The vibrational Raman spectra of some complexes formed between the tetrafluorides of Group VI elements and antimony and arsenic pentafluorides

Abstract

This paper reports the Raman spectra of the complexes SF₄,SbF₅,SeF₄,SbF₅, TeF₄,SbF₅, and SeF₄,AsF₅ in the molten state, the Raman spectra of the salts KSbF₆ in NN-dimethylformamide and KAsF₆ in acetonitrile, the infrared spectra of KSbF₆ and KAsF₆ as Nujol mulls in the range 650–2000 cm.^–1, and the Raman spectrum of liquid arsenic trifluoride. Interpretation of the spectra of KSbF₆ and KAsF₆ leads to assignments for the anions SbF₆ ^– and AsF₆ ^–. The spectra of the molten complexes SF₄,SbF₅, SeF₄,SbF₅, and SeF₄,AsF₅ can be interpreted in terms of the ionic formulations SF₃ ⁺SbF₆ ^–, SeF₃ ⁺SbF₆ ^–, and SeF₃ ⁺AsF₆ ^–. Assignments are made for the SF₃ ⁺ and SeF₃ ⁺ ions, and are compared with those for the isoelectronic PF₃ and AsF₃ molecules. In the case of the complex TeF₄,SbF₅ the situation is less clear and no decision is possible between the two more plausible alternatives of ionisation into distorted ions TeF₃ ⁺ and SbF₆ ^– or a fluorine bridged structure F₃TeFSbF₅. Finally, the stability and degree of ionisation in complexes of this type are discussed in terms of the relative stabilities of the anions and cations that would be formed. Investigations were also made of the systems SF₄/AsF₃, SeF₄/AsF₃, and TeF₄/AsF₃. No evidence for complex formation was obtained.