Modulating single-molecule magnet behavior towards multiple magnetic relaxation processes through structural variation in Dy4 clusters

Abstract

Three Dy₄ clusters, [Dy₄(tmhd)₈(L)₂(CH₃OH)₂]·CH₃OH (1), [Dy₄(hfac)₈(L)₂(DMF)₂]·C₇H₁₆ (2) and [Dy₄(dbm)₆(L)₂(μ₃-OH)₂]·CH₂Cl₂ (3) (tmhd = 2,2,6,6-tetramethyl-3,5-heptanedione, hfac = hexafluoroacetylacetonate, dbm = 1,3-diphenyl-1,3-propanedione, HL = 2-[(2-(hydroxyimino)propanehydrazide)methyl]), have been successfully synthesized by using three different β-diketonate salts (Dy(tmhd)₃·2H₂O, Dy(hfac)₃·2H₂O, and Dy(dbm)₃·2H₂O) to react with HL and by changing the solvent. The X-ray structural analysis shows that four Dy^III ions in clusters 1 and 2 are linearly arranged; however, cluster 3 contains one Dy₄ center with a rhombus-shaped arrangement. The different structures of three Dy₄ clusters were profoundly affected by these minor changes in β-diketonate or a change in the solvent. Magnetic studies reveal that Dy₄ clusters 1–3 exhibit different single-molecule magnet (SMM) behaviors under a zero dc field. 1 and 2 display slow magnetic relaxation behaviors with effective energy barriers ΔE/k_B = 1.44 K for 1 and ΔE/k_B = 50.96 K for 2, while for 3, two distinct slow magnetic relaxation processes are observed, with effective energy barriers ΔE/k_B = 40.45 K for the fast relaxation process and ΔE/k_B = 113.63 K for the slow relaxation process. This study shows that the β-diketonate coligands play an important role in modulating molecular structures and further affecting the magnetic dynamics of the lanthanide clusters towards multiple magnetic relaxation processes.