Photoluminescent complexes of Eu(III), Tb(III) and Gd(III) with 3-thiopheneacetate and 4,4′-dimethyl-2,2′-bipyridine: Synthesis, characterization and photophysical properties

Abstract

Three crystals of lanthanide complexes with 3-thiophenoacetic acid (3-HTAA) and 4,4′-dimethyl-2,2′-bipyridine (dmbpy) ligands were synthesized. The structures of the complexes [Ln2(3-TAA)6(dmbpy)2] [Ln = Eu(III), Tb(III), Gd(III)] were determined by single crystal X-ray diffraction, where all crystals are isostructural and belong to the triclinic crystal system with P-1 space group. The complexes were characterized by CHN elemental analysis and spectroscopic techniques in the Infra-red region and Raman scattering. The dimeric structures have different modes of coordination using carboxylic and nitrogen groups present in the ligands. To investigate the photoluminescence properties, the Eu(III) and Gd(III) complexes was selected. The triplet state (23,529 cm−1) was determined by the emission spectrum of the Gd(III) complex. Sparkle/PM3 model was also used to predict the ground state geometries of the Eu(III) complex. The intensity parameters (Ω2, Ω4 and Ω6), energy transfer rates, radiative and non-radiative rates (Arad and Anrad), quantum efficiency (η) and quantum yield (q) were determined by quantum mechanics calculation using the LUMPAC software. Crystal structures, spectroscopic properties and their photoluminescence behavior are discussed.