Crystal structures, luminescent and thermal properties of a new series of lanthanide complexes with 4-ethylbenzoic acid

A series of lanthanide complexes with the 4-ethylbenzoic acid ligand (4-eba), [Ln(4-eba)(3)(phen)](2) (Ln = Nd (1), Sm (2), Eu (3), Tb (4), Dy (5) and Ho (6); phen = 1,10-phenanthroline), have been synthesized and structurally characterized by single-crystal X-ray diffraction. In the isostructural complexes 1-4, two Ln(3+) ions are connected together by four bridging 4-eba ligands, with two of them in a bidentate-bridging mode and the other two in a bidentate chelating-bridging mode, and each Ln(3+) is also chelated by one 4-eba group and one phen ligand, giving a coordination number of nine. In complex 5, however, two eight-coordinated Dy3+ ions are held together only by two bidentate-bridging 4-eba ligands, and another two 4-eba ligands coordinate to one Dy3+ ion in a chelating mode. In complex 6, each Ho3+ ion is eight-coordinated to four bidentate-bridging 4-eba ligands, one chelating 4-eba group and one chelating phen ligand. Thermal analysis of the six complexes is discussed by TG-DTG and IR techniques. The activation energy E values of the first decomposition stage for complexes 1-6 are calculated by integral isoconversional non-linear (NL-INT) and Ozawa iteration methods, respectively. The fluorescent properties of complexes 3 and 4 are also studied.