Two different silicate/water ice mixtures representing laboratory analogues of interstellar and circumstellar icy grains were produced in the laboratory. For the first time, optical constants, the real and imaginary parts of the complex refractive index, of such silicate/water ice mixtures were experimentally determined in the mid-infrared spectral region at low temperatures. In addition, optical constants of pure water ice and pure silicates were derived in the laboratory.Two sets of constants were compared, namely, "measured" constants calculated from the transmission spectra of silicate/ice samples and "effective" constants calculated from the optical constants of pure silicates and pure water ice samples using different mixing rules (effective medium approaches). Differences between measured and effective constants show that a mixing (averaging) of optical constants of water ice and silicates for the determination of the optical properties of silicate/ice mixtures can lead to incorrect results. Also, it is shown that a part of water ice molecules is trapped in/on silicate grains and does not desorb up to 200 K. Our unique data are just in time with respect to the new challenging space mission, James Webb Space Telescope, which will be able to bring novel detailed information on interstellar and circumstellar grains, and suitable laboratory data are extremely important for the decoding of astronomical spectra.
Reactions of α,β‐unsaturated aromatic thioketones 1 (thiochalcones) with Fe3(CO)12 leading to η4‐1‐thia‐1,3‐diene iron tricarbonyl complexes 2, [FeFe] hydrogenase mimics 3, and the thiopyrane adduct 4 are described. Obtained products have been characterized by X‐ray crystallography and by computational methods. Completely regio‐ and diastereoselective formation of the five‐membered ring system in products 3, containing four stereogenic centers, can be explained by an unprecedented, stepwise (3+2)‐cycloaddition of two thiochalcone molecules mediated by Fe3(CO)12. Quantum chemical calculations aimed at elucidation of the reaction mechanism, suggest that the formal (3+2)‐cycloaddition proceeds via sequential intramolecular radical transfer events upon homolytic cleavage of one carbon‐sulfur bond leading to a diradical intermediate.
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