Synthesis, characterization, crystal structures and thermochemical properties of five lanthanide complexes with mononuclear and binuclear structures

Abstract

Five new lanthanide complexes were synthesized by two different experimental methods: two mononuclear complexes and three binuclear complexes. Their chemical formula is: [Gd(2-Cl-4-FBA)3(terpy)H2O]1.5H2O(1); [Dy(2-Cl-4-FBA)3(terpy)H2O]·0.5H2O(2)) (2-Cl-4-FBA = 2-chloro- 4-fluorobenzoate,terpy = 2,2′:6′,2″-terpyridine); [Ln(3,4-DFBA)3(5,5′-DM-2,2′-bipy)(H2O)]2(Ln = Pr(3),Er(4);[Ln(3,4-DFBA)3(5,5′-DM-2,2′-bipy)]2(Ln = Ho(5)) (3,4-DFBA = 3, 4-difluorobenzoate,5,5′-DM-2,2′-bipy = 5,5′-dimethyl-2,2′-bipyridine). A series of characterization and properties of the complexes were studied, such as elemental analysis, single crystal X-ray diffraction, thermogravimetric analysis, fluorescence properties and so on. The coordination number of complexes 1–2 is 9, showing a muffin geometry. The results show that complex 1–5 crystallized in the triclinic system and space group Pī. Complexes 1 and 2 are isostructural except for the number of free water molecules. Complexes 3–5 are binuclear molecules with different structures. Although the structures of the five complexes are different, they all form one and two-dimensional supramolecular structures along a chain and a plane. The thermal decomposition mechanism of complexes 1–5 was studied by synchronous thermal analyzer infrared spectroscopy (TG/DSC-FTIR). The results show that the coordination water, neutral ligand and acidic ligand are lost in turn when the complex undergoes thermal decomposition. And the three-dimensional infrared images of gas escaping during the thermogravimetric process were analyzed. In addition, the solid state fluorescence spectra of complex 2 was measured and the results showed that the characteristic fluorescence of Dy(III) ion was emitted.