Homochiral mono- and dinuclear SmIII complexes showing the effect of nuclearity on their photophysical properties

Using the enantiopure bis-bidentate ligands (−)/(+)-2,5-bis(4,5-pinene-2-pyridyl)pyrazine (LR/LS), two mono- and dinuclear SmIII enantiomeric pairs with the formulae [Sm(dbm)3LR/S]·C2H6CO·H2O (R-1 and S-1 being the isomers containing the LR and LS ligands, respectively, and dbm = dibenzoylmethanate) and [Sm2(dbm)6LR/S]·2H2O (R-2 and S-2 being the isomers containing the LR and LS ligands, respectively) have been synthesized and characterized by X-ray crystallography and spectroscopic technologies. The nuclearity of the complexes isolated depends on the ratio of the reactants. Circular dichroic (CD) spectra confirmed their chiroptical activities and enantiomeric natures. Measurement of the luminescence properties revealed that both the mono- and dinuclear SmIII complexes display the characteristic deep-red emissions of SmIII ions in the solid state. Notably, in contrast to the previously reported dinuclear SmIII complex based on a bis-β-diketonate ligand, whose emission intensity is much larger than that of the mononuclear analog, the intensity of the emission signal for the mononuclear complex R-1 is more than ten times larger than that of the dinuclear species R-2. The reason for this phenomenon is elucidated in this work. Thus, our research results demonstrate that the Sm nuclearity has a considerable effect on the photophysical properties of SmIII mono-β-diketonate complexes, which is contrary to the observation in SmIII bis-β-diketonate complexes.

Using enantiopure bis-bidentate ligands, two mono- and dinuclear SmIII enantiomeric pairs have been synthesized, depending on the ratio of the reactants. The photophysical properties of the mononuclear SmIII enantiomers are superior to those of the dinuclear SmIII analogs, demonstrating that the Sm nuclearity has a considerable effect on their photophysical properties.Figure optionsDownload as PowerPoint slide