Temperature dependence of the Raman spectrum of the plastic solid carborane p-C2B8H10: Investigation of the phase transitions, orientational disorder and the behaviour of the so-called ‘background’

The temperature dependence of the Raman spectrum of the plastic solid carborane p-C2B8H10 was studied in the range 15–470 K. Unlike the icosahedral carboranes C2B10H12, this ‘stretched’ carborane has only one plastic phase, probably with anisotropic reorientations. A phase transition to an ordered crystal takes place at 188 K. In a sealed capillary the substance melts at 433 K. The Raman spectrum of p-C2B8H10, originally having no background, acquired the background after the sample had been repeatedly heated and cooled. It was found that the background intensity depends on the thermal prehistory of the sample; it slowly diminishes on heating, and several degrees below the melting point the background disappears completely and re-emerges in the spectrum of the melt.