Clathrate formation and phase equilibria in the thiourea-bromoform system

Abstract

Phase equilibria in the thiourea (host)-bromoform (guest) binary system were studied by physicochemical analysis methods over the temperature range 270–455 K. The stoichiometry and stability region were determined for the channel-type compound CHBr3 · 2.40(2)(NH2)2CS; the compound was observed for the first time. When heated, the clathrate incongruently decomposed at 424.0 ± 0.8 K to rhombic thiourea and the guest component. The solubility isotherm of the thiourea-bromoform-acetic acid system was studied to find that the compound was thermodynamically stable at 293 K over the range of guest component concentrations 100–35 wt %. A decrease in its content in an equilibrium mother liquor resulted in the appearance of X-ray diffraction reflections of the initial host α polymorph. Rhombohedral cell parameters were determined (space group R-3c, a = 15.89(1) A, c = 12.40(1) A, V = 2711(6) A3, d calcd = 2.000 g/cm3, and d expt = 1.98(2) g/cm3). The mode of packing of bromoform molecules was compared with the organization of the guest subsystem in inclusion compounds formed by the substances studied.