Preparation, Crystal Structures, Thermal Decomposition Mechanism And Property Of Lanthanide Aromatic Carboxylic Acids

Eighteen novel complexes([Ln(3,4,5-TEOBA)3phen]2(Ln= La(1), Pr(2), Nd(3), Sm(4), Eu(5), Tb(6), Dy(7), Ho(8)); [Ln(3,4-DEOBA)3phen]2(Ln= Nd(9), Sm(10), Eu(11), Tb(12), Dy(13)); [Ln(3,4-DMOBA)3(H2O)2]·H2O·C2H5OH(Ln= Sm(14), Eu(15), Tb(16), Dy(17), Ho(18)); 3,4,5-TEOBA=3,4,5-triethoxybenzoate; 3,4-DEOBA= 3,4-diethoxybenzoate;3,4-DMOBA=3,4-dimethoxybenzoate;phen=1,10-phenanthroline) constructing by the ligands of 3,4,5-triethoxybenzoic, 3,4-diethoxybenzoic, 3,4-dimethoxybenzoic and 1,10-phenanthroline have been synthesized and characterized by elemental analyses, IR spectrum, NMR spectrum, UV spectrum, Powder X-ray diffraction, single crystal X-ray diffraction and TG/DSC-FTIR technology. And the properties of molar conductance, fluorescence spectra, molar heat capacities and antibiosis activity for title complexes have been measured.Crystal structure of complexes [Ln(3,4,5-TEOBA)3phen]2(Ln= La(1), Pr(2), Nd(3), Eu(5), Tb(6), Dy(7), Ho(8)) and [Ln(3,4-DMOBA)3(H2O)2]·H2O·C2H5OH(Ln= Sm(16), Eu(17), Tb(18), Dy(19), Ho(20)) have been measured by single crystal X-ray diffraction. The results show that complexes 1, 2, 3, 5, 6, 7 and 8 are isostructural and each complex has two asymmetric structure units. The center metal is nine coordinated and can be described as a distorted monocapped square antiprism geometry. Complexes 14,15,16,17 and 18 also have the similar structure and the center Ln3+ ion is eight coordinated, yielding a distorted triangular dodecahedral geometry. Adjacent lanthanide ions are connected by 3,4-DMOBA ligands adopting bridging bidentate mode to generate one-dimensional(1-D) structure.The thermal decomposition mechanism of title complexes has been studied by TG/DSC-FTIR technology. The TG analysis show complexes 1-13 are thermally stable. IR spectra of the evolved gases show 1,10-phen release firstly in the form of gaseous aromatic macromolecules. And then aromatic carboxylic ligands is decomposed into H2 O, CO2 and other gaseous molecules as well as the gaseous organic fragments.The molar heat capacities of complexes 1-13 have been measured by differential scanning calorimetric(DSC). The values of experimental heat capacities are fitted to the polynomial equations by means of least square method in the reduced temperature(x), furthermore, the smoothed heat capacities and thermodynamic functions of complexes are calculated. In addition, there is the solid to solid phase transition on the heat capacities curve for complexes 1, 2, 5, 9, 10, 11 and 12, and it is proved by thermal circulating processes. The phase transition of heating processes for complex 1 has been investigated by the iso-conversional method: M. J. Starink and modified Madhusudanan-Krishnan-Ninan. The result shows that the activation energy(E) and the percent conversion(α) exhibit the fine linear relationship.Biological activity of complexes 9-13 have been measured by means of agar-diffusion method against Escherichia coli, Staphylococcus aureus, and Candida albicans. All complexes have good antibiosis properties, and the antibiosis property against fungus for complexes is higher than bacteria.