The Elusive Fluoropolysulfates [FS 2 O 6 ] – and [FS 3 O 9 ] – , a New Class of Weakly Coordinating Anions

The isolation and structural characterization of the fluorodi‐ and fluorotrisulfate anions, [FS 2 O 6 ] – and [FS 3 O 9 ] – are reported. The [FS 2 O 6 ] – anion has been obtained from reactions of SO 3 with XeF 2 in the presence of PbF 2 as the salt Pb[FSO 3 ][FS 2 O 6 ] (triclinic, P , Z = 2, a = 508.65(3), b = 909.67(5), c = 969.67(5) pm, α = 89.494(2)°, β = 77.373(2)°, γ = 76.466(2)° and V = 424.99(4) Å 3 ). The [FS 3 O 9 ] – ion forms in the reaction of K[FSO 3 ] with SO 3 at room temperature as the potassium salt K[FS 3 O 9 ] (monoclinic, P 2 1 / c , Z = 4, a = 1048.69(8), b = 786.39(6), c = 969.58(7) pm, β = 90.431(2)° and V = 799.6(1) Å 3 ). The use of the [FS 3 O 9 ] – ion as a weakly coordinating anion was demonstrated with the isolation of [Se 4 ][FS 3 O 9 ] 2 (monoclinic, P 2 1 / n , Z = 2, a = 719.2(1), b = 1576.0(2), c = 897.7(1) pm, β = 113.015(5)° and V = 936.5(2) Å 3 ), obtained from the reaction of selenium, SO 3 and XeF 2 at 80°C. We investigated the anions quantum chemically concerning their molecular electrostatic potentials and the electronic energies of formation. The non–covalent interactions in [Se 4 ][FS 3 O 9 ] 2 were analysed using Quantum Theory of Atoms in Molecules (QTAIM) and Natural Bond Orbital Analysis (NBO).