Preparation, Structure, Thermal Chemical Properties Of Lanthanide Complexes With Halogen-Benzoic Acid And 1,10-Phenanthroline

In order to promote the application of the rare earth aromatic carboxylic acid complexes, we have synthesized twenty-three rare earth ternary complexes at room temperature by a solution-precipitation method, in which benzoic acid or halogen-benzoic acid were used as the acid ligand, and 1,10-phenanthroline as the neutral ligand. They are [Ho(BA)₃phen]₂, [Ln(2,3-DClBA)₃phen]₂, [Ln(2-Cl-4-FBA)₃phen]₂ (Ln =Nd, Sm, Eu, Tb, Dy, Ho), [Ln(2,5-DClBA)₃phen]₂, (Ln = Sm, Eu, Tb, Dy, Ho), [Ln(5-Cl-2-MOBA)₃phen]₂ (Ln =Nd, Sm, Eu, Ho) and [Sm (2-Cl-4,5-DFBA)₃(phen)(H₂O)]₂.The metal Ln³⁺ contents in the complexes were assayed using an EDTA titration method and the contents of C, H, and N were determined by element analyzer. The complexes were characterized and studied by molar conductance, infrared, ultraviolet, fluorescence spectroscopy, X-ray powder diffraction, thermal analysis and so on.The structures of six ternary complexes of [Nd(2-Cl-4-FBA)₃phen]₂, [Sm(2,5-DClBA)₃phen]₂, [Tb(2,5-DClBA)₃phen]₂, [Sm(5-Cl-2-MOBA)₃phen]₂, [Sm (2-Cl-4,5-DFBA)₃(phen)(H₂O)]₂ and [Ho(BA)₃phen]₂ have been determined by X-ray single crystal diffraction. The results show that they are all binuclear molecular and crystallize in triclinic, space group pÄ«. Carboxylate groups coordinated to metal Ln³⁺ ions present four kinds of coordination modes: unidentate, chelating bidentate, bridging bidentate and bridging-chelating tridentate. For the complex [Ho(BA)₃phen]₂, the coordination geometry of the center ion Ho³⁺ is eight-coordinated square antiprismatic conformation. The complex [Nd(2-Cl-4-FBA)₃phen]₂ has two types of binuclear molecules in its crystal and the coordination geometries of the corresponding center ion Nd³⁺ is a distorted nine-coordinated monocapped square antiprismatic or a distorted tricapped triangular prism comformation, respectively. For the others four complexes, the center ions are all nine coordination and the coordination geometries are distorted nine-coordinated monocapped square antiprismatic comformations.The thermostability and the thermal decomposition processes of the complexes are discussed by TG-DTG and IR techniques. The integral isoconversional non-linear method, Madhusudanan-Krishnan-Ninan method and Malek method are employed to investigate the kinetics of the second thermal decomposition process of [Ho(BA)₃phen]₂ and the first thermal decomposition process of [Sm(5-Cl-2-MOBA)₃phen]₂. The corresponding kinetic parameters (activation energy E and pre-exponential A) and the thermodynamic parameters (ΔG^≠,ΔH^≠andΔS^≠) are also calculated.The continuous heat capacities of the seven complexes [Ho(BA)₃phen]₂, [Ln(2,3-DClBA)₃phen]₂, [Ln(2-Cl-4-FBA)₃phen]₂ (Ln = Eu, Tb, Ho) were measured by DSC technology using indirect measurement method (specific heat comparison method). In addition, the thermodynamic parameters, enthalpy (H_T-H_{298.15 K}), entropy (S_T-S_{298.15 K}) and Gibbs free energy (G_T-G_{298.15 K}) of the complexes relative to the standard reference temperature 298.15 K were also calculated.The thermal decomposition behaviors and the evolved gases of ten complexes [Ho(BA)₃phen]₂, [Ln(2,5-DClBA)₃phen]₂, (Ln = Sm, Eu, Tb, Dy, Ho), [Ln(5-Cl-2-MOBA)₃phen]₂, (Ln =Nd, Eu, Ho) and [Sm (2-Cl-4,5-DFBA)₃(phen)(H₂O)]₂ have been discussed by simultaneous TG/DSC-FTIR technique. The activation energy E of the decomposition steps for the complexes [Sm(2,5-DClBA)₃phen]₂, [Tb(2,5-DClBA)₃phen]₂ and [Sm (2-Cl-4,5-DFBA)₃(phen)(H₂O)]₂ are calculated by the integral isoconversional non-linear method.