A new family of trinuclear Nickel(II) complexes as single-molecule magnets

Rituparna Biswas, Yumi Ida, Michael L. Baker, Saptarshi Biswas, Paramita Kar, Hiroyuki Nojiri, Takayuki Ishida, Ashutosh Ghosh

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38 Citations (Scopus)

Abstract

Three new trinuclear nickel (II) complexes with the general composition [Ni3L3(OH)(X)](ClO4) have been prepared in which X=Cl- (1), OCN- (2), or N3- (3) and HL is the tridentate N,N,O donor Schiff base ligand 2-[(3- dimethylaminopropylimino)methyl]phenol. Single-crystal structural analyses revealed that all three complexes have a similar Ni3 core motif with three different types of bridging, namely phenoxido (μ2 and μ3), hydroxido (μ3), and μ2-Cl (1), μ1,1-NCO (2), or μ1,1-N3 (3). The nickel(II) ions adopt a compressed octahedron geometry. Single-crystal magnetization measurements on complex 1 revealed that the pseudo-three-fold axis of Ni3 corresponds to a magnetic easy axis, being consistent with the magnetic anisotropy expected from the coordination structure of each nickel ion. Temperature-dependent magnetic measurements indicated ferromagnetic coupling leading to an S=3 ground state with 2J/k=17, 17, and 28 K for 1, 2, and 3, respectively, with the nickel atoms in an approximate equilateral triangle. The high-frequency EPR spectra in combination with spin Hamiltonian simulations that include zero-field splitting parameters DNi/k=-5, -4, and -4 K for 1, 2, and 3, respectively, reproduced the EPR spectra well after a anisotropic exchange term was introduced. Anisotropic exchange was identified as Di,j/k=-0.9, -0.8, and -0.8 K for 1, 2, and 3, respectively, whereas no evidence of single-ion rhombic anisotropy was observed spectroscopically. Slow relaxation of the magnetization at low temperatures is evident from the frequency-dependence of the out-of-phase ac susceptibilities. Pulsed-field magnetization recorded at 0.5 K shows clear steps in the hysteresis loop at 0.5-1 T, which has been assigned to quantum tunneling, and is characteristic of single-molecule magnets. Nickel(II) magnets: A new family of trinuclear Ni II complexes with phenoxido (μ2 and μ3), hydroxido (μ3), and μ2-Cl, μ1,1-NCO, or μ1,1-N3 bridges have been prepared that form face-sharing coordination polyhedra (see figure). The three complexes exhibit a dominant ferromagnetic exchange coupling with sizable uniaxial anisotropy. The slow magnetization relaxation, the hysteresis of the pulsed-field magnetization, a magnetic easy axis, and the high-frequency EPR spectra show that these complexes constitute a new class of single-molecule magnets.

Original languageEnglish
Pages (from-to)3943-3953
Number of pages11
JournalChemistry - A European Journal
Volume19
Issue number12
DOIs
Publication statusPublished - 2013 Mar 18

Keywords

  • EPR spectroscopy
  • Schiff bases
  • X-ray diffraction
  • magnetic properties
  • nickel

ASJC Scopus subject areas

  • Catalysis
  • Organic Chemistry

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