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Properties of perhalogenated {closo-B10} and {closo-B11} multiply charged anions and a critical comparison with {closo-B12} in the gas and the condensed phase

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Abstract

closo-Borate anions [closo-BnXn]2− are part of the most famous textbook examples of polyhedral compounds. Substantial differences in their reactivity and interactions with other compounds depending on the substituent X and cluster size n have been recognized, which favor specific closo-borates for different applications in cancer treatment, chemical synthesis, and materials science. Surprisingly, a fundamental understanding of the molecular properties underlying these differences is lacking. Here, we report our study comparing the electronic structure and reactivity of closo-borate anions [closo-BnXn]2− (X = Cl, Br, I, n = 10, 11, 12 in all combinations) in the gas phase and in solution. We investigated the free dianions and the ion pairs [nBu4N]+[closo-BnXn]2− by gas phase anion photoelectron spectroscopy accompanied by theoretical investigations. Strong similarities in electronic structures for n = 10 and 11 were observed, while n = 12 clusters were different. A systematic picture of the development in electronic stability along the dimension X is derived. Collision induced dissociation shows that fragmentation of the free dianions is mainly dependent on the substituent X and gives access to a large variety of boron-rich molecular ions. Fragmentation of the ion pair depends strongly on n. The results reflect the high chemical stability of clusters with n = 10 and 12, while those with n = 11 are much more prone to dissociation. We bridge our study to the condensed phase by performing comparative electrochemistry and reactivity studies on closo-borates in solution. The trends found at the molecular level are also reflected in the condensed-phase properties. We discuss how the gas phase values allow evaluation of the influence of the condensed phase on the electronic stability of closo-borates. A synthetic method via an oxidation/chlorination reaction yielding [closo-B10Cl10]2− from highly chlorinated {closo-B11} clusters is introduced, which underlines the intrinsically high reactivity of the {closo-B11} cage.

Graphical abstract: Properties of perhalogenated {closo-B10} and {closo-B11} multiply charged anions and a critical comparison with {closo-B12} in the gas and the condensed phase

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Publication details

The article was received on 20 Aug 2018, accepted on 06 Nov 2018 and first published on 07 Nov 2018


Article type: Paper
DOI: 10.1039/C8CP05313H
Citation: Phys. Chem. Chem. Phys., 2019, Advance Article
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    Properties of perhalogenated {closo-B10} and {closo-B11} multiply charged anions and a critical comparison with {closo-B12} in the gas and the condensed phase

    J. Warneke, S. Z. Konieczka, G. Hou, E. Aprà, C. Kerpen, F. Keppner, T. C. Schäfer, M. Deckert, Z. Yang, E. J. Bylaska, G. E. Johnson, J. Laskin, S. S. Xantheas, X. Wang and M. Finze, Phys. Chem. Chem. Phys., 2019, Advance Article , DOI: 10.1039/C8CP05313H

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