Design, Synthesis Of The Oxamido-Bridged Single Molecular Magnets (SMM) Complexes

With the development of the synthesis and researches in functional complexes, the researches in molecular materials with magnetic properties have developed rapidly. Polynuclear complexes have many special structure and magnetism, which offers a new way to design and synthesize molecular magnets. In the complexes, one or more diamagnetic atoms are spaced between two paramagnetic metal ions. So, it is depended on a good bridging ligand and coordination environment to improve Tc. Oxalamide is an excellent bridging group to transmit electronic effect between magnetic centers.In view of above reasons and the stand point of molecular design, we have designed and synthesized new symmetrical ligands and complexes. These compounds were characterized by elernental analysis, IR spectrum, NMR, melting point mensura- tion and single-crystal structur analysis. The main contents are described as following:At chapter 1, the molecular-magnetic complexes and the properties of bridging oxalamide ligand have been summarized.At chapter 2, the new oxalamide bridging ligands N, N'-bis (2-hydroxy-3-methoxy -benzy1) oxalamide (H4L) and N, N'-bis (4-hydroxy-3-methoxy-benzy1) oxalamide (H4LB) were designed and synthesized. The ligand H4L includes an inner N2O2 coordination site with two amides and two phenol functions, an outer O2O2 coordination site involving again the two phenol functions and two oxygen atoms of the methoxy groups, and two amido oxygen atoms positioned out of these two sites. The complexes were characterized by elemental analysis, IR spectrum, NMR, melting point mensuration and crystal structure analysis. The structure analysis indicates that the reverse symmetry ligand H4L molecules are linked into a 2D supermolecular network parallel to (100) by two types of hydrogen bonds. One type occurs between the oxalamide oxygen group and the phenol hydroxyl qroup of the nearest molecule with d(O-H'"O) = 2.832(2) A and∠O-H'"O=121.7°. The other type is between the oxalamide nitrogen group and the phenol hydroxyl group of anther molecule with d(N-H.--O) = 3.006(2) A,∠N-H'"O=164.5°.At chapter 3, rare earth complexes Ln (acac)3·3H2O (Ln=Pr,Nd,Gd,Er,Ho) were synthesized by the reaction of Ln (NO3)3 with Hacac (1:3 mole ratio) in methanol. The complexes were characterized by elemental analysis, IR spectrum and thermal analysis. At chapter 4, Homotetranuclear complexes [Cu2L]2·3H2O, [Co2L]2·3H2O, [Zn2L]2"H2O and [Ni2L]2·2H2O were synthesized by the reaction of acetate salts with H4L(2:1 mole ratio) in methanol solution. The complexes were characterized by IR spectra, Uv-spectra and elemental analyses. The mechanismes of thermal decomposition for the complexes were studied by TG-DSC.At chapter 5, the aim complexes [CuLLn(acac)]n were synthesized by the reaction of [Cu2L]2·3H2O, Ln(acac)3·3H2O with H4L(1:2:1 mole ratio) in dimethyl sulphoxide (DMSO) solution. But unexpected blue crystal Cu(acac)2 was separated from the mixture solution. From the experiment facts, we think that the eaction may be as following: 2Er(acac)3 + Cu2L + H4L = 2HLEr + 2Cu(acac)2 + 2Hacac. The reaction process of mixture solution was observed by Uv-Vis spectrum.