Phase Transition of Solid Hexabromoethane

The phase transition point of solid hexabromoethane was found at 177°C, above which the crystal is a body centered cubic lattice with two molecules in a unit cell, having a cell length of 7.80 Å at 185°C. From an analysis of entropy change, it seems that random orientations of the molecular axis would occur at the transition point. The influence of halogen substitution is discussed. It was concluded that the phase transition will be dominated mainly by the geometrical properties of the molecules.