MOLECULAR-INTERACTIONS AND PACKING IN MOLECULAR ALLOYS BETWEEN NONISOMORPHOUS PLASTIC PHASES

The experimental two-component phase diagram for the plastic crystals tris(hydroxymethyl)aminomethane (TRIS) and pentaerythritol (PE) has be en established from 293 K to the liquid state using thermal analysis a nd X-ray powder diffraction at several temperatures, The miscibility a nd the intermolecular interactions of the mentioned system and other r elated binary systems formed from compounds which present also nonisom orphous plastic phases are discussed on the basis of the steric condit ions (similarity of the unit-cell dimensions and of the size and shape of the molecules) and of the other factors governing the structural a rrangements such as the effects of the orientational disorder. The evo lution of the packing coefficient as a function of the composition in each two-component system is analyzed to attain further understanding of the intermolecular interactions in orientationally disordered pure and mixed crystals. (C) 1996 Academic Press, Inc.