Studies of U(C5H5)3Cl: I-Evidence for structural phase transitions below room temperature

Abstract

AbstractWe have used neutron and X-ray diffraction techniques on both single crystal and polycrystalline samples to examine the symmetry of the unit cell of the organometallic compound uranium tris(cyclopentadienyl)chlorine, U(C5H5)3Cl, as a function of temperature below 300 K. Two phase transitions occur. The first, at 245 K, results in a change of space group but the monoclinic symmetry is retained; the second, at 78 K, results in the material becoming triclinic. Important differences are observed between the results obtained with neutron and X-ray diffraction; the latter fail to show clear evidence for the transition at 78 K. We believe this is a consequence of the different penetration depths of the two radiations. Calorimetric data confirms the presence of the 245 K transition.