(1R,2R,5R,6S,9R,10S,13S,14S,18R)-1,6,7,8,9,14,15,16,17,17,18-Undeca-chloro-penta-cyclo-[12.2.1.1.0.0]octa-deca-7,15-diene.

The title compound, C(18)H(13)Cl(11), is an undecachlorinated commercial flame retardant. The asymmetric unit contains two independent half-mol-ecules. The complete mol-ecules are generated by crystallographic inversion symmetry, causing the terminal H atoms and one of the Cl atoms to be disordered equally over two sites in each mol-ecule. The central eight-membered rings are in chair-type conformations. In the crystal structure, there is a single weak inter-molecular C-H⋯Cl hydrogen bond.