Critical Influence of Water on the Polymorphism of 1,3-Dimethylurea and Other Heterogeneous Equilibria.

It is shown that the presence of hundreds of ppm of water in 1,3-dimethylurea (DMU) powder led to the large depression of the transition temperature between the two enantiotropically related polymorphic forms of DMU (Form II → Form I) from 58 °C to 25 °C, thus explaining the reported discrepancies on this temperature of transition. Importantly, this case study shows that thermodynamics (through the construction of the DMU-water temperature-composition phase diagram) rather than kinetics is responsible for this significant temperature drop. Furthermore, this work also highlights the existence of a monohydrate of DMU that has never been reported before with a non-congruent fusion at 8 °C.

Metal-organic magnets with large coercivity and ordering temperatures up to 242°C.

Magnets derived from inorganic materials (e.g., oxides, rare-earth-based, and intermetallic compounds) are key components of modern technological applications.

X-ray structural investigation of nonsymmetrically and symmetrically alkylated [1]benzothieno[3,2-b]benzothiophene derivatives in bulk and thin films.

A detailed structural study of the bulk and thin film phases observed for two potential high-performance organic semiconductors has been carried out. The molecules are based on [1]benzothieno[3,2-b]benzothiophene (BTBT) as conjugated core and octyl side groups, which are anchored either symmetrically at both sides of the BTBT core (C8-BTBT-C8) or nonsymmetrically at one side only (C8-BTBT). Thin films of different thickness (8-85 nm) have been prepared by spin-coating for both systems and analyzed by combining specular and grazing incidence X-ray diffraction.

Polymorphism in 2-X-adamantane derivatives (X = Cl, Br).

The polymorphism of two 2-X-adamantane derivatives, X = Cl, X = Br, has been studied by X-ray powder diffraction and normal- and high-pressure (up to 300 MPa) differential scanning calorimetry. 2-Br-adamantane displays a low-temperature orthorhombic phase (space group P212121, Z = 4) and a high-temperature plastic phase (Fm3̅m, Z = 4) from 277.9 ± 1.

From high-temperature orientationally disordered mixed crystals to low-temperature complex formation in the two-component system (CH3)3CBr + Cl3CBr.

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.

Competing intermolecular interactions in the high-temperature solid phases of even saturated carboxylic acids (C10H19O2H to C20H39O2H).

Structural knowledge of the high-temperature phases of saturated carboxylic acids (C(n)H(2n-1)O(2)H) from C(6)H(11)O(2)H to C(23)H(45)O(2)H is now complete. Crystal structures of the high-temperature phases of even acids from decanoic (C(10)H(19)O(2)H) to eicosanoic (C(20)H(39)O(2)H) are reported. The crystal structures of the six compounds were determined from powder X-ray diffraction data following direct space methods and refined by the Rietveld method combined with force field geometry optimization.

From the two-component system CBrCl3+CBr4 to the high-pressure properties of CBr4.

The experimental phase diagram of the CBrCl3+CBr4 system has been determined by means of X-ray powder diffraction and thermal analysis techniques from 200 K to the liquid state. Before melting, the two components have the same orientationally disordered (OD) face-centered cubic phase, and solid-liquid equilibrium is explained by simple isomorphism. The application of multiple crossed isopolymorphism formalism to the low-temperature solid-solid equilibria has enabled the inference of an OD rhombohedral metastable (at normal pressure) phase for CBr4.

Polymorphism and solid-state miscibility in the pentadecanoic acid-heptadecanoic acid binary system.

The pentadecanoic acid-heptadecanoic acid (C(15)H(29)OOH-C(17)H(33)OOH) binary system is dealt with in this article. Combined thermal analysis and X-ray powder diffraction experiments are performed to characterize the polymorphism of the pure compounds and of their mixed samples. In particular, modern methods of crystal structure resolution from powder data (direct space methods) are applied in order to investigate and compare the molecular arrangement within the solid phases of the fatty acids considered.

Multiple crossed isopolymorphism: two-component systems CCl4 +CBr2Cl2 and CBrCl3 + CBr2Cl2; inference of a metastable rhombohedral phase of CBr2Cl2.

The phases diagrams of the two-component systems CCl4 +CBr2Cl2 and CBrCl3 + CBr2Cl2 have been determined by means of X-ray powder diffraction and thermal analysis techniques from the low-temperature ordered phase to the liquid state. The isomorphism relationship between the stable orientationally disordered (OD) face-centered cubic (FCC) phases of CBrCl3 and CBr2Cl2 and the metastable OD FCC phase (monotropic behavior with respect to the OD rhombohedral stable phase) of CCl4 has been put into evidence throughout the continuous evolution of the lattice parameters and the existence of the two-phase equilibrium [FCC + L] for the whole range of composition in both two-component systems. This equilibrium interferes, for the CCl4 +CBr2Cl2 system, with a rhombohedral (R) plus liquid ([R + L]) equilibrium giving rise to a peritectic invariant.

Structures of the high-temperature solid phases of the odd-numbered fatty acids from tridecanoic acid to tricosanoic acid.

Crystal structures of the high-temperature phases of odd-numbered fatty acids (C(n)H(2n-1)OOH) from tridecanoic acid (C(13)H(25)OOH) to tricosanoic acid (C(23)H(45)OOH) are presented in this article. They have been determined from high-quality X-ray powder-diffraction patterns. Two types of high-temperature phases are adopted: one monoclinic A2/a with Z=8 for the fatty acids with n=13 and n=15, denoted as C'', and one monoclinic P2(1)/a with Z=4 for the longer-chain fatty acids, denoted as C'.

Protection of temperature sensitive biomedical products using molecular alloys as phase change material.

In this paper we present an example of the application of molecular alloys for thermal protection of biomedical products during transport or storage. Particularly, thermal protection of blood elements have been considered at different temperatures. All steps from basic research to marketing have been addressed.