Dinuclear Tb and Dy complexes supported by hybrid Schiff-base/calixarene ligands: synthesis, structures and magnetic properties

摘要

The synthesis of the new lanthanide complexes [HNEt3][Dy-2(HL1)(L-1)] (5), and [Ln(2)(L-2)(2)] (Ln = Tb-III(7), Dy-III(8)) supported by the hybrid Schiff-base/calix[4]arene ligands H4L1(25-[2-((2-methylphenol)imino)ethoxy]-26,27,28-trihydroxy-calix[4]arene) and H3L2(25-[2-((2-methylpyridine)imino)ethoxy]-26,27,28-trihydroxy-calix[4]arene) are reported. Spectroscopic data (for5) and X-ray crystallographic analysis (for7 center dot 4MeCN,8 center dot 4MeCN) reveal the presence of dimeric structures, featuring doubly-bridged NO(4)Ln(mu-O)(2)LnO(4)N (5) or N(2)O(3)Ln(mu-O)(2)LnO(3)N(2)cores (7,8) with seven-coordinated Ln(3+)ions. The magnetic properties of polycrystalline samples of5,7and8were studied by variable temperature dc and ac magnetic susceptibility measurements. The chi ''(T)vs. Tplots show no maxima in zero field, but the maxima can be detected under a 3 kOe dc field. The relaxation times tau obey the Arrhenius law above 5 K. Anisotropy barriers of similar to 18 cm(-1) (26 K) for 5 and similar to 23 cm(-1)(33 K) for 8 were determined.