Solid-phase chemiluminescent reaction of Eu2(SO4)3 with XeF2 as a possible source of the Eu(IV) highest oxidation state

Abstract

The highly exothermic solid-phase interaction of anhydrous europium (III) sulfate polycrystalline powder with xenon difluoride was found to be a potential source of the highest oxidation state (HOS) of europium, Eu4+. The reaction is accompanied by chemiluminescence (CL) in the visible spectral region and proceeds spontaneously at room temperature for ​~ ​20 ​h. Several photon emitters are established and identified, namely, atomic Xe and single-ionized xenon Xe+, emitting in the wavelength range 420–700 ​nm, as well as the electronically excited ion Eu3+ (590–700 ​nm). Absorption with a maximum of ~340 ​nm is registered in the diffuse reflectance spectrum of the reaction mixture during first few minutes of the reaction. This signal is tentatively assigned to the HOS of europium (+4). The reaction mechanism is proposed which includes a) Eu3+-assisted decomposition of xenon difluoride leading to atomic fluorine as well as highly reactive intermediates XeF+ and Xe+; b) oxidation of Eu3+ ion to the HOS by the latter; c) generation of excited species in the reduction stages followed by CL: Xe2+(Xe+) → Xe0 (blue-green emission) and Eu4+ → Eu3+ (red emission), sulfate environment is considered as the reductant; d) the F• ​+ ​SO4•- interaction and partial replacement of sulfate ligands with fluoride and fluorosulfate anions in the coordination sphere of the europium ion. Theoretical calculations using composite methods suggest the proposed mechanism and demonstrate the thermodynamic probability of ozone formation in the studied reaction, which was detected by the characteristic UV absorption band.