Crystal structures, luminescent properties and thermal decomposition kinetics of some binuclear lanthanide complexes with 2,3-dichlorobenzoic acid anion and 2,2′-bipyridine

Abstract

Some binuclear lanthanide complexes with the general formula [Ln(2,3-DClBA)₃bipy]₂ (Ln = Sm(1), Eu(2), Tb(3), Dy(4), and Ho(5); 2,3-DClBA = 2,3-dichlorobenzoate; bipy = 2,2′-bipyridine) were synthesized and characterized by elemental analysis, molar conductance, infrared, ultraviolet, luminescent spectroscopy, thermogravimetry, and different thermogravimetry (TG–DTG) techniques. The single crystals of the complexes have been obtained except the complex 2 and their structures have been determined by single-crystal X-ray diffraction. The four complexes are isostructural and the rare earth ions are all nine coordinated. The two rare earth ions in each complex are linked by two bridging bidentate and two chelating-bridging tridentate carboxylate groups. Under ultraviolet light excitation, the europium and terbium complexes exhibited characteristic red fluorescence of Eu³⁺ ion and green fluorescence of Tb³⁺ ion at room temperature. The non-isothermal kinetics was investigated by using the integral isoconversional non-linear (NL-INT) and the Popescu methods. The mechanism functions of the first decomposition step of the complexes 3–5 were determined. Meanwhile, the thermodynamic parameters (ΔG ^≠ , ΔH ^≠, and ΔS ^≠) at DTG peak temperatures were also calculated.