Abstract
In the ordered phase, CCl4, CBr4, and CI4 are isostructural crystallizing in a C-centered monoclinic lattice with 32 molecules per unit cell. A close examination of the results of single-crystal structure analyses of CCl4 and CBr4, reveals the exact relationship between the disordered (fcc) and the ordered phases. The molecules, which are regular tetrahedra within the limits of experimental error, lie on sites closely related to, but clearly distinguished from, the lattice points of the ordered fcc phase. The close relationship between these two phases, and the resulting similarity in lattice geometry along different directions in the crystal, leads to an apparent polymorphism between crystals that have grown along different directions. Conflicting data that have been published for ordered CF4 have been resolved and gross similarities between crystalline CF4 and the other CX4 compounds have been described on the basis of similar reduced cells.

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