Ligand-assisted excitation of Eu(III) during interaction of Eu(FOD)3 with xenon difluoride in acetonitrile solution

Abstract

The interaction of tris(1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octanedionato)europium(III), (Eu(FOD)₃), with xenon difluoride in acetonitrile solution was found to be accompanied by chemiluminescence (CL). The kinetic curve of CL at a ratio of reagents Eu³⁺/XeF₂ of 1:2 has a complex form; an initial rapid decrease is replaced by an increase in CL intensity, the maximum of which is reached approximately 10 min after the start of the reaction. Next, an exponential decay of the CL intensity is observed over several tens of minutes. The CL spectrum is located in the wavelength range 400–750 nm and corresponds to the emission of an electronically excited europium (III) ion coordinated with FOD and fluoride ion. Spectral methods were used to identify the reaction products – europium (III) fluoride in the sediment and oxygen difluoride in the gas phase. A mechanism for chemiexcitation of europium(III) has been proposed, including: 1) acceptance of fluorine anion from the XeF₂ molecule by europium ion with the formation of active intermediate XeF⁺; 2) oxidative fluorination of the ligand, which is initiated by the interaction of oxygen atom of the FOD ligand with XeF⁺ cation and ends with the formation of oxygen difluoride and the electronically excited product P*, presumably a fluorinated ketone; 3) non-radiative transfer of excitation energy from P* to the europium ion within its coordination sphere, followed by its radiative deactivation.