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End date: 2024 × Start date: 2020 × DDC: 540 × Publisher: London : RSC Publishing × Subject: Chlorine compounds ×

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    B12X11(H2)−: exploring the limits of isotopologue selectivity of hydrogen adsorption
    (London : RSC Publishing, 2021) Wulf, Toshiki; Warneke, Jonas; Heine, Thomas
    We study the isotopologue-selective binding of dihydrogen at the undercoordinated boron site of B12X11− (X = H, F, Cl, Br, I, CN) using ab initio quantum chemistry. With a Gibbs free energy of H2 attachment reaching up to 80 kJ mol−1 (ΔG at 300 K for X = CN), these sites are even more attractive than most undercoordinated metal centers studied so far. We thus believe that they can serve as an edge case close to the upper limit of isotopologue-selective H2 adsorption sites. Differences of the zero-point energy of attachment average 5.0 kJ mol−1 between D2 and H2 and 2.7 kJ mol−1 between HD and H2, resulting in hypothetical isotopologue selectivities as high as 2.0 and 1.5, respectively, even at 300 K. Interestingly, even though attachment energies vary substantially according to the chemical nature of X, isotopologue selectivities remain very similar. We find that the H–H activation is so strong that it likely results in the instantaneous heterolytic dissociation of H2 in all cases (except, possibly, for X = H), highlighting the extremely electrophilic nature of B12X11− despite its negative charge. Unfortunately, this high reactivity also makes B12X11− unsuitable for practical application in the field of dihydrogen isotopologue separation. Thus, this example stresses the two-edged nature of strong H2 affinity, yielding a higher isotopologue selectivity on the one hand but risking dissociation on the other, and helps define a window of adsorption energies into which a material for selective adsorption near room temperature should ideally fall.
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    Mixed-halide triphenyl methyl radicals for site-selective functionalization and polymerization
    (London : RSC Publishing, 2021) Chen, Lisa; Arnold, Mona; Blinder, Rémi; Jelezko, Fedor; Kuehne, Alexander J. C.
    Derivatives of the stable, luminescent tris-2,4,6-trichlorophenylmethyl (TTM) radical exhibit unique doublet spin properties that are of interest for applications in optoelectronics, spintronics, and energy storage. However, poor reactivity of the chloride-moieties limits the yield of functionalization and thus the accessible variety of high performance luminescent radicals. Here, we present a pathway to obtain mixed-bromide and chloride derivatives of TTM by simple Friedel–Crafts alkylation. The resulting radical compounds show higher stability and site-specific reactivity in cross-coupling reactions, due to the better leaving group character of the para-bromide. The mixed halide radicals give access to complex, and so far inaccessible luminescent open-shell small molecules, as well as polymers carrying the radical centers in their backbone. The new mixed-halide triphenyl methyl radicals represent a powerful building block for customized design and synthesis of stable luminescent radicals.