Lang Zhao

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.

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

A dodecanuclear heterometallic dysprosium–cobalt wheel exhibiting single-molecule magnet behaviour

A novel dodecanuclear wheel with ten Dy(III) ions and two Co(II) ions bridged by four Schiff-base ligands and sixteen acetates represents the highest-nuclearity 3d-4f example of its type displaying single-molecule magnet behaviour.

Observation of slow magnetic relaxation in discrete dysprosium cubane.

A discrete dysprosium cubane has been prepared and structurally characterized. Slow relaxation of magnetization in this complex is observed, which may stimulate further investigations into the dynamics of magnetization in lanthanide clusters with different topologies.

Magnetic Properties of Dysprosium Cubanes Dictated by the M−O−M Angles of the [Dy4(μ3-OH)4] Core

Two new dysprosium(III) coordination compounds, namely, [Dy(4)(HL)(4)(C(6)H(4)NH(2)COO)(2)(mu(3)-OH)(4)(mu-OH)(2)(H(2)O)(4)].4CH(3)CN.12H(2)O (1) and Dy(8)(HL)(10)(C(6)H(4)NH(2)COO)(2)(mu(3)-OH)(8)(OH)(2)(NO(3))(2)(H(2)O)(4)] (2), have been synthesized from the Schiff-base ligand 2-{[(2-hydroxy-3-methoxyphenyl)methylidene]amino}benzoic acid (H(2)L) and dysprosium chloride (1) or dysprosium nitrate (2). Single-crystal X-ray diffraction studies reveal that compound 1 exhibits a tetranuclear cubane-like structure and that 2 is an octanuclear, bis-cubane complex. The [Dy(4)(mu (3)-OH)(4)] cubane cores of 1 and 2 are structurally related; however, the magnetic properties of 1 and 2 are drastically different. Indeed, 2 shows slow relaxation of magnetization while no out-of-phase alternating current (ac) signal is noticed for 1. These significant disparities are most likely due to the different M-O-M angles observed for the respective cubane cores.

A Dy10 Cluster Incorporates Two Sets of Vertex‐Sharing Dy3 Triangles

The study of paramagnetic metal-ion aggregates has been of increasing interest in the last three decades or so, mainly stimulated by rapid development of molecular magnetism. An area of particular interest is the investigation of single molecule magnets (SMMs) for which slow relaxation and quantum tunnelling of the magnetization is purely of molecular origin. This has led to intense activity to be able to consistently manufacture molecular structures with a finite number of interacting magnetic centres suitable for detailed magnetic study. Indeed, since the discovery in the early 1990s of the first single molecule magnet, Mn12 acetate, [2,3] a large number of compounds displaying these magnetic properties have been reported. Most of them, especially in the early years, contain only 3d ions. However, despite the large number of new molecules, no significant increase has been achieved in the blocking temperature. Recently, particular emphasis has been placed on the design of new single molecule magnets either incorporating, or made exclusively from 4f metal ions given that lanthanide ions can produce fascinating magnetic behaviour, not only through their potential to contribute high spins, but also to introduce anisotropy to a molecule as a result of the nature of the felectron shell. This magnetic anisotropy is the major component to observe the slow relaxation of the magnetization and gives the complexes by essentially different mechanism from that of the well-established 3d-based SMMs. Compared to the 3d metal SMMs, far fewer pure 4f metal SMMs have been reported. A peculiar triangular Dy cluster has attracted much interest, owing to the unusual slow relaxation behaviour in spite of the almost non-magnetic ground state. This intriguing behaviour originates from the non-collinearity of the single ion easy axes of magnetization of the Dy ions, as demonstrated by single crystal magnetic studies, as well as ab initio calculations. This peculiar chiral nature of the ground non-magnetic doublet and the resonant quantum tunnelling of the magnetization at the crossings of the discrete energy levels opens new perspectives in quantum computation and data storage in molecular nanomagnets, and thus can stimulate further investigation towards utilizing this highly anisotropic Dy3 triangle for creating novel SMMs with large blocking temperatures. We present here the constructing of Dy10 cluster of formula [Dy10ACHTUNGTRENNUNG(m3-OH)4 ACHTUNGTRENNUNG(OAc)20 ACHTUNGTRENNUNG(H2L)2ACHTUNGTRENNUNG(H3L)2ACHTUNGTRENNUNG{NH2C ACHTUNGTRENNUNG(CH2OH)3}2] with four fused Dy3 triangles by using polydentate Schiff base 2-[{(2-hydroxy-3-methoxyphenyl)methylene}amino]-2(hydroxymethyl)-1,3-propanediol (H4L). This potentially hexadentate ligand combines a tripodal group and a Schiff base group, and has previously been successfully employed to prepare 3d and 3d-4f polynuclear clusters. The reaction of dysprosium acetate with H4L in the mixture of methanol and acetonitrile in 1:4 ratio produces the Dy10 cluster of formula [Dy10ACHTUNGTRENNUNG(m3-OH)4ACHTUNGTRENNUNG(OAc)20ACHTUNGTRENNUNG(H2L)2ACHTUNGTRENNUNG(H3L)2ACHTUNGTRENNUNG{NH2C ACHTUNGTRENNUNG(CH2OH)3}2] (1), whose molecular structure determined by single-crystal X-ray diffraction is depicted in Figure 1. This neutral molecule contains four m3-OH capped triangles held together by acetate groups. Two Dy triangles are fused in a vertex-sharing fashion forming a {Dy5ACHTUNGTRENNUNG(m3OH)2} 13+ subcore. The single m3-OH capped triangle in 1 is less equilateral than that of the previously reported double m3-OH capped triangles, [12] with Dy···Dy distances 3.753, 3.788 and 3.882 for triangle A (Dy1Dy2Dy3) and 3.623, 3.870 and 3.935 for triangle B (Dy3Dy4Dy5) respectively. The dihedral angle between the two triangles A and B is 81.418. Two {Dy5 ACHTUNGTRENNUNG(m3-OH)2}13+ subcores are further linked through double acetate bridges into the Dy10 core, which is further encapsulated by four Schiff bases and two tris(hy[a] H. Ke, Dr. G.-F. Xu, Dr. L. Zhao, Prof. Dr. J. Tang, Prof. Dr. H.-J. Zhang State Key Laboratory of Rare Earth Resource Utilization Changchun Institute of Applied Chemistry Chinese Academy of Sciences Renmin Street 5625, Changchun 130022 (P.R. China) Fax: (+86)431-85262878 E-mail : tang@ciac.jl.cn hongjie@ciac.jl.cn [b] H. Ke, X.-Y. Zhang School of Material Science and Engineering Changchun University of Science and Technology Changchun 130022 (P.R. China)

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.

Syntheses, structures, and magnetic analyses of a family of heterometallic hexanuclear [Ni4M2] (M = Gd, Dy, Y) compounds: observation of slow magnetic relaxation in the Dy(III) derivative.

We described the syntheses, crystal structures, and magnetic behavior of a novel series of heterometallic [Ni(4)M(2)] [M = Gd (1), Dy (2) and Y (3)] hexanuclear compounds afforded by the reaction of rare-earth(III) nitrate, nickel(II) acetate, and Schiff-base ligand 2-(2-hydroxy-3-methoxybenzylideneamino)phenol (H(2)L) in a mixture of ethanol and dichloromethane in the presence of triethylamine. Single-crystal X-ray diffraction measurements reveal that all three compounds have a metal core made up of two Ni(2)MO(4) defective cubanes. The magnetic properties of all compounds have been studied. Solid-state direct-current magnetic susceptibility analyses demonstrate competing antiferromagnetic and ferromagnetic interactions within both compounds 1 and 3. Solid-state alternating-current magnetic susceptibility investigations show a frequency-dependent out-of-phase signal for compound 2 below 4 K, suggestive of slow magnetic relaxation.

A dodecanuclear dysprosium wheel assembled by six vertex-sharing Dy3 triangles exhibiting slow magnetic relaxation.

Reactions of lanthanide(III) (Ln(III)) perchlorate (Ln = Dy and Ho) and a polydentate Schiff base resulted in the unprecedented assembly of novel Ln(12) wheels containing six vertex-sharing Ln(3) triangles. The Dy(12) derivative represents the largest lanthanide wheel based on the peculiar Dy(3) triangles showing slow magnetic relaxation.

Hexanuclear Dysprosium(III) Compound Incorporating Vertex- and Edge-Sharing Dy3 Triangles Exhibiting Single-Molecule-Magnet Behavior

A unique hexanuclear dysprosium(III) compound with a new polydentate Schiff-base ligand shows complex slow relaxation of the magnetization most likely associated with the single-ion behavior of individual Dy(III) ions as well as the possible weak coupling between them.