Shuang-Yan Lin

Two-Step Relaxation in a Linear Tetranuclear Dysprosium(III) Aggregate Showing Single-Molecule Magnet Behavior

A well-defined two-step relaxation, described by the sum of two modified Debye functions, is observed in a new alkoxido-bridged linear tetranuclear Dy(III) aggregate showing single-molecule magnet behavior with a remarkably large energy barrier. This compound represents a model molecular aggregate with a clear two-step relaxation evidenced by frequency-dependent susceptibility, which therefore may stimulate further investigations regarding the relaxation dynamics of lanthanide-based systems.

Equatorially Coordinated Lanthanide Single Ion Magnets

The magnetic relaxation dynamics of low-coordinate Dy(III) and Er(III) complexes, namely three-coordinate ones with an equatorially coordinated triangle geometry and five-coordinate ones with a trigonal bipyramidal geometry, have been exploited for the first time. The three-coordinate Er-based complex is the first equatorially coordinated mononuclear Er-based single-molecule magnet (SMM) corroborating that simple models can effectively direct the design of target SMMs incorporating 4f-elements.

Coupling Dy3 Triangles to Maximize the Toroidal Moment

Compounds constructed by utilizing a toroidal arrangement of dipoles are attractive for applications in multiferroic materials. A toroidal arrangement of dipole moments can be envisaged, for example, by a current flowing through a solenoid bent into a torus or else by a similarly organized arrangement of magnetic dipoles. This is proposed as the primary order parameter for a multiferroic material. Recent efforts at the boundary where the description of solid-state systems meets that of molecular-based materials has revealed some interesting shifts in accepted paradigms. For example, concepts such as magnetism, magnetocaloric effects, and ferroelectrics can be viewed as properties recognizable at the condensed as well as molecular level, and there is growing interest in exploring the boundaries between these two worlds. Particularly relevant to these endeavors is the consideration of bounded (confined) metal oxide structures having toroidal moments compared with their solid-state infinite analogues. 5] On the other hand, it can also be difficult to separate purely molecular-based effects from those resulting from a resultant toroidal moment arising through a long-range interaction. The recently investigated Dy3 triangle (prototype Dy3) [7] is one of the four possible ingredients for creating multiferroic systems that should manifest two or more out of ferroelectric, ferromagnetic, ferroelastic, and ferrotoroidal behavior. Subsequently, a Dy4 single-molecule magnet (SMM), [9] a Dy6-1 SMM, [10] and a heterometallic Cu/Dy3 III 1D polymer (Dy3Cu) [4c] have been reported to show a toroidal magnetic moment in the ground state. The coupled Dy6-1 SMM that results from coupling two of the original Dy3 triangles shows enhanced relaxation dynamics compared with the precursor Dy3, [7] but the overall anisotropy and spin structure lead to a reduced toroidal magnetization. Dy3Cu is constructed by combining alternating trinuclear Dy3 SMM-building blocks and enantiopure, chiral copper(II) complexes. The discrete Dy3 triangular molecule, which can be regarded as an archetypical toroidal manifestation of an antiferromagnetic arrangement of Ising spins, has been reported and extensively investigated by us. 11] This system not only shows an essentially nonmagnetic spin ground state but also possesses a toroidal moment as described above and SMM behavior deriving from its excited states. These factors offer perspectives for the fundamental understanding and applications of quantum computation and data storage in molecular nanomagnets. The toroidal ground spin state structure analysis of the Dy3Cu system reveals that the combination of molecular chirality and the toroidal magnetism are predicted to provide multiferroic behavior only under applied fields. Thus the synthesis of compounds with utilizable large toroidal magnetic moments is a significant challenge. Given these promising results, our aim was to pursue the use of the toroidal Dy3 building block further to enhance the molecular toroidal magnetization and with the view to furthering application in multiferroics. We thus decided to focus our attention on the rearrangement of Dy3 triangles in addition to keeping in mind a systematic survey of the structural types and characteristics of compounds showing toroidal magnetic moments. Herein we report the successful combination of two Dy3 triangles in an edge-to-edge arrangement. The resulting compound shows SMM behavior with enhancement of the toroidal magnetization. In comparison to all other combinations of the Dy3 triangle that have been reported, this system is the best construction to preserve perfectly and enhance greatly the toroidal magnetization. The reaction of H3L, formed by the in situ condensation of 2,6-diformyl-4-methylphenol and ethanolamine, with Dy(NO3)3·6 H2O in the presence of triethylamine under solvothermal condition, produces pale-yellow crystals of [Dy6L4(m4-O)(NO3)4(CH3OH)]·CH3OH (1). As shown in Figure 1, the hexanuclear Dy6 core can be regarded as the linkage of two [Dy3(m3-O)2(m2-O)2] triangular units placed in an edge-toedge arrangement by one m4-O 2 ion and four deprotonated phenol oxygen atoms from four ligands. The dihedral angle between the two Dy3 planes in 1 is 29.6568, in contrast to the co-parallel planes in reported Dy6-1. Each triangular unit is [*] S. Y. Lin, Y. N. Guo, Prof. Dr. J. Tang, Dr. L. Zhao, Prof. H. J. Zhang State Key Laboratory of Rare Earth Resource Utilization Changchun Institute of Applied Chemistry, Chinese Academy of Sciences Changchun 130022 (P. R. China) E-mail: tang@ciac.jl.cn hongjie@ciac.jl.cn

Two New Dy3 Triangles with Trinuclear Circular Helicates and Their Single-Molecule Magnet Behavior

Self-assembly of polydentate Schiff base 2,6-diformyl-4-methylphenol di(benzoy1hydrazone) (H(3)L), with dysprosium thiocyanate and sodium azide, affords two novel trinuclear triangular circular helicate dysprosium(III) complexes, [Dy(3)(μ(3)-OCH(3))(2)(HL)(3)(SCN)]·4CH(3)OH·2CH(3)CN·2H(2)O (1) or [Dy(3)(μ(3)-N(3))(μ(3)-OH)(H(2)L)(3)(SCN)(3)](SCN)·3CH(3)OH·H(2)O (2), depending on the presence or absence of base. Single-crystal X-ray analyses show that two μ(3)-methoxy oxygens cap the Dy(3) triangle in complex 1 and that one μ(3)-OH and one μ(3)-N(3)(-) cap the Dy(3) triangle of complex 2, representing the first example of a μ(3)-N(3)(-)-capped lanthanide complex reported to date. Ac susceptibility measurements reveal that multiple relaxation processes and the onset of slow magnetization relaxation occur for complex 1 and 2, respectively. Theoretical calculations are required to elucidate the underlying mechanism; however, the different magnetic anisotropy of the respective structures, which is dictated by the coordination environment of Dy(III) ions and structural parameters of the triangles, is mostly responsible for the distinctive relaxation dynamics observed.

Modulating Magnetic Dynamics of Dy2 System through the Coordination Geometry and Magnetic Interaction

Two new dinuclear dysprosium compounds, [Dy2(HL1)2(PhCOO)2(CH3OH)2] (1) and [Dy2(L2)2(NO3)2(CH3OH)2]·2CH3OH·4H2O (2), have been assembled through applying two ligands with different coordination pockets. The different features of ligands H3L1 and H2L2 result in the distinct coordination geometry of the metal ions in their respective structures. The Dy ions of complexes 1 and 2 were linked by the alkoxide- and hydrazone-O, and display the hula hoop-like and the broken hula hoop-like coordination geometry, respectively. Consequently, these two compounds show distinct magnetic properties. Complex 1 behaves as a single molecule magnet (SMM) with rather slow quantum tunneling rate (τ > 274 ms), while no SMM behavior was observed for complex 2. In addition, the comparison of the structural parameters among the similar Dy2 SMMs with hula hoop-like geometry reveals the significant role played by coordination geometry and magnetic interaction in modulating the relaxation dynamics of SMMs.

Macrocyclic ligand encapsulating dysprosium triangles: axial ligands perturbed magnetic dynamics

Two Dy(3) triangles encapsulated inside the cavity of a macrocycle ligand have been successfully synthesized, providing a unique opportunity to probe the relaxation dynamics of the complexes by altering the axial ligands.

Utilizing 3d–4f Magnetic Interaction to Slow the Magnetic Relaxation of Heterometallic Complexes

The synthesis, structural characterization, and magnetic properties of four related heterometallic complexes with formulas [Dy(III)2Co(II)(C7H5O2)8]·6H2O (1), [Dy(III)2Ni(II)(C7H5O2)8]·(C7H6O2)2 (2), Tb(III)2Co(II)(C7H5O2)8 (3), and Dy(III)2Cd(II)(C7H5O2)8 (4) were reported. Each of complexes has a perfectly linear arrangement of the metal ions with two terminal Ln(III) (Ln(III) = Dy(III), Tb(III)) ions and one central M(II) (M(II) = Co(II), Ni(II), Cd(II)) ion. It was found that 1-3 displayed obvious magnetic interactions between the spin carriers according to the direct current (dc) susceptibility measurements. Alternating current (ac) magnetic susceptibility measurements indicate that complexes 1-4 all exhibit single-molecule magnet (SMM) behavior, while the replacement of the diamagnetic Cd(II) by paramagnetic ions leads to a significant slowing of the relaxation thanks to the magnetic interactions between 3d and 4f ions, resulting in higher relaxation barrier for complexes 1 and 2. Moreover, both Dy2Co and Dy2Ni compounds exhibit dual relaxation pathways that may originate from the single ion behavior of individual Dy(III) ions and the coupling between Dy(III) and Co(II)/Ni(II) ions, respectively, which can be taken as the feature of 3d-4f SMMs. The Ueff for 1 of 127 K is a relatively high value among the reported 3d-4f SMMs. The results demonstrate that the magnetic coupling between 3d and 4f ions is crucial to optimize SMM parameters. The synthetic approach illustrated in this work represents an efficient route to design nd-4f based SMMs via incorporating suitable paramagnetic 3d and even 4d and 5d ions into the d-f system.

Enantioselective Self‐Assembly of Triangular Dy3 Clusters with Single‐Molecule Magnet Behavior

Three pairs of enantiopure chiral triangular Ln3 clusters, [Ln3LRRRRRR/SSSSSS(μ3-OH)2(H2O)2(SCN)4]⋅xCH3OH⋅yH2O (R-Dy3, Ln=Dy, x=6, y=0; S-Dy3, Ln=Dy, x=6, y=1; R-Ho3, Ln=Ho, x=6, y=1; S-Ho3, Ln=Ho, x=6, y=1; R-Er3, Ln=Er, x=6, y=0; S-Er3, Ln=Er, x=6, y=1), have been successfully synthesized by a rational enantioselective synthetic strategy. The core of triangular Ln3 is bound in the central N6O3 of the macrocyclic ligand, and the coordination spheres of Ln ions are completed by four SCN(-) anions and two H2O molecules in axial positions of the macrocycle. The circular dichroism (CD) and vibrational circular dichroism (VCD) spectra of the enantiomers demonstrate that the chirality is successfully transferred from the ligands to the resulting Ln3 clusters. Ac susceptibility measurements reveal that single-molecule magnet behavior occurs for both enantiopure clusters of R-Dy3 and S-Dy3. This work is one of the few examples of the successful design of a pair of triangular Dy3 clusters showing simultaneously slow magnetic relaxation and optical activity, and this might open up new opportunities to develop novel multifunctional materials.

A triangular dysprosium with asymmetric central caps featuring ferromagnetic coupling and single-molecule magnet behaviour

A new Dy3 triangle bridged by a deprotonated alkoxyl group of a Schiff-base ligand together with a μ3-OH group has been prepared, in which intramolecular ferromagnetic interactions and single molecule magnet behaviour have been observed.