Eu(III) and Tb(III) Complexes with the Nonsteroidal Anti-Inflammatory Drug Carprofen: Synthesis, Crystal Structure, and Photophysical Properties

Two
new lanthanide complexes with general formula [Ln2(carprofen)6­(DMF)2] (Ln = Eu (1), Tb (2), DMF = N,N-dimethylformamide,
carprofen = 6-chloro-α-methylcarbazole-2-acetic
acid) have been synthesized by a hydrothermal method. Complex 1 was characterized by single-crystal X-ray diffraction (XRD),
and it was found to crystallize in the monoclinic space group C2/c. The coordination of the ligand to
the lanthanide ion has been investigated by Fourier-transform infrared
(FTIR) spectra and ultraviolet–visible (UV–vis) absorption
spectra. Complex 1 emits red light, but the antenna effect
of the ligand is not effective, whereas complex 2 presents
intense green emission with effective energy transfer from the ligand.
The different performance of the two complexes is related to the energy
matching between the excited states of the lanthanide ion and the
triplet state of the ligand. The intramolecular energy transfer mechanisms
are also discussed.