Modulation of the directions of the anisotropic axes of DyIII ions through utilizing two kinds of organic ligands or replacing DyIII ions by FeIII ions

Abstract

To modulate the molecular symmetry of tetrahedral Dy₄ complexes, in this paper, we reported two complexes based on a Dy₄ or Dy₂Fe₂ tetrahedral unit, namely, [Dy₄(NO₃)(HL)₄{(py)₂C(OH)O}₂](OH)·6CH₃CN·0.5H₂O (1, H₃L = 2-((2-hydroxybenzylidene)amino) propane-1,3-diol, (py)₂C(OH)₂ = the gem-diol form of di-2-pyridyl ketone) and [Fe₄Dy₂(μ₄-O)(HL)₃{(py)₂CO₂}{(py)₂C(OH)O}{(py)₂C(OCH₃)O}(L′)Cl₃]Cl·6CH₃CN·3.5H₂O (2, H₂L′ = 2-amino-1,3-propanediol). In 1, each of the four sides of the Dy₄ tetrahedron was constructed from one O atom of one (py)₂C(OH)O⁻ ligand and one O atom of one HL₁²⁻ ligand, one side was constructed from two O atoms of two (py)₂C(OH)O⁻ ligands, and the remaining side was not constructed from organic ligands. Consequently, NO₃⁻ in 1 adopts an unprecedented η⁴, η¹, η¹, μ₄ coordination mode, in which one O atom (O17) linked with four Dy^III and each of another two O atoms further coordinated with a Dy^III ion. For 2, the tetrahedral unit was composed of two Dy^III ions and two Fe^III ions, and each of the two Dy^III ions is further linked with an Fe^III ion. Slow relaxation behavior was observed for both complexes, with an energy barrier of 8.73 K for 1 under a zero dc field and 13.80 K for 2 under a 1500 Oe dc field, respectively. The orientations of the magnetic anisotropy of Dy^III in 1 and 2 were calculated by the Magellan program, indicating that the easy magnetization axes of the four Dy^III ions in 1 were not directed to O17, while the axes in 2 are nearly parallel to each other.