Studies On Construction And Magneto-structural Relationship Of Single-ion Magnets Based On Kramers Ions Dy(Ⅲ),Er(Ⅲ) And Co(Ⅱ)

Single molecule magnets have wide application prospects in molecular spintronics,quantum mechanics,high-density information storage materials and other fields.Since Ishikawa et al.reported the first single ion magnet（SIM）based on lanthanide metal in 2003,SIMs have become a hot topic in recent years because of their simple structures and high energy barrier inversion.Due to the non-quenched orbital angular momentum of lanthanide metal ions,the mononuclear complexes based on lanthanide metals have very large magnetic anisotropy,resulting in slow magnetic relaxation.In recent years,SIMs based on lanthanide metal have made great progress.The highest energy barrier 1837 K and the blocking temperature 60 K were observed in Dy（Ⅲ）-based SIM.Transition metal ions also have orbital angular momentum,which has attracted the attention of researchers.In 2010,the Long group reported the first high spin Fe（Ⅱ）-based SIM,which is also the first case of single ion magnets based on transition metal.Subsequently,the studies for single ion magnets based on transition metal developed rapidly.Cobalt（Ⅱ）is superstars for SIMs based on transition metals In this paper,the synthesis and magnetic relations of the single ion magnets Kramers ion based on Dy（Ⅲ）,Er（Ⅲ）and Co（Ⅱ）are mainly studied,including the following three parts:1.Slow magnetic relaxation in luminescent mononuclear dysprosium（Ⅲ）and erbium（Ⅲ）pentanitrate complexes with the same LnO₁₀ coordination geometry.Two isostructural mononuclear Dy and Er pentanitrate complexes（nBu₄N）₂[Dy（NO₃）₅]（1）and（nBu₄N）₂[Er（NO₃）₅]（2）with a LnO₁₀ coordination geometry have been synthesized and studied by single-crystal X-ray diffraction,luminescence and magnetic measurements.Slow relaxation of the magnetization behavior is simultaneously observed in two complexes with the same coordination environment,despite the different types of the 4f-shell electron distribution.Meanwhile,both complexes exhibit the respective characteristic Ln（Ⅲ）photoluminescence.2.Slow magnetic relaxation influenced by symmetry change from ideal C_i to D_3dd in cobalt（Ⅱ）-based single-ion magnets.The coordination geometries of the Co（Ⅱ）site in two complexes[Co（imidazole）₆][BPh₄]₂·0.3CH₃CN（3）and[Co（imidazole）₆][NO₃]₂（4）display the ideal symmetries C_i and D_3d,respectively.Both complexes are field-induced single-ion magnets.The effective energy barrier exhibits a reduced tendency with the local symmetry changing from low-symmetry Ci to high-symmetry D3d..3.Slow magnetic Relaxation in an octahedral cobalt（Ⅱ）complexes with positive axial Anisotropy.A mononuclear Co（Ⅱ）complexes[Co（L）4（NO3）2]（L=3-phenylpyrazole）（5）featuring distorted octahedral geometry was prepared and structurally characterized by X-ray crystallographic analyses.Direct-current magnetic and high-frequency field electron paramagnetic resonance measurements reveal that the complex has the large and positive D value with the non-negligible transverse anisotropy（E）.Slow magnetic relaxation was observed under the applied direct-current field by dynamic alternative-current magnetic susceptibility measurements,which provide an interesting examples for six-coordinate Co（Ⅱ）-based single ion magnets constructed by nitrate groups and nitrogen heterocyclic compounds in mono-dentate coordination modes.