CRYSTAL-STRUCTURES, PHASE-TRANSITIONS, AND HYDROGEN BONDINGS IN PENTABROMOPHENOL, PENTACHLOROPHENOL, AND THEIR MIXED-CRYSTALS

Pure pentachlorophenol, pentabromophenol, and their mixed crystal cont aining 12 mol% of pentabromophenol are studied by differential scannin g calorimetry (DSC), X-ray diffraction, and near-IR spectroscopy. The resolved crystal structure of pentabromophenol is P2(1) with a = 0.823 8(8) nm, b = 0.4021(9) nm, c = 1.4822(8) nm, beta = 95.82(6)-degrees, Z = 2. The mixed crystal is isostructural with pentachlorophenol. Temp eratures and enthalpies of phase transitions occurring in the studied crystals above room temperature are measured. Inter- and intramolecula r hydrogen bondings and free OH groups are monitored by the overtone b and of the OH stretching vibration measured as a function of temperatu re and time. The metastable phase occurrence is also studied with X-ra y powder diffraction and dilatometry.