The two solid phases of chlorodifluoromethane

The crystal structure of the two phases of chlorodifluoromethane (CHClF2) were determined at 70 K and 10 K using Rietveld refinement of neutron powder profiles. The upper phase is tetragonal P42/n (C4 4 h) with eight molecules in the unit cell occupying general positions. The lattice constants are a = 10•3711(1) Å and c = 5•5915(2) Å. The lower phase is monoclinic P112/n (C2 4 h) with eight molecules in the unit cell with dimensions a = 10•1106(2), b = 10•4830(2), c = 5•5868(2) Å and γ = 90•319(2)°. The asymmetric unit has two molecules in general positions. The phase transition is of a displacive type but there are no large changes in the molecular positions or orientations at the transition.