LZS-1, Lanzarote (Canary Island, Spain) lunar (Apollo 14) basaltic soil simulant.

The search for Terrestrial Analogues is essential for the development of future permanent or semi-permanent lunar bases. Terrestrial Analogues are zones where it is possible to probe not only scientific instruments, but also other astronaut capabilities in an environment that is similar to the geological context, geomorphology, mineralogy, geochemistry, etc. that we can find on Mars, the Moon and even asteroids. This work has focused on a multi-analytical characterization of Peñas de Tao geosite basalts in Lanzarote (Canary Islands, Spain). This characterization starts from a field campaign in which 3000 g of basalt rocks were selected. Subsequently, they were analysed by different techniques to determine their composition at a mineralogical and geochemical level, and the results were compared with data from other lunar simulants and from the Apollo 14 mission. After that, a set of petrophysical tests was carried out in order to determine its physical properties and evaluate its capacity as an analogous material for use in situ as a resource for further geological and astrobiological (future lunar habitability) essays.

Dynamic Covalent Properties of a Novel Indolo[3,2-b]carbazole Diradical.

This work describes the synthesis and properties of a dicyanomethylene-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 ) σ-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 monomer ICz-Br reveal that the nature of the one-electron oxidation 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 groups stabilizes the close-lying LUMO and LUMO+1 of (ICz-CN)2 and especially ICz-CN compared to ICz-Br, resulting in a distinctive cathodic response at low overpotentials. Differently from neutral ICz-CN, its radical anion 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 σ-bond in neutral (ICz-CN)2 is cleaved in solution and in the solid-state upon soft external stimuli (temperature, pressure), showing a strong chromism from light yellow to blue-green. Notably, in the solid state, the monomeric diradical species is predominantly formed under high hydrostatic pressure (>1 GPa).

Pressure-Driven Metallization in Hafnium Diselenide.

The quest for new transition metal dichalcogenides (TMDs) with outstanding electronic properties operating under 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 tends 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. Overall, our findings identify 1T-HfSe2 as a new efficient TMD material with potential multipurpose technological applications.

New Multiresponsive Chromic Soft Materials: Dynamic Interconversion of Short 2,7-Dicyanomethylenecarbazole-Based Biradicaloid and the Corresponding Cyclophane Tetramer.

This work reports on a quinodimethane-type molecule, 2,7-dicyanomethylene-9-(2-ethylhexyl)carbazole (1), one of the shortest π-conjugated biradicaloids reported to be stable in solution under ambient conditions. This carbazole-based quinoidal precursor is able to form a macrocyclic σ-bonded tetramer (2). The resolved single-crystal X-ray structure of tetramer 2 shows that four molecules of 1 are linked together through four long (CN)2 C-C(CN)2 bonds (1.631 Å) resulting from coupling of the unpaired electrons in biradicaloid 1. Dynamic interconversion between monomer 1 and cyclophane tetramer 2 is achieved by reversible cleavage and recovery of the four (CN)2 C-C(CN)2 bonds upon soft external stimuli (light absorption, temperature and pressure), which is accompanied by significant color changes. These novel photo-, thermo-, and mechanochromic properties expand the versatility of π-conjugated biradicaloid compounds as novel functional materials that, in combination with spin chemistry and dynamic covalent chemistry, can be relevant in molecular machines, sensors, and switches.

Pressure-induced magnetic switching and linkage isomerism in K0.4Fe4[Cr(CN)6]2.8 x 16 H2O: X-ray absorption and magnetic circular dichroism studies.

The effect of applied pressure on the magnetic properties of the Prussian blue analogue K0.4Fe4[Cr(CN)6]2.8 x 16 H2O (1) has been analyzed by dc and ac magnetic susceptibility measurements. Under ambient conditions, 1 orders ferromagnetically at a critical temperature (T(C)) of 18.5 K. Under application of pressure in the 0-1200 MPa range, the magnetization of the material decreases and its critical temperature shifts to lower temperatures, reaching T(C) = 7.5 K at 1200 MPa. Pressure-dependent Raman and Mossbauer spectroscopy measurements show that this striking behavior is due to the isomerization of some Cr(III)-C[triple bond]N-Fe(II) linkages to the Cr(III)-N[triple bond]C-Fe(II) form. As a result, the ligand field around the iron(II) centers increases, and the diamagnetic low-spin state is populated. As the number of diamagnetic centers in the cubic lattice increases, the net magnetization and critical temperature of the material decrease considerably. The phenomenon is reversible: releasing the pressure restores the magnetic properties of the original material. However, we have found that under more severe pressure conditions, a metastable sample containing 22% Cr(III)-N[triple bond]C-Fe(II) linkages can be obtained. X-ray absorption spectroscopy and magnetic circular dichroism of this metastable sample confirm the linkage isomerization process.

Pseudoatoms and preferred skeletons in crystals.

The generalization of the Zintl-Klemm concept provides a universal formulation of a crystal structure in terms of universal building skeletons formed by Klemm's pseudoatoms: atoms that behave structurally according to their formal total electron charge. An important difference in this novel view is that charge is considered to be transferred, in the strict Zintl's sense, from the donor cations to the building skeleton as a whole, not specifically to a given atom or ion. Although application is restricted to (IV)-(IV) compounds (group 14 structures), the principle seems to be universal and can be applied to understand, to relate and to predict the structure of complex compounds on the basis of more simple structures, e.g. a given AB skeleton provides the building block for A(2)B, AB(2), ABX(m) etc. compounds of a very different nature. The application of such a principle only requires information on the constituent atoms and on the existing phases of the p-block elements (observed under ambient and high-pressure and/or high-temperature conditions). The ideas introduced here demonstrate, for the first time, that a generalization of the Zintl-Klemm concept is possible and that such a generalization helps to establish a univocal link between chemical composition (in terms of pseudoatoms) and the crystalline structures observed experimentally.

Anions in metallic matrices model: application to the aluminium crystal chemistry.

We introduce and discuss an interpretative model of the structure and bonding of inorganic crystals containing metallic elements. The central idea is the conception of the crystal structure of such an inorganic compound as a metallic matrix whose geometric and electronic structures govern the formation and localization of the anions in the lattice. This is the reason for labelling the model anions in metallic matrices (AMM). Taking the AlX3 crystal family (X = F, Cl, OH) as a suitable test-bed class of compounds, we illustrate how this approach gives a direct interpretation of the crystalline structures and explains the variable coordination that Al exhibits in crystalline materials. An exhaustive analysis of the topology of the electron density allows us to provide a quantum-mechanical assessment of the main hypotheses of the AMM model and to uncover, using microscopic arguments, the behavior of anions as chemical pressure agents.

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 square1.2.16H2O (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.