Abstract
The mesogenic T15 crystallizes in the monoclinic space group P21/c with cell parameters a=12. 165(4)Å, b=17. 542(4)Å, c=9. 054(3)Å, ß=100. 23(2)°, Z=4. The mo-lecule appears in its fully extended form. All molecules are lying parallel. With aid of thermal and x-ray powder analyses two higher temperature solid state phases have been investigated and their unit cell parameters calculated. On the basis of the thermal behavior and the information about the structure of the different phases the mechanism of the phase transition is discussed.