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

The reversible structural phase transition accompanied by the doubling of t he unit cell parameter c and a change in the space group is found in the de camethylosmocene crystal Cp-2*Os at a temperature of 243 +/- 5 K. In the hi gh-temperature (HT) phase (space group P2(1)/m, Z = 2), the molecule adopts an eclipsed conformation and lies in the mirror symmetry plane. In the low -temperature (LT) phase (space group P2(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 ph ase at 120 K are described by the deviation of the molecular axis of fivefo ld symmetry by 3.2(2)degrees and the displacement of the center of mass of the molecule by 0.173(2) Angstrom with respect to their positions in the hi gh-temperature phase, and also by the rotation of the Cp* ligands in the sa me direction by 3.0(2)degrees and 5.4(2)degrees, respectively. (C) 2000 MAI K "Nauka/Interperiodica".