A Study on the phase transition in decamethylosmocene crystal over a wide temperature range

Abstract

The reversible structural phase transition accompanied by the doubling of the unit cell parameter c and a change in the space group is found in the decamethylosmocene crystal C Os at a temperature of 243 ∠ 5 K. In the high-temperature (HT) phase (space group P 2 1 / m , Z = 2), the molecule adopts an eclipsed confor- mation and lies in the mirror symmetry plane. In the low-temperature (LT) phase (space group P 2 1 / c , Z = 4), the molecule occupies the general position with a small rotation of the ligands. The structural transformations from the high-temperature phase into the low-temperature phase at 120 K are described by the deviation of the molecular axis of fivefold symmetry by 3.2(2) i and the displacement of the center of mass of the molecule by 0.173(2) A with respect to their positions in the high-temperature phase, and also by the rotation of the Cp * ligands in the same direction by 3.0(2) i and 5.4(2) i , respectively. © 2000 MAIK "Nauka/Interperiodica". p 2 *