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• 作者：Carl-Georg Freiherr von Richthofen ; Anja Stammler ; Hartmut Bgge ; Marty W. DeGroot ; Jeffrey R. Long ; Thorsten Glaser
• 刊名：Inorganic Chemistry
• 出版年：2009
• 出版时间：November 2, 2009
• 年：2009
• 卷：48
• 期：21
• 页码：10165-10176
• 全文大小：1062K
• 年卷期：v.48,no.21(November 2, 2009)
• ISSN：1520-510X

文摘

The reaction of the tris(tetradentate) triplesalen ligand H₆talen^t-Bu₂, which provides three salen-like coordination environments bridged in a meta-phenylene arrangement by a phloroglucinol backbone, with Mn^II salts under aerobic conditions, affords, in situ, the trinuclear Mn^III triplesalen complex [(talen^t-Bu₂){Mn^III(solv)_n}₃]³⁺. This species then reacts with [(Me₃tacn)Cr(CN)₃] to form the tetranuclear complex [{(talen^t-Bu₂)Mn^III₃}{(Me₃tacn)Cr(CN)₃}]³⁺ ([Mn^III₃Cr^III]³⁺). The regular ligand folding observed in the trinuclear triplesalen complex preorganizes the three metal ions for the reaction with three facially coordinated nitrogen atoms of [(Me₃tacn)Cr(CN)₃]. [{(talen^t-Bu₂)(Mn^III(MeOH))₃}{(Me₃tacn)Cr(CN)₃}](ClO₄)₃ (1) was characterized by infrared spectroscopy, elemental analysis, mass spectrometry, electron absorption spectroscopy, and magnetic measurements. The molecular structure was established for the acetate-substituted derivative [{(talen^t-Bu₂)(Mn^III(MeOH))₂(Mn^III(OAc))}{(Me₃tacn)Cr(CN)₃}](ClO₄)₂ (2) by single-crystal X-ray diffraction. Variable-temperature−variable-field and μ_eff versus T magnetic data have been analyzed in detail by full-matrix diagonalization of the appropriate spin-Hamiltonian, consisting of isotropic exchange, zero-field splitting, and Zeeman interaction components. Satisfactory reproduction of the experimental data has been obtained for the parameters J_Mn−Cr = −0.12 ± 0.04 cm⁻¹, J_Mn−Mn = −0.70 ± 0.03 cm⁻¹, and D_Mn = −3.0 ± 0.4 cm⁻¹. These generate a triply degenerate pseudo S_t = 7/2 spin manifold, which cannot be appropriately described by a giant spin model and which exhibits a weak easy-axis magnetic anisotropy. This is corroborated by the onset of a frequency-dependent χ′′ signal at low temperatures, demonstrating a slow relaxation of the magnetization indicative of 1 being a single-molecule magnet. Comparing the properties to those of the heptanuclear analogue [{(talen^t-Bu₂)Mn^III₃}₂{Cr^III(CN)₆}]³⁺ ([Mn^III₆Cr^III]³⁺) formed by the reaction of 2 equiv of [(talen^t-Bu₂){Mn^III(solv)_n}₃]³⁺ with 1 equiv of [Cr(CN)₆]³⁻ [Glaser, T.; Heidemeier, M.; Weyhermller, T.; Hoffmann, R.-D.; Rupp, H.; Mller, P. Angew. Chem. Int. Ed., 2006, 45, 6033−6037] demonstrates a lower driving force for formation, a strongly reduced J_Mn−Cr exchange, a slightly reduced J_Mn−Mn exchange, and a significantly longer Mn−N^N≡C bond length in [Mn^III₃Cr^III]³⁺. Taking into account magneto-structural correlations establishes a supramolecular interaction between the two [(talen^t-Bu₂)Mn^III₃]³⁺ subunits in [Mn^III₆Cr^III]³⁺ responsible for the structural distortion and the short Mn−N^N≡C distance which results in a strong J_Mn−Cr exchange and thus [Mn^III₆Cr^III]³⁺ being a single-molecule magnet with a relatively high effective anisotropy barrier of 25.4 K.