From High-Temperature Orientationally Disordered Mixed Crystals to Low-Temperature Complex Formation in the Two-Component System (CH₃)₃CBr + Cl₃CBr

Abstract

The phase diagram of the two-component systems (CH(3))(3)CBr + Cl(3)CBr has been experimentally determined by means of differential scanning calorimetry and X-ray powder diffraction techniques from the low-temperature ordered phases to the liquid state. Before melting, both components have the same orientationally disordered (OD) face-centered cubic (FCC) and rhombohedral (R) phases, and the two-phase equilibria [FCC + L] and [R + FCC] are accounted for by means of the existence of an isomorphic relationship between the OD phases of pure compounds. The thermodynamic assessment of such equilibria enables us to get the excess properties of the involved OD phases and to rationalize the existence of a maximum and a minimum in the [R + FCC] equilibrium on the basis of the contribution of the entropic term in the excess Gibbs energy function. At low temperature, two complexes, (CH(3))(3)CBr:Cl(3)CBr (1:1) and (CH(3))(3)CBr:2Cl(3)CBr (1:2), appear. The structures of 1:1 and 1:2 complexes have been determined to be monoclinic (P2(1)/n, c, Z = 4) and hexagonal (P6(3), Z = 6). Within both "ordered" structures, the Cl(3)CBr entities of the asymmetric unit were found to be disordered so that sites have fractional occupancies of 0.75 and 0.25 for Cl and Br atoms, in the same way that it occurs for the low-temperature monoclinic (C2/c, Z = 32) phase of Cl(3)CBr. Finally, the existence of complexes is connected with the special intermolecular interactions appearing between a methyl group and a halogen, as previously inferred by Calvet et al. [T. Calvet et al. J. Chem. Phys. 1999, 110, 4841].

A Calculation Model of the General Theory of Interaction Potentials for Stoichiometric Lanthanide Type Crystals: Applications to the Cs2KLnCl6 System

“…The thermodynamic cycles of the Born-Haber types have introduced in this article and the calculated values tabulated. Finally, the data employed throughout the course of the current work is given in Appendix-1, where the data given is as follows: 1.1: ionic radius for the lanthanides, 1.2: functions to estimate the lattice parameters as a function of the ionic radius, 1.3: experimental data for the lattice parameters in stoichiometric lanthanide crystals, 1.4:calculated lattice parameters(using the fittings given in 1.2), 1.5: x-parameter crystals, 1.6:electric polarizabilities for a series of ions, 1.7: Born-Mayer parameters, 1.8:Born-Mayer parameters for the pairs (lanthanide-halide), 1.9:ionization potentials for the trivalent lanthanides and 1.10:ionization potentials for the alkaline metals, 1.11:electroafinities for the halide ions, 1.12:bonding energies, 1.13: sublimation heats for metal ions, 1.14: estimated values for and 1.15: estimate of the Born-Mayer for the lanthanide-halide pairs 34–39 .…”

Relationship between the two-component system 1-Br-adamantane + 1-Cl-adamantane and the high-pressure properties of the pure components

“…Even more, the field of phase diagrams involving at least two chemical species, the temperature-composition (T-X) phase diagrams, is generally decoupled from the field of the polymorphic behavior at high pressure. Nevertheless, thermodynamics imposes an univocal relation between the controlled pressure and temperature conditions at which a polymorph should exist and the physical properties derived at normal pressure and, hence, the properties that can be extracted from a temperature-composition phase diagram [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. The other way around also holds, properties derived for stable or metastable phases emerging in the temperature-composition phase diagrams can provide information about the nature of high-pressure phases even when they do not exist as stable phases at normal pressure.…”

Stable, metastable and unstable phases of halogen methane derivatives

“…Halogen methane derivatives, as tetrahalogenomethane compounds (CX n Y m , where n and m = 0, ..., 4; n + m = 4, and X,Y=F, Cl, Br and I) have been investigated by the Group of Characterization of Materials at the Universitat Politècnica de Catalunya during the last years [1]. In spite of the similarity of the molecules, fine tuning interactions give rise to a polymorphic behavior at normal pressure, i.e.…”