Four dinuclear lanthanide complexes [Ln₂(2-Br-5-MOBA)₆(phen)₂] (Ln = Nd(1), Sm(2), Ho(3), Er(4)) are discussed.

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 Ln³⁺ 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 Ln³⁺ 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.

Four novel lanthanide complexes, [Ln(2,4-DClBA)₃(terpy)(H₂O)]·H₂O (Ln = Eu(1), Tb(2)); [Ln(2,4-DClBA)₃(5,5′-DM-2,2′-bipy)(C₂H₅OH)]₂ (Ln = Eu(3), Tb(4); 2,4-DClBA: 2,4-dichlorobenzoate; terpy: 2,2′:6′,2′′-terpyridine; 5,5′-DM-2,2′-bipy: 5,5′-dimethyl-2,2′-bipyridine) have been synthesized via a conventional solution method at room temperature and structurally characterized by single crystal and powder X-ray diffraction. Complexes 1–2 exhibit mononuclear lanthanide architectures and each Ln³⁺ ion is nine-coordinated adopting a distorted monocapped square antiprismatic molecular geometry, while complexes 3–4 exhibit binuclear lanthanide architectures in which each Ln³⁺ ion is eight-coordinated adopting a distorted square antiprismatic molecular geometry. Mononuclear complexes 1–2 are stitched together via Cl–π and hydrogen bonding interactions to form the 1D, 2D, 3D supramolecular structures. While complexes 3–4 are packed together through Cl–Cl, π–π, and hydrogen bonding interactions to form 1D, 2D supramolecular structures. Luminescence investigation reveals that complexes 1, 3 and 2, 4 display strong red and green emission respectively, showing that terpy and 5,5′-DM-2,2′-bipy can act as sensitizing chromophores, but the former is more effective. The IR, TG-DTG, and the heat capacities of complexes 1–4 were also measured.

In the temperature range of 280 to 350 K, there is a solid-to-solid phase transition for each complex, which is further evidenced by four thermal circulating processes with the scanning rate of 10 K min⁻¹.