First crystal structures of lanthanide-hydrocinnamate complexes: Hydrothermal synthesis and photophysical studies

Five new lanthanide(III) complexes of hydrocinnamic acid (Hcin), [Ln(cin)3(H2O)3]·3Hcin (Ln = Tb(III) (1), Dy(III) (2), Er(III) (3), Eu(III) (4) and Gd(III) (5)) have been synthesized and characterized. The X-ray structures of 1–5 reveal that all compounds are isostructural and that each lanthanide ion is nine – coordinated by oxygen atoms in an overall distorted tricapped trigonal-prismatic geometry. Six oxygen atoms are provided by carboxylate moieties, and the other three by water molecules. The supramolecular architectures of 1–5 show the presence of uncoordinated hydrocinnamic acid molecules which induce the formation of numerous hydrogen bonds. The photophysical properties of these complexes in the solid state at room temperature were studied using diffuse reflectance (DR), fluorescence excitation and emission spectra. An energy level diagram was used to establish the most relevant channels involved in the ligand-to-metal energy transfer, indicating that cin− ligands can act as intramolecular energy donors for Tb(III), Dy(III) and Eu(III) ions.

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► First Ln3+-hydrocinnamate complexes have been synthesized and characterized.
► Supramolecular architectures are induced by the formation of hydrogen bonds.
► Tb3+, Dy3+ and Eu3+ complexes photoluminescence properties were investigated.
► An energy level diagram is used to establish the ligand-to-metal energy transfer.
► η low value of approximately 11% reflects the large value of non-radiative rate.