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Strong Lewis and Brønsted Acidic Sites in the Borosulfate Mg3 [H2 O→B(SO4 )3 ]2
Philip Netzsch1, Regina Stroh2, Florian Pielnhofer3
1Lehrstuhl für Festkörperchemie, Universität Augsburg, Universitätsstrasse 1, 86159, Augsburg, Germany.
Abstract:
Borosulfates provide fascinating structures and properties that go beyond a pure analogy to silicates. Mg3 [H2 O→B(SO4 )3 ]2 is the first borosulfate featuring a boron atom solely coordinated by three tetrahedra. Thus, the free Lewis acidic site forms a Lewis acid-base adduct with a water molecule. This is unprecedented for borosulfate chemistry and even for borates. Quantum chemical calculations on water exchange reactions with BF3 and B(C6 F5 )3 revealed a higher Lewis acidity for the borosulfate anion. Moreover, proton exchange reactions showed a higher Brønsted acidity than comparable silicates or phosphates. Additionally, Mg3 [H2 O→B(SO4 )3 ]2 was characterised by X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, and density functional theory (DFT) calculations.
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