Designing asymmetric Dy2 single-molecule magnets with two-step relaxation processes by the modification of the coordination environments of Dy(iii) ions

Abstract

The reaction of Dy(NO₃)₃·6H₂O and an asymmetric Schiff-base linker 5-chloro-2-(((2-hydroxy-3-methoxybenzyl)imino)methyl) phenol (H₂L) afforded a dinuclear compound [Dy₂L₂(HL)(NO₃)(EtOH)]·0.5C₂H₅OH (1). Complex 1 features two inequivalent Dy(III) sites, where three ligand sets (one HL⁻ moiety and two L²⁻ groups) are shared by two Dy(III) ions. The strategic introduction of CH₃COOH in the reaction system used for synthesizing 1 induces the replacement of the HL⁻ ligand by the CH₃COO⁻ ion, consequently resulting in the generation of [Et₃NH][Dy₂L₂(NO₃)(CH₃COO)₂] (2). In complex 2, two Dy(III) centers adopt NO₇ (D_2d geometry) and NO₆ (C_2v) coordination sphere, respectively. DC magnetic susceptibility studies for the two complexes indicate ferromagnetic interactions. Complexes 1 and 2 exhibit single-molecule magnet behavior with two-step slow relaxation processes due to the possession of inequivalent metal sites. The energy barriers of 69.19 and 45.73 K for 1, and 92.77 and 72.95 K for 2 are determined. Theoretical calculations reveal that the two-step relaxation processes in both 1 and 2 mainly originate from the single-ion magnetism of two distinct Dy(III) ions with inequivalent coordination environments.