title: Phase and glass transitions observed by adiabatic calorimetry of host p-tert-butylcalix[4]arene and guest toluene inclusion crystal, suggesting the progress of the combined order-disorder process of the host-guest molecules.
abstract: Heat capacities of crystalline p-tert-butylcalix[4]arene·toluene host-guest compound were measured in a temperature range between 3 K and 345 K by adiabatic calorimetry. The crystal showed one second-order phase transition at 256.4 K accompanied by wide heat-capacity tails on both the high and low temperature sides and two first-order phase transitions with heat-capacity peaks at 127 K and 139 K. The total entropy of a sequence of the phase transitions was assessed experimentally to be 47 J K(-1) mol(-1), indicating that the number of allowed distinguishable molecular configurations is over 100 in the high-temperature disordered state. Many such distinguishable configurations are understood to be produced by a special intermolecular interaction of C-H···(π-electron) bonds formed between p-tert-butylcalix[4]arene and toluene molecules, and the transitions were interpreted as originating from orientational order-disorder of both the guest toluene molecule and the tert-butyl groups of host arene in their combination.
authors.affiliation: Department of Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology , 2-12-1 O-okayama, Meguro-ku, Tokyo 152-8551, Japan.
authors.forename: Kouhei
authors.initials: K
authors.lastname: Ueda
authors.forename: Masaharu
authors.initials: M
authors.lastname: Oguni