The crystal structure of ThCl₄ and UCl₄

The crystal structure of ThCl₄ and of UCl₄ has been determined from X-ray powder diffraction photographs. The structures are isomorphous. The lattice is body-centered tetragonal; the space group symmetry is D-I4/amd. There are four molecules in the unit cell. The cell dimensions are as follows: ThCl₄ a₁ = 8.473 ± 0.003 A., a₃ = 7.468 ± 0.003 A., _calc. = 4.60 g.cm.^-3; UCl₄ a₁ = 8.296 ± 0.009 A., a₃ = 7.487 ± 0.009 A., _calc. = 4.866 g.cm.^-3. Positions have been found for the atoms such that the calculated intensities are in good agreement with observations. Each metal atom is co-ordinated to eight chlorines. Four chlorines are at significantly smaller distances than the remaining four, indicating that the bonds tend towards covalency.