A salen-type Dy₄ single-molecule magnet with an enhanced energy barrier and its analogues

Abstract

Four isomorphic tetranuclear lanthanide complexes, namely [Ln4(L)2(HL)2(NO3)2(OH)2](NO3)2·4H2O (Ln = Dy (1); Tb (2); Ho (3); Er (4)), constructed using hexadentate salen-type ligand N,N'-bis(3-methoxy-salicylidene)cyclohexane-1,2-diamine, have been isolated. X-ray crystallographic analysis reveals that all of the complexes 1-4 are of discrete tetranuclear structure with a unique {Ln4O8} core in which four lanthanide ions are coplanar in a rhombic frame. There are two crystallographically unequivalent lanthanide ions, that is the Ln1(III) ion which is nine-coordinated in a monocapped square-antiprismatic geometry of the C(4v) point group and the Ln2(III) ion which is eight-coordinated in a distorted bicapped trigonal-prismatic geometry of the C(2v) point group. Magnetic analysis reveals that complex 1 exhibits two slow magnetic relaxations with the highest energy barrier among the reported tetranuclear salen-type dysprosium SMMs. This further extends the available SMMs of salen-type lanthanide complexes.

Tuning the Magnetic Interactions in Dy(III)4 Single-Molecule Magnets

“…Powder X-ray diffraction (PXRD) patterns match well with those calculated using the single-crystal X-ray data, which confirms the formulations and phase purity of the bulk product ( Figure S1 in the Supporting Information). [32][33][39][40][41][42] while in some unusual cases, two metal sites are sevencoordinated with two being eight-coordinated, 43 two eight with two nine, [44][45] and two nine with two ten. 46 Thus the present complex adds another example into this unusual catalog.…”

Substitution Effects Regulate the Formation of Butterfly-Shaped Tetranuclear Dy(III) Cluster and Dy-Based Hydrogen-Bonded Helix Frameworks: Structure and Magnetic Properties

“…At 300 K, the observed χ m T product of Dy 4 is 52.41 cm 3 K mol −1 , which is slightly higher than the expected theoretical value of 56.68 cm 3 K mol −1 for four isolated Dy III ions. 84−87,89−98 The χ m T values of Dy 4 gradually decrease with decreasing temperature at about 50 K and then decrease sharply to reach a minimum of 42.01 cm 3 K mol −1 at 2 K. 84 The behavior of χ m T values of Dy 4 is caused by zero field splitting, Zeeman effects, significant magnetic anisotropy of the Dy(III) ions, and thermal depopulation of the Stark sublevels. Dy 4 magnetization was measured and exhibited a sharp increase in the low-field range and then a slow increase in the high-field range (Figure S4b), indicating the presence of low-lying energy states and/or anisotropy in Dy 4 .…”

“…In the high-temperature range, we applied an Orbach relaxation process and obtained U eff = 41.24 K and τ 0 = 3.39 × 10 −8 s. When we considered the Raman and Orbach processes (τ −1 = τ 0 −1 exp(−U eff /k B T) + CT n ) to fit Dy 4 at all of the temperatures, we obtained U eff = 50.93 K and τ 0 = 6.18 × 10 −9 s (Figures 5b). 84 No obvious hysteresis curve of Dy 4 was observed due to the strong quantum tunneling effect of Dy(III) ions (Figure S6). Magnetic Property Analysis of Dy-HHFs.…”

Salen-type mononuclear dysprosium complex displays significant single-molecule magnet performance

“…have been applied to construct lanthanide-based SMMs. Among these ligands, the salen-type and its derivatives possessing multidentate coordination sites, easily afforded by the condensation of salicylaldehyde and diamine, have been extensively employed to synthesize numerous mononuclear, 28,32–34 dinuclear, 35–37 and polynuclear 38–40 SMMs. However, developing salen-type mononuclear lanthanide complexes with higher energy barriers and hysteresis loops and studying their magnetism–structure relationship remain a great challenge.…”