Interplay between anisotropy and magnetic exchange to modulate the magnetic relaxation behaviours of phenoxo bridged Dy2 dimers with axial β-diketonate co-ligands

Abstract

A series of Schiff base LH ((E)-2-((pyridin-2-ylmethylene)amino)phenol) supported phenoxo bridged symmetric [Dy₂(L)₂(hfac)₄] (1), [Dy₂(L)₂(tfac)₄] (2) and asymmetric [Dy₂(L)₂(thd)₃(NO₃)]·1.5H₂O (3) binuclear complexes were isolated using differently substituted β-diketonate co-ligands (Hhfac = hexafluoroacetylacetonate, Htfac = trifluoroacetylacetonate, and Hthd = 2,2,6,6-tetramethyl-3,5-heptanedione). In all the three complexes 1–3, the two LH ligands provide phenoxo bridging and N-donor atoms. The {Dy₂(μ₂-O)₂} magnetic core structures with LH ligands are found to be the same in 1–3 while the dissimilar functionalities of the axially coordinated different β-diketonate co-ligands play a crucial role in modulating the magnetic anisotropy of individual Dy^III sites and magnetic exchange between them. The experimental static magnetic behaviour suggests the presence of intramolecular antiferromagnetic interactions in all the three complexes 1–3. The strength of the magnetic exchange coupling decreases with increasing magnetic anisotropy of individual Dy^III ions from complex 1 to complex 3 and simultaneously their zero-field slow magnetic relaxation behaviors were found to increase with effective energy barriers (ΔE/k_B) of 9.04 K, 24.06 K and 25.65 K, respectively. Furthermore, the DFT and ab initio theoretical calculations performed on the X-ray structures of complexes 1–3 support our experimental findings.