Synthesis, Structure, Luminescence, and Magnetic Properties of a Single-Ion Magnet 鈥?i>mer鈥?[Tris(N-[(imidazol-4-yl)-methylidene]-dl-phenylalaninato)terbium(I

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• 作者：Suguru Yamauchi ; Takeshi Fujinami ; Naohide Matsumoto ; Naotaka Mochida ; Takayuki Ishida ; Yukinari Sunatsuki ; Masayuki Watanabe ; Masanobu Tsuchimoto ; Cecilia Coletti ; Nazzareno Re
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：June 16, 2014
• 年：2014
• 卷：53
• 期：12
• 页码：5961-5971
• 全文大小：527K
• 年卷期：v.53,no.12(June 16, 2014)
• ISSN：1520-510X

文摘

Two Tb^III complexes with the same N₆O₃ donor atoms but different coordination geometries, 鈥?i>fac鈥?[Tb^III(HL^dl-ala)₃]路7H₂O (1) and 鈥?i>mer鈥?[Tb^III(HL^dl-phe)₃]路7H₂O (2), were synthesized, where H₂L^dl-ala and H₂L^dl-phe are N-[(imidazol-4-yl)methylidene]-dl-alanine and -dl-phenylalanine, respectively. Each Tb^III ion is coordinated by three electronically mononegative NNO tridentate ligands to form a coordination geometry of a tricapped trigonal prism. Compound 1 consists of enantiomers 鈥?i>fac鈥?[Tb^III(HL^d-ala)₃] and 鈥?i>fac鈥?[Tb^III(HL^l-ala)₃], while 2 consists of 鈥?i>mer鈥?[Tb^III(HL^d-phe)₂(HL^l-phe)] and 鈥?i>mer鈥?[Tb^III(HL^d-phe)(HL^l-phe)₂]. Magnetic data were analyzed by a spin Hamiltonian including the crystal field effect on the Tb^III ion (4f⁸, J = 6, S = 3, L = 3, g_J = 3/2, ⁷F₆). The Stark splitting of the ground state ⁷F₆ was evaluated from magnetic analysis, and the energy diagram pattern indicated easy-plane and easy-axis (Ising type) magnetic anisotropies for 1 and 2, respectively. Highly efficient luminescences with 桅 = 0.50 and 0.61 for 1 and 2, respectively, were observed, and the luminescence fine structure due to the ⁵D₄ 鈫?⁷F₆ transition is in good accordance with the energy diagram determined from magnetic analysis. The energy diagram of 1 shows an approximate single-well potential curve, whereas that of 2 shows a double- or quadruple-well potential within the ⁷F₆ multiplets. Complex 2 displayed an onset of the out-of-phase signal in alternating current (ac) susceptibility at a direct current bias field of 1000 Oe on cooling down to 1.9 K. A slight frequency dependence was recorded around 2 K. On the other hand, 1 did not show any meaningful out-of-phase ac susceptibility. Pulsed-field magnetizations of 1 and 2 were measured below 1.6 K, and only 2 exhibited magnetic hysteresis. This finding agrees well with the energy diagram pattern from crystal field calculation on 1 and 2. DFT calculation allowed us to estimate the negative charge distribution around the Tb^III ion, giving a rationale to the different magnetic anisotropies of 1 and 2.