Neutron structure refinement of orthorhombic hexachloroethane

The structure of orthorhombic hexachloroethane has been refined at 294 and 140 K. At room temperature 983 symmetry-independent reflections were measured on a four-circle neutron diffractometer. The final R(F) was 0..066 including an isotropic extinction parameter. At 140 K 793 symmetry-independent reflections refined to R(F) = 0-056. The temperature parameters have been analyzed in terms of the tensors T, L and S describing the rigid-body movement of the C2C16 molecule. The temperature variation of the T and L tensors can be understood with the assumption of strong anharmonic contributions. There is, however, no indication of rotational disorder in the orthorhombic phase.