Strong Lewis and Brønsted Acidic Sites in the Borosulfate Mg<sub>3</sub>[H<sub>2</sub>O→B(SO<sub>4</sub>)<sub>3</sub>]<sub>2</sub>
Philip Netzsch, Regina Stroh, Florian Pielnhofer, Ingo Krossing, Henning A. Höppe
Abstract
Abstract Borosulfates provide fascinating structures and properties that go beyond a pure analogy to silicates. Mg 3 [H 2 O→B(SO 4 ) 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 BF 3 and B(C 6 F 5 ) 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, Mg 3 [H 2 O→B(SO 4 ) 3 ] 2 was characterised by X‐ray diffraction, infrared spectroscopy, thermogravimetric analysis, and density functional theory (DFT) calculations.