Organic magnetism is a rapidly developing field that combines the skills of experimental and theoretical scientists in many areas of chemistry and physics.Compared with inorganic ferromagnet,the organic ferromagnet exhibits the characteristics of structural diversities,low density,and readily processing.In addition,layer-by-layer (LBL) assembled multilayered films have received considerable interest because they allow fabrication of supramolecules with tailored architecture and properties.The design and preparation of organic soft ferromagnets by self-assembling is reported in this article.4,4′-(4,4′-Bithiazole-2,2′-diylbis(diazene-2,1-diyl))diphenol (BTDP) was first synthesized from phenol and 2,2′-diamino-4,4′-bithiazole (DABT),and the structure of BTDP was characterized by ~1H-NMR.The hydroxyls of the BTDP provide anions while the poly(diallydimethylammonium chloride) (PDDA) provides cations,so the layer-by-layer self-assembling of BTDP with PDDA was carried out based on the electrostatic interaction on the polyethylene (PE) surface with carboxylic acid groups (—COOH).BTDP coordinates with transition metal ions since two nitrogen atoms in the thiazole rings and metal ions can provide stable five-member rings.Therefore,the complexes of assembled multilayer films (PE-(PDDA/BTDP-M~ 2+ )_n) were also prepared via layer-by-layer assembly.The assembling process was monitored by UV-Vis spectroscopy.The linear increase of the absorbance at 413 nm with increasing the layer number indicates a process of uniform assembling.The structure of the complexes was characterized by FTIR,which suggests that the chelation has taken place demonstrated by the shift of the characteristic absorption band.In addition,the BTDP and PDDA deposition obtained by mixing their solutions could react with transition metal ions to form their metal complexes,which was also characterized by FTIR.The magnetic properties of these complexes were measured using a Physical Property Measurement System (PPMS-9),which included magnetization versus temperature,magnetization versus applied field,magnetic susceptibility versus temperature and magnetic hysteresis.The temperature is ranged from 4 to 300 K, and the intensity of magnetic field is in the range of -4×10~6～4×10~6 A/m.It was found that these complexes were organic soft magnets and had typical "S" shaped magnetic hysteresis loops.The saturation magnetization of the complex of assembled multilayer film PE-(PDDA/BTDP-Ni~ 2+ )_ 25 is 5.30 emu/g, and the paramagnetic Curie temperature is 128 K,while the remanence magnetization and coercivity are 0.0049 emu/g and 2228.17 A/m,respectively.The results show that PE-(PDDA/BTDP-Ni~ 2+ )_ 25 is an organic soft ferromagnet at low temperatures.The magnetic properties of the multilayer film for PE-(PDDA/BTDP-Cu~ 2+ )_ 25 is similar with those for PE-(PDDA/BTDP-Ni~ 2+ )_ 25 .The saturation magnetization of deposit complex PDDA/BTDP-Cu~ 2+ is 2.60 emu/g, and the paramagnetic Curie temperature is -10 K,while the remanence magnetization and coercivity are 0.0035 emu/g and 2307.75 A/m, respectively.The results show that PE-(PDDA/BTDP-Cu~ 2+ )_ 25 is an organic soft antiferromagnet at low temperatures.The magnetic properties of deposition for PDDA/BTDP-Cu~ 2+ are similar with those for PDDA/BTDP-Ni~ 2+ .In comparison,it was proved that the magnetic properties of multilayer self-assembled films were much better than those of deposited complexes.The strong ferromagnetism of the multilayered film may arise from the exchange interaction of the transition metal ions in the ligands which show a well-ordered 3-D network structure.
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Jul 18, 2017
Dangwei Guo + 1
Open Access