Solid state phase transitions and molecular reorientation in o r t h o- and p a r a-carborane: An isomer effect

The proton nuclear spin–lattice relaxation times at 30 MHz have been measured for ortho- and para-carborane between 170 and 310 K and between 210 and 320 K, respectively. Para-carborane undergoes solid–solid transitions at about 300 and 238 K while the ortho isomer shows only one transition at about 265 K. The details of the phase transitions are discussed and molecular reorientation in the isomers is compared.