Construction and magnetic study of two new dysprosium complexes with chain or tetranuclear structure

Abstract

Two novel dysprosium complexes, namely, [Dy₂L₂(NO₃)₂(DMF)₂]·2DMF (1) and [Dy₄L₄(OAc)₄(DMF)₂] (2), have been successfully synthesized by reacting a new pyridine-N-oxide-containing organic ligand N′-(8-hydroxyquinoline-2-carboxaldehyde)pyridine-N-oxide-carbohydrazide (H₂L) with different dysprosium salts. The single-crystal X-ray diffraction study revealed that they show either one-dimensional (1D) or tetranuclear structure that is governed by the coordination anion used during the reaction. Within the 1D structure of 1, the nine-coordinated Dy³⁺ ions are bridged by two phenol oxygen atoms from the 8-hydroxyquinoline group to form Dy₂ dimers and these dimers are further connected by pyridine-N-oxide groups. While in 2, the two octa-coordinated Dy³⁺ ions are bonded together by both phenol oxygen and acetate bridges to produce the Dy₂ units and two adjacent Dy₂ units are further linked by pyridine-N-oxide groups, resulting in a tetranuclear structure. Magnetic studies indicate that the anisotropic Dy³⁺ ions in 1 and 2 are ferromagnetically and anti-ferromagnetically coupled, respectively. The alternating current (ac) susceptibility measurements revealed slow magnetic relaxation with effective energy barriers of U_eff = 18.0 K under zero dc field in complex 1. However, under zero dc field, the ac data for 2 show negligible out-of-phase signals, excluding the existence of slow magnetic relaxation. Theoretical studies indicate that the different magnetic relaxation behaviors of both complexes were attributed to the different coordination environments around Dy³⁺ ions and the distinct magnetic coupling between them.