,2,2-trichloroethyl sulfate with two chlorine substituents ortho to the sulfate group, to contribute to the number of available crystal structures.
The two independent molecules of the title compound in the asymmetric unit are related by a pseudo-inversion center.
The dihedral angle of the biphenyl moiety of PCB derivatives is a structural parameter associated with the affinity of PCB derivatives for cellular target molecules. The two molecules of the title compound have solid state dihedral angles of 37.8 (2)° and 35.0 (2)°. Similarly, structurally related biphenyl-4-yl 2,2,2-trichloroethyl sulfates have dihedral angles ranging from 4.9° to 41.8° in the solid state (Li et al., 2008;Li et al., 2010a;Li et al., 2010c). The fact that biphenyl-4-yl 2,2,2-trichloroethyl sulfates without ortho chlorine substituents adopt a range of dihedral angles can be explained by crystal packing effects, which force the biphenyl moiety to adopt an energetically less favorable conformation in the solid state.

Experimental
The title compound was synthesized from 3,4′,5-trichlorobiphenyl-4-ol and 2,2,2-trichloroethyl sulfonyl chloride using 4dimethylaminopyridine as catalyst as reported previously (Li et al., 2008). Crystals suitable for X-ray diffraction analysis were obtained by slow evaporation of a methanolic solution. Refinement H atoms were found in difference Fourier maps and subsequently placed in idealized positions with constrained distances of 0.99 Å (R 2 CH 2 ), 0.95 Å (C sp2 H), and with U iso (H) values set to either 1.2U eq or 1.5U eq (RCH 3 , OH) of the attached atom.
The two independent molecules are related by a pseudo-inversion centre, which results in large correlations between the displacement parameters. In order to ensure satisfactory refinement, the displacement parameters of equivalent atoms in each molecule were constrained to be the same using the EADP command of SHELXL97.  View of the title compound showing the atom-labeling scheme. Displacement ellipsoids are drawn at the 50% probability level.  Conventional R-values R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-values based on F 2 are statistically about twice as large as those based on F, and R-values based on ALL data will be even larger.