Low-temperature heat capacities and derived thermodynamic functions of para-substituted halogen benzenes. 2. p-bromoiodobenzene and p-diiodobenzene

Heat capacity measurements were made on p-bromoiodobenzene and p-diiodobenz ene from 5 K to 380 K and from 5 K to 420 K, respectively. The measurements were used to calculate the entropy and enthalpy values relative to 0 K. Th e enthalpy of melting of p-bromoiodobenzene was found to be (19375 +/- 20) J.mol(-1), and the triple-point temperature, (363.52 +/- 0.01) K. For p-dii odobenzene these values were respectively (22328 +/- 50) J.mol(-1) and (402 .40 +/- 0.05) K. A small solid-solid transition occurs in p-diiodobenzene. The maximum of this transition was measured at 327 K for sublimated materia l and shifted to 322 K for crystallized material. The enthalpy of transitio n was found to be (223 +/- 10) J.mol(-1).