Pressure-Induced Conversion of a Paramagnetic FeCo Complex into a Molecular Magnetic Switch with Tuneable Hysteresis.

A key challenge in the design of magnetic molecular switches is to obtain bistability at room temperature. Here, we show that application of moderate pressure makes it possible to convert a paramagnetic FeIII 2 CoII 2 square complex into a molecular switch exhibiting a full dia- to paramagnetic transition: FeII CoIII ⇔ FeIII CoII . Moreover, the complex follows a rare behavior: the higher the pressure, the broader the magnetic hysteresis. Thus, the application of an adequate pressure allows inducing a magnetic bistability at room temperature with predictable hysteresis width. The structural studies at different pressures suggest that the pressure-enhanced bistability is due to the strengthening of intermolecular interactions upon pressure increase. An original microscopic Ising-like model including pressure effects is developed to simulate this unprecedented behavior. Overall, this study shows that FeCo complexes could be very sensitive piezo switches with potential use as sensors.

The degradation of organic compounds impacts the crystallization of clay minerals and vice versa.

Expanding our capabilities to unambiguously identify ancient traces of life in ancient rocks requires laboratory experiments to better constrain the evolution of biomolecules during advanced fossilization processes. Here, we submitted RNA to hydrothermal conditions in the presence of a gel of Al-smectite stoichiometry at 200 °C for 20 days. NMR and STXM-XANES investigations revealed that the organic fraction of the residues is no longer RNA, nor the quite homogeneous aromatic-rich residue obtained in the absence of clays, but rather consists of particles of various chemical composition including amide-rich compounds. Rather than the pure clays obtained in the absence of RNA, electron microscopy (SEM and TEM) and diffraction (XRD) data showed that the mineralogy of the experimental residues includes amorphous silica and aluminosilicates mixed together with nanoscales phosphates and clay minerals. In addition to the influence of clay minerals on the degradation of organic compounds, these results evidence the influence of the presence of organic compounds on the nature of the mineral assemblage, highlighting the importance of fine-scale mineralogical investigations when discussing the nature/origin of organo-mineral microstructures found in ancient rocks.

Pressure Control of Cuprophilic Interactions in a Luminescent Mechanochromic Copper Cluster.

For the development of applications based on mechanochromic luminescent materials, a comprehensive study of the mechanism responsible for the emission changes is required. We report the study of a mechanochromic copper iodide cluster under hydrostatic pressure, which allows control of crystal packing via modification of the intermolecular interactions. In situ single-crystal powder X-ray diffraction analysis and emission measurements under pressure permit one to establish a direct correlation between the molecular structure and luminescence properties and, in particular, to demonstrate that cuprophilic interactions are responsible for the stimuli-responsive luminescence properties of such multinuclear coordination compounds.