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 P2(1)/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 C-2v. The theoretical value of the intensity parameter Omega(2), 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 D-5(0) 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 D-5(4) --> F-7(J) (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. (C) 2003 Elsevier B.V. All rights reserved.