Stabilization of SF5 – with Glyme-Coordinated Alkali Metal Cations

• Published in: Inorganic chemistry 2018-12, Vol.57 (23), p.14882-14889
• Main Authors: Matsumoto, Kazuhiko, Haruki, Yuki, Sawada, Shunsuke, Yamada, Shigeyuki, Konno, Tsutomu, Hagiwara, Rika
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.8b02655

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 are 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 two-fold 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 toward hydroxyl groups in both neat conditions and THF solutions.