Two mono- and dinuclear Eu(iii) enantiomeric pairs based on chiral bis-bidentate bridging ligands: synthesis, structures, luminescent and ferroelectric properties

Using the enantiomeric bis-bidentate bridging ligands (+)/(-)-2,5-bis(4,5-pinene-2-pyridyl)pyrazine (L(S)/L(R)) and depending on the ratio control of reactants, two mono- and dinuclear Eu(iii)-based enantiomeric pairs with the formulae Eu(dbm)(3)L(R/S)·2H(2)O (L(R) in R-1, L(S) in S-1 and dbm = dibenzoylmethanato) and Eu(2)(dbm)(6)L(R/S)·H(2)O (L(R) in R-2 and L(S) in S-2) have been stereoselectively synthesized and structurally characterized. The circular dichroic (CD) spectra confirmed their chiroptical activities and enantiomeric natures. The homochiral dinuclear species represents the first example of a polynuclear lanthanide β-diketonate complexes with circular dichroic and crystallographic evidences. The photoluminescent properties studies revealed that both mono- and dinuclear Eu(iii) complexes exhibited the characteristic red emissions of Eu(iii) ions in the solid state (at 77 K and 300 K) and CH(2)Cl(2) solution. Notably, the photophysical properties of the mononuclear enantiomers were superior to the dinuclear species. Interestingly, R-2 displayed a ferroelectric property at room temperature, which was not observed for R-1 due to the lack of crystalline polarity. R/S-2 are the first examples of homochiral polynuclear lanthanide complexes with luminescence and ferroelectric properties, being potential multifunctional materials.