Dihalo bismuth cations: unusual coordination properties and inverse solvent effects in Lewis acidity

Abstract

A series of well-defined cationic hepta-coordinate bismuth halides [BiX₂(py)₅][B(3,5-(CF₃)₂-C₆H₃)₄] (X = Cl, Br, I), stabilized only by substitutionally labile solvent molecules, were synthesized and fully characterized. Their apparent D_5h symmetry with a lone pair at the central atom is unprecedented for main group compounds. The potential of BiX₃ to show unexpectedly high Lewis acidities in moderately polar solvents is likely due to the formation of [BiX₂(solv)₅]⁺ and related ionic species.