Stabilization of SF 5 - with Glyme-Coordinated Alkali Metal Cations

The stabilization of complex fluoroanions derived from weakly acidic parent fluorides is a significant and ongoing challenge. The [SF ] anion is recognized as one such case, and only a limited number of [SF ] salts are known to be stable at room temperature. In the present study, glyme-coordinated alkali metal cations (K , Rb , and Cs ) are employed to stabilize [SF ] , which provides a simple synthetic route to a [SF ] salt. The reactivities of KF and RbF with SF are significantly enhanced by complexation with G4, based on Raman spectroscopic analyses. A new room-temperature stable salt, [Cs(G4) ][SF ] (G4 = tetraglyme), was synthesized by stoichiometric reaction of CsF, G4, and SF . The vibrational frequencies of [SF ] were assigned based on quantum chemical calculations, and the shift of the G4 breathing mode accompanying coordination to metal cations was confirmed by Raman spectroscopy. Single-crystal X-ray diffraction revealed that Cs is completely isolated from [SF ] by two G4 ligands and [SF ] is disordered along the crystallographic two-fold axis. Hirshfeld surface analysis reveals that the H···H interaction between two neighboring [Cs(G4) ] moieties is more dominant on the Hirshfeld surface than the interaction between the H atom in glyme molecules and the F atom in [SF ] , providing a CsCl-type structural model where the large and spherical [Cs(G4) ] cations contact each other and the [SF ] anions occupy interstitial spaces in the crystal lattice. The [SF ] anion, combined with [Cs(G4) ] , exhibits a very limited deoxofluorinating ability toward hydroxyl groups in both neat conditions and THF solutions.