There is currently great interest in replacing the harmful volatile hydrofluorocarbon fluids used in refrigeration and air-conditioning with solid materials that display magnetocaloric, electrocaloric or mechanocaloric effects. However, the field-driven thermal changes in all of these caloric materials fall short with respect to their fluid counterparts. Here we show that plastic crystals of neopentylglycol (CH 3 ) 2 C(CH 2 OH) 2 display extremely large pressure-driven thermal changes near room temperature due to molecular reconfiguration, that these changes outperform those observed in any type of caloric material, and that these changes are comparable with those exploited commercially in hydrofluorocarbons. Our discovery of colossal barocaloric effects in a plastic crystal should bring barocaloric materials to the forefront of research and development in order to achieve safe environmentally friendly cooling without compromising performance.

The high‐spin and low‐spin crystal structures of [Fe(Htrz)2(trz)](BF4) (Htrz = 1H‐1,2,4‐triazole, trz– = deprotonated triazolato ligand) were determined and refined on the basis of X‐ray diffraction data obtained from a high‐quality crystalline powder. Noteworthy differences to the previously reported structural hypothesis are obtained, which includes a revision of the space group to orthorhombic Pnma. Notably, the distinction between the positions of the Htrz and the trz– ligand along the chains reveals their respective roles in the formation of direct interchain interactions. The latter are also mediated by the anions. In addition, the pair‐distribution‐function (PDF) method was applied to investigate the potential modification of the crystal structure by a reduction of the coherent‐domain size from 50 nm to 10 nm. First, the PDF investigation confirms the validity of the crystal structures presented here. Furthermore, in a first approach, it reveals that the crystal structure description remains suitable for the whole range of coherent‐domain sizes investigated.

Magnets derived from inorganic materials (e.g., oxides, rare-earth–based, and intermetallic compounds) are key components of modern technological applications. Despite considerable success in a broad range of applications, these inorganic magnets suffer several drawbacks, including energetically expensive fabrication, limited availability of certain constituent elements, high density, and poor scope for chemical tunability. A promising design strategy for next-generation magnets relies on the versatile coordination chemistry of abundant metal ions and inexpensive organic ligands. Following this approach, we report the general, simple, and efficient synthesis of lightweight, molecule-based magnets by postsynthetic reduction of preassembled coordination networks that incorporate chromium metal ions and pyrazine building blocks. The resulting metal-organic ferrimagnets feature critical temperatures up to 242°C and a 7500-oersted room-temperature coercivity.

Colossal barocaloric effects were observed in four species of plastic crystals, and two displayed the reversibility required for cooling devices.

bode, et al.. Polymorphism of even saturated carboxylic acids from n-decanoic to n-eicosanoic acid.The polymorphism of normal saturated even carboxylic acids from n decanoic to n eicosanoic acid is discussed. Seven crystal modifications, including polymorphs and polytypes, were identified and fully characterized by the combination of calorimetric measurements (DSC) at atmospheric and high pressures, X ray powder diffraction, FT IR spectroscopy and scanning electron microscopy (SEM). All seven crystal forms, including polymorphs and polytypes, are observed at room temperature. Forms A 2 and A super are triclinic, form C is monoclinic and forms E and B show both a monoclinic and an orthorhombic polytype. The triclinic modifications A 2 and A super predominate for acids up to n tetradecanoic acid (C 14 H 27 O 2 H). The orthorhombic and the monoclinic forms predominate for acids from n hexadecanoic (C 16 H 31 O 2 H) up to n eicosanoic acid (C 20 H 39 O 2 H). When the temperature is increased, all the crystal modifications transform irreversibly to the C form. In the first part of this paper, cell parameters for the different forms are given, the observed temperatures and enthalpies of the transitions are reported and the stability of the different forms is discussed. In the second part, we state the main contribution of each technique for the identification and interpretation of the polymorphism of even numbered carboxylic acids.

The polymorphism of bromotrichloromethane (CBrCl 3 ) has been investigated by X-ray powder diffraction and high-pressure density experiments. Phase transitions as a function of temperature and pressure between the different phases have been characterized at normal pressure as well as at high pressures (up to 300 MPa). From the p-V-T diagram (and the derived p-T diagram) the volume variations at the transition points have been calculated and compared with those obtained by means of X-ray powder diffraction characterization. Special attention is given to the lattice symmetry of the orientational disordered phase II, characterized as rhombohedral (a ) 14.639(8) Å, R ) 89.44(1)°at 240.2 K). The existence of a glass transition from the monoclinic low-temperature stable ordered phase (III) to its nonergodic state (associated with the freezing of exchange positions between Cl and Br atoms) is analyzed in terms of the asymmetry of the intermolecular interactions, and a new "fingerprint" for the glass transition is proposed on the basis of the aspherism index. Lattice parameters as a function of temperature were determined in order to build up the thermal expansion tensor.

International audienceThe physico-chemical properties of the levo- and dextrorotatory menthol isomers as well as the corresponding racemic compound were studied using X-ray single-crystal or powder diffraction and differential scanning calorimetry experiments. As a result, the not yet determined crystal structure of DL-menthol was solved. Moreover, the stable and metastable experimental temperature-composition phase diagrams of the L-menthol/D-menthol binary system were determined. The thermodynamic relative stability of the different menthol polymorphs was also established. The present paper provides new physical, chemical and thermodynamic data of L-, D- and DL-menthol and offers new insight into their polymorphism as well as into the levorotatory-dextrorotatory menthol interactions. Both the thermodynamic and crystallographic approaches demonstrate unambiguously that racemic menthol is a racemate

A detailed structural study of the bulk and thin film phases observed for two potential high performance organic semi conductors 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 (C 8 −BTBT−C 8 ) or nonsymmetrically at one side only (C 8 −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. In the case of C 8 −BTBT−C 8 , the known crystal structure obtained from single crystal investigations is observed within all thin films, down to a film thickness of 9 nm. In the case of C 8 −BTBT, the crystal structure of the bulk phase has been determined from X ray powder diffraction data with a consistent matching of experimental and calculated X ray diffraction patterns (Rwp = 5.8%). The packing arrangement of C 8 −BTBT is similar to that of C 8 −BTBT−C 8 , that is, consisting of a lamellar structure with molecules arranged in a "herringbone" fashion, yet with lamellae composed of two head to head (or tail to tail as the structure is periodic) superimposed molecules instead of only one molecule for C 8 −BTBT−C 8 . As for C 8 −BTBT−C 8 ,we demonstrate that the same phase is observed in bulk and thin films for C 8 −BTBT whatever the film thickness investigated.