The `super acid' BF<sub>3</sub>H<sub>2</sub>O stabilized by 1,4-dioxane: new preparative aspects and the crystal structure of BF<sub>3</sub>H<sub>2</sub>O·C<sub>4</sub>H<sub>8</sub>O<sub>2</sub>
Acta crystallographica. Section E, Crystallographic communications