Pressure-Tuning of Magnetism and Linkage Isomerism in Iron(II) Hexacyanochromate

A pressure-induced linkage isomerization of the cyanide anion has been observed in single crystals of a chromium(III)−iron(II) Prussian blue analogue of formula K0.4Fe4[Cr(CN)6]2.8□1.2·16H2O (1). Upon application of pressure in the 0−1200 MPa range, the cyanide ligand rotates and becomes C-bonded to the iron(II) cations, leading to a stabilization of their diamagnetic low-spin states. The result is a decrease of magnetization and magnetic ordering temperatures from TC = 19 K at ambient pressure to 13 K at 1200 MPa. The initial magnetic properties can be restored on pressure release. The reversible movement of cyanide in the solid state can be exploited as a switch of the magnetic interaction at the molecular level.We thank J. M. Martínez-Agudo for the magnetic measurements. Financial support from the Ministerio de Educación y Ciencia (Project MAT2004-03849 and Programa “Ramón y Cajal” to F.M.R.) and Generalitat Valenciana is also acknowledged.S

Pressure-Driven Metallization in Hafnium Diselenide

The quest for new transition metal dichalcogenides (TMDs) with outstanding electronic properties operating at ambient conditions draws us to investigate the 1T-HfSe2 polytype under hydrostatic pressure. Diamond anvil cell (DAC) devices coupled to in- situ synchrotron X-ray, Raman and optical (VIS-NIR) absorption experiments along with density functional theory (DFT) based calculations prove that: (i) bulk 1T-HfSe2 exhibits strong structural and vibrational anisotropies, being the interlayer direction especially sensitive to pressure changes, (ii) the indirect gap of 1T-HfSe2 trend to vanish by a -0.1 eV/GPa pressure rate, slightly faster than MoS2 or WS2, (iii) the onset of the metallic behavior appears at Pmet ~10 GPa, which is to date the lowest pressure among common TMDs, and finally (iv) the electronic transition is explained by the bulk modulus B0-Pmet correlation, along with the pressure coefficient of the band gap, in terms of the electronic overlap between chalcogenide p-type and metal d-type orbitals

SuperCam Calibration Targets: Design and Development

SuperCam is a highly integrated remote-sensing instrumental suite for NASA’s Mars 2020 mission. It consists of a co-aligned combination of Laser-Induced Breakdown Spectroscopy (LIBS), Time-Resolved Raman and Luminescence (TRR/L), Visible and Infrared Spectroscopy (VISIR), together with sound recording (MIC) and high-magnification imaging techniques (RMI). They provide information on the mineralogy, geochemistry and mineral context around the Perseverance Rover. The calibration of this complex suite is a major challenge. Not only does each technique require its own standards or references, their combination also introduces new requirements to obtain optimal scientific output. Elemental composition, molecular vibrational features, fluorescence, morphology and texture provide a full picture of the sample with spectral information that needs to be co-aligned, correlated, and individually calibrated. The resulting hardware includes different kinds of targets, each one covering different needs of the instrument. Standards for imaging calibration, geological samples for mineral identification and chemometric calculations or spectral references to calibrate and evaluate the health of the instrument, are all included in the SuperCam Calibration Target (SCCT). The system also includes a specifically designed assembly in which the samples are mounted. This hardware allows the targets to survive the harsh environmental conditions of the launch, cruise, landing and operation on Mars during the whole mission. Here we summarize the design, development, integration, verification and functional testing of the SCCT. This work includes some key results obtained to verify the scientific outcome of the SuperCam system

Dynamic covalent properties of a novel indolo[3,2-b]carbazole diradical

This work describes the synthesis and properties of adicyanomethylene-substituted indolo[3,2-b]carbazole diradical ICz-CN. This quinoidal system dimerises almost completely to (ICz-CN)2,which contains two long C(sp3)@ C(sp3) s-bonds between the dicyanomethylene units. The minor open-shell ICz-CN component in the solid-state mixture was identified by EPR spectroscopy.Cyclic voltammetry and UV–visible spectroelectrochemical data, as well as comparison with reference monomerICz-Br reveal that the nature of the one-electronoxidation of (ICz-CN)2 at ambient temperature and ICz-CN at elevated temperature is very similar in all these compounds due to the prevailing localization of their HOMO on the ICz backbone. The peculiar cathodic behaviour reflects the co-existence of (ICz-CN)2 and ICz-CN. The involvement of the dicyanomethylene groupsstabilizes the close-lying LUMO and LUMO+1of(ICz-CN)2 and especially ICz-CN comparedtoICz-Br,resulting in ad istinctive cathodic response at low overpotentials. Differently from neutralICz-CN, its radicalanion and dianion are remarkably stable under ambient conditions. The UV/Vis(–NIR) electronic transitions in parent (ICz-CN)2 and ICz-CN and their different redox forms have been assigned convincingly with the aid of TD-DFT calculations. The s-bond in neutral(ICz-CN)2 is cleaved in solution and in the solid-state upon soft external stimuli (temperature, pressure), showing astrong chromism from light yellow to blue–green. Notably,inthe solid state, the monomeric diradical species is predominantly formed under high hydrostatic pressure (>1GPa)