Unexpected Findings in a Simple Metathesis Reaction of Europium and Ytterbium Diiodides with Perfluorinated Mercaptobenzothiazolates of Alkali Metals

In the search for new f–d luminescent complexes of Eu(II) and Yb(II) the metathesis reactions of diiodides of these metals with perfluorinated 2-mercaptobenzothiazolates of alkali metals were studied. It has been found that the reactions of LnI 2 (THF) 2 (Ln = Eu, Yb) with K(mbt F ) (mbt F = perfluorinated 2-mercaptobenzothiazolate anion) in DME result in the formation of the nonluminescent complexes Ln(mbt F ) 2 (DME) 2 and precipitation of KI in high yields. Single-crystal X-ray diffraction analyses have shown that Eu(mbt F ) 2 (DME) 2 has a trans orientation of mbt F ligands, while in the Yb(mbt F ) 2 (DME) 2 molecule the ligands occupy cis positions. The DFT calculations and estimations with the invariom model revealed that the complexes have a flexible coordination sphere of Ln 2+ ions and a relatively low energy of Ln–mbt F binding. The reactions of the same diiodides with the lithium complex Li(mbt F ) are reversible and proceed through the formation of intermediate complexes of unknown structure which have been isolated as noncrystalline solids. The europium product (solid and in DME solution) upon UV excitation exhibited bright luminescence with λ 510 nm. Data from time-resolved photoluminescence (PL) spectroscopy indicated the existence in the intermediate substance of two Eu 2+ emission centers with different coordinating environments. Treatment of the solid intermediate product with toluene led to its dissociation onto Ln(mbt F ) 2 (DME) 2 and [LiI(DME)] n . The back-replacement of toluene with DME gives again the solutions from which the starting LnI 2 and Li(mbt F )(DME) were precipitated by slow evaporation of the solvent. The reversibility of the processes has been confirmed by the reaction of nonluminescent Eu(mbt F ) 2 (DME) 2 with LiI in DME medium, which resulted in the same luminescent solution which gave a mixture of EuI 2 (DME) 3 and Li(mbt F ).