Synthesis, crystal structures and magnetic properties of a series of pentanuclear heterometallic [Cu II3Ln III2] (Ln = Ho, Dy, and Gd) complexes containing mixed organic ligands

Abstract

In this paper, we present the synthesis, crystal structures and magnetic properties of three complexes with formulae [Cu₃Ln₂(L)₂(teaH)₂(N₃)₂Cl₂]·xCH₃CN (H₂L = N1,N3-bis(3-methoxysalicylidene)diethylenetriamine, teaH₃ = triethanolamine; Ln = Ho, x = 3 for 1, Ln = Dy, x = 2 for 2 and Ln = Gd, x = 3 for 3), and the structural topologies of 1–3 are unprecedented. The structural analyses revealed that the metal ions in 1–3 formed a kite-like topology with Ln1, Ln2 and Cu1 located on the body, while Cu2 and Cu3 located on both wings. The dc data of 3 were fitted, which showed that the magnetic couplings are antiferromagnetic between Cu^II and between Gd^III ions, while they are ferromagnetic between Cu^II and Gd^III ions. AC magnetic susceptibility studies for 1 and 2 indicated that both complexes exhibit frequency dependent χ′′ signals at low temperature, but no χ′′ peaks were observed, which may be due to the deviation from ideal geometry for Ho^III in 1 and Dy^III in 2 and the presence of weak magnetic couplings between paramagnetic ions within the two complexes. For 3, the ac magnetic susceptibilities with zero dc fields show no frequency dependent χ′′ signals because of the isotropy of Gd^III. The orientation of the easy magnetization axes of two Dy^III in 2 was estimated using the Magellan program, indicating that the magnetic anisotropy axes for Dy1 and Dy2 are almost perpendicular with the angle of 86.630°.