The stabilization of complex fluoroanions derived from weakly acidic parent fluorides is a significant and ongoing challenge. The [SF5] − anion is recognized as one such case and only a limited number of [SF5] − 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 [SF5] − , which provides a simple synthetic route to a [SF5] − salt. The reactivities of KF and RbF with SF4 is significantly enhanced by complexation with G4, based on Raman spectroscopic analyses. A new room-temperature stable salt, [Cs(G4)2][SF5] (G4 = tetraglyme), was synthesized by stoichiometric reaction of CsF, G4, and SF4. The vibrational frequencies of [SF5] − 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 [SF5] − by two G4 ligands and [SF5] − is disordered along the crystallographic twofold axis. Hirshfeld surface analysis reveals that the H•••H interaction between two neighboring [Cs(G4)2] + moieties is more dominant on the Hirshfeld surface than the interaction between the H atom in glyme molecules and the F atom in [SF5] − , providing a CsCl-type structural model where the large and spherical [Cs(G4)2] + cations contact each other and the [SF5] − anions occupy interstitial spaces in the crystal lattice. The [SF5] − anion, combined with [Cs(G4)2] + , exhibits a very limited deoxofluorinating ability towards hydroxyl groups in both neat conditions and THF solutions.