The Influence of 4f Orbital Excitation in Eu(Fod)3 on Complexation with Sulfones in Benzene Solutions

Complexation of sulfones (S) with the -diketonate Eu(Fod)₃ (Fod–heptafluorodimethyloctanedione) in the ground and excited electronic states in benzene solutions was studied. The stability constants and thermodynamic parameters for the formation of complexes Eu(Fod)₃ · S in the ground state (K, H₀, S₀) and Eu(Fod)₃^* · S in the excited state (K*, H₀^*, S₀^*) were determined. The excitation of f–f transitions of Eu(III) was found to enhance the stability of Eu(Fod)₃ · S complexes, apparently due to an increase in the acceptor ability of the Eu(III) chelate. This fact confirms the involvement of the 4f orbital in the chemical bond formation. The compensation effect was observed for the thermodynamic parameters: S₀ = (2.9 ± 0.3) × 10^–3H₀ + (35.0 ± 4.0) in the ground and S₀^* = (3.3 ± 0.3) × 10^–3H₀^* + (49.0 ± 5.0) in the excited states of Eu(Fod)₃. It was shown that electronic excitation of the 4f orbital of Eu(Fod)₃ influences isotopic effects in complexation with sulfolanes.