Synthesis and characterization by Raman spectroscopy of AsBr4AsF6; its thermodynamic and kinetic stability and that of related salts

Abstract

The thermodynamically and kinetically unstable salt AsBr₄AsF₆ was prepared by the reaction of stoicheiometric quantities of AsBr₃, Br₂, and AsF₅, and characterized by Raman spectroscopy at –196 °C. It was shown by Raman spectroscopy that AsBr₄AsF₆ decomposes to AsF₃ and Br₂via AsBr₃. The energetics of the formation and decomposition have been estimated, and reaction pathways suggested. Simple estimates of the energetics of the formation of AsBr₄AlBr₄ showed it should have greater stability than that of AsBr₄AsF₆; it was subsequently prepared but shown to be in equilibrium at room temperature with AsBr₃, Br₂, and AsBr₄Al₂Br₇. The differences in thermodynamic stability of AsCl₄AsF₆ and AsBr₄AsF₆ have been accounted for, and reasons for the kinetic instability of AsBr₄AsF₆ proposed.