Synthesis, structure, luminescence, and magnetic properties of a single-ion magnet " mer "-[tris(N-(imidazol-4-yl)-methylidene]-dl- phenylalaninato)terbium(III) and related " fac "-Dl-alaninato derivative

Suguru Yamauchi, Takeshi Fujinami, Naohide Matsumoto, Naotaka Mochida, Takayuki Ishida, Yukinari Sunatsuki, Masayuki Watanabe, Masanobu Tsuchimoto, Cecilia Coletti, Nazzareno Re

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Abstract

Two TbIII complexes with the same N6O3 donor atoms but different coordination geometries, "fac"-[Tb III(HLdl-ala)3]·7H2O (1) and "mer"-[TbIII(HLdl-phe)3] ·7H2O (2), were synthesized, where H2L dl-ala and H2Ldl-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 "fac"-[Tb III(HLd-ala)3] and "fac"-[Tb III(HLl-ala)3], while 2 consists of "mer"-[TbIII(HLd-phe)2(HL l-phe)] and "mer"-[TbIII(HLd-phe) (HLl-phe)2]. Magnetic data were analyzed by a spin Hamiltonian including the crystal field effect on the TbIII ion (4f8, J = 6, S = 3, L = 3, gJ = 3/2, 7F 6). 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 φ = 0.50 and 0.61 for 1 and 2, respectively, were observed, and the luminescence fine structure due to the 5D47F6 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 TbIII ion, giving a rationale to the different magnetic anisotropies of 1 and 2.

Original languageEnglish
Pages (from-to)5961-5971
Number of pages11
JournalInorganic Chemistry
Volume53
Issue number12
DOIs
Publication statusPublished - Jun 16 2014

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry

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