Synthesis, crystalline structure and photoluminescence investigations of the new trivalent rare earth complexes (Sm3+, Eu3+ and Tb3+) containing 2-thiophenecarboxylate as sensitizer

New complexes with the general formula [RE(TPC)3 · (H2O)2], where RE=Eu3+, Sm3+, Gd3+, Tb3+ and TPC=2-thiophenecarboxylate, have been prepared and investigated by photoluminescence spectroscopy. These compounds were characterized by complexometric titration, elemental analyses and infrared spectroscopy. The X-ray crystal structure has been determined for the [Eu(TPC)3 · (H2O)2] compound, indicating that this complex is in dimeric form bridged by two carboxylate ions with monoclinic crystal system and space group P21/n. The coordination polyhedron can be described as a distorted square antiprism, where six oxygen atoms belong to the TPC ligand and two oxygen atoms belong to the water molecules, with site symmetry close to C2v. The theoretical value of the intensity parameter , which is in agreement with the experimental one, indicates that the Eu3+ ion is in a highly polarizable chemical environment. Based on the luminescence spectra, the energy transfer from the ligand triplet state (T) of TPC to the excited levels of the Eu3+ ion is discussed. The emission quantum efficiency of the 5D0 emitting level of the Eu3+ ion was also determined. In the case of the Tb3+ ion, the photoluminescence data show the high emission intensity of the characteristic transitions 5D4 → 7FJ (J=0–6), indicating that the TPC ligand is a good sensitizer. It is also noticed that the complexes with the Eu3+ and Tb3+ ions are more luminescent than the complex with the Sm3+ ion.