Complexes Based On Aromatic Carboxylic Acids And N-hetercyclic Ligands: Synthesisand Magnetic Property

Taking aromatic carboxylic acids and N-hetercyclic as ligands, nineteen novel complexes were synthesized in this thesis, which were fully characterized by single crystal X-ray diffraction, elemental analysis, powder X-ray diffraction, thermo-gravimetric analysis, circular dichroism(CD) spectrum and so on. The structures and magnetic properties of the complexes were analyzed in detail. The main contributions in this thesis are listed as below:1. Four transition metal(Co and Cu) complexes were synthesized based on aromatic carboxylate acids and N-hetercyclic ligands. The magneto-structural correlations have been studied. Through comparing the two Cu complexes, it is concluded that changing the non-coordinated groups of ligands may affect the coordination modes of the ligands and afford distinguishingly different structures and properties. One of the Co complex with {Co6} clusters was futher linked through the ligands into a three dimentional(3D) framework in bcu topo, which showed a 3D antiferromagnetic ordering at ca. 8 K; the other Co complex was a 2D structure containing Co chains, which exhibited slow magnetic relaxation behavior at low temperatures.2. The employment of 1H-1,2,4-triazole, RE3+(RE = rare earth) and Co2+ ions, has afforded a series of heterometal complexes with the 3-nitrophthalic acid as a template, which were simplified into a rare topology of 4,8T10. Novel {RECo8O10} clusters with a sandglass-like structure were observed in the complex. The isostructural complexes with different RE3+ ions displayed distrinct magnetic properties,such as spin canting, spin glass, spin frustrate,slow magnetic relaxation behavior and magnetic ordering. Additionally, the magnetocaloric effect of the Gd-system has also been explored.3. Based on aromatic carboxylic acids and N-hetercyclic ligands, two series of Ln complexes with 1D chain were obtained. One is a Dy-based complex, which is in a helix chain bridged by nicotinic acid ligand from in situ decarboxylation of pyridine-2,3-dicarboxylic acid. The magnetic studies showed that it displayed ferromagnetic coupling between the Dy3+ and slow magnetic relaxation behaviour under zero direct current(dc) field, which exhibited a rare example of a Dy-based helix chain exhibiting single-molecule magnet(SMM) behaviour. Another series of Ln complexes(Ln = Gd, Tb, Dy, Ho and Er) with 1D zig-zag structure, in which the Ln ions were connected by a pair of water-bridges. Magnetic investigation reveals that the Tb, Dy, Ho, Er-analogue exhibits ferromagnetic interactions and slow magnetic relaxation behavior under zero dc field. The surveys of the magneto-structure and magnetic dilution method were applied to elucidate the coexistence of magnetic ordering and slow magnetic relaxation observed in the alternate current(ac) susceptibility signal of the Dy-complex, in which the complicatied magnetic behavior was proposed to originate from the noncollinear spin arrangement in the zig-zag chain and the slow magnetic relaxation should be mainly attributed to the single ion behavior.