Yun-Nan Guo

Strong Axiality and Ising Exchange Interaction Suppress Zero-Field Tunneling of Magnetization of an Asymmetric Dy2 Single-Molecule Magnet

The high axiality and Ising exchange interaction efficiently suppress quantum tunneling of magnetization of an asymmetric dinuclear Dy(III) complex, as revealed by combined experimental and theoretical investigations. Two distinct regimes of blockage of magnetization, one originating from the blockage at individual Dy sites and the other due to the exchange interaction between the sites, are separated for the first time. The latter contribution is found to be crucial, allowing an increase of the relaxation time by 3 orders of magnitude.

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.

Modulating magnetic dynamics of three Dy2 complexes through keto-enol tautomerism of the o-vanillin picolinoylhydrazone ligand.

Complexation of dysprosium(III) with the heterodonor chelating ligand o-vanillin picolinoylhydrazone (H(2)ovph) in the presence of different bases affords three new dinuclear dysprosium(III) coordination compounds, namely, [Dy(2)(ovph)(2)(NO(3))(2)(H(2)O)(2)]·2H(2)O (1), [Dy(2)(Hovph)(ovph)(NO(3))(2)(H(2)O)(4)]·NO(3)·2CH(3)OH·3H(2)O (2), and Na[Dy(2)(Hovph)(2)(μ(2)-OH)(OH)(H(2)O)(5)]·3Cl·3H(2)O (3), where the aroylhydrazone ligand adopts different coordination modes in respective structures depending on the reaction conditions, as revealed by single-crystal X-ray analyses to be due to their tautomeric maneuver. The magnetic properties of 1-3 are drastically distinct. Compounds 1 and 2 show single-molecule-magnet behavior, while no out-of-phase alternating-current signal is noticed for 3. The structural differences induced by the different coordinate fashions of the ligand may influence the strength of the local crystal field, the magnetic interactions between metal centers, and the local tensor of anisotropy on each Dy site and their relative orientations, therefore generating dissimilar dynamic magnetic behavior.

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.

An NCN-pincer ligand dysprosium single-ion magnet showing magnetic relaxation via the second excited state

Single-molecule magnets are compounds that exhibit magnetic bistability purely of molecular origin. The control of anisotropy and suppression of quantum tunneling to obtain a comprehensive picture of the relaxation pathway manifold, is of utmost importance with the ultimate goal of slowing the relaxation dynamics within single-molecule magnets to facilitate their potential applications. Combined ab initio calculations and detailed magnetization dynamics studies reveal the unprecedented relaxation mediated via the second excited state within a new DyNCN system comprising a valence-localized carbon coordinated to a single dysprosium(III) ion. The essentially C2v symmetry of the DyIII ion results in a new relaxation mechanism, hitherto unknown for mononuclear DyIII complexes, opening new perspectives for means of enhancing the anisotropy contribution to the spin-relaxation barrier.

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.

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.

Two Bulky-Decorated Triangular Dysprosium Aggregates Conserving Vortex-Spin Structure

The self-assembly of dysprosium(III) with the tailored chemical modification of the vanillin group affords two decorated Dy(3) compounds, namely, [Dy(3)(μ(3)-OH)(2)(Hpovh(-))(3)(NO(3))(3)(CH(3)OH)(2)H(2)O]·NO(3)·3CH(3)OH·2H(2)O (2) and [Dy(3)(μ(3)-OH)(2)(H(2)vovh(-))(3)Cl(2)(CH(3)OH)(H(2)O)(3)][Dy(3)(μ(3)-OH)(2)(H(2)vovh(-))(3)Cl(2)(H(2)O)(4)]·Cl(4)·2CH(3)OH·2CH(3)CN·7H(2)O (3), where H(2)povh = N-(pyridylmethylene)-o-vanilloylhydrazone and H(3)vovh = N-vanillidene-o-vanilloylhydrazone. Of particular interest is that those two title Dy(3) compounds maintain the peculiar vortex-spin structure of the ground nonmagnetic doublet. Complex 2 displays frequency-dependent slow magnetic relaxation, while 3 still inherits the single-molecule-magnet behavior as the parent Dy(3) prototype. The dissimilar dynamic magnetic behavior originates from the structural differences in light of the coordination environment of Dy(III) ions, which influence the local tensor of anisotropy and crystal-field splitting on each Dy site.

Heterometallic cubanes: syntheses, structures, and magnetic properties of lanthanide(III)-nickel(II) architectures.

Reactions of lanthanide(III) perchlorate (Ln = Dy, Tb, and Gd), nickel(II) acetate, and ditopic ligand 2-(benzothiazol-2-ylhydrazonomethyl)-6-methoxyphenol (H(2)L) in a mixture of methanol and acetone in the presence of NaOH resulted in the successful assembly of novel Ln(2)Ni(2) heterometallic clusters representing a new heterometallic 3d-4f motif. Single-crystal X-ray diffraction reveals that all compounds are isostructural, with the central core composed of distorted [Ln(2)Ni(2)O(4)] cubanes of the general formula [Ln(2)Ni(2)(μ(3)-OH)(2)(OH)(OAc)(4)(HL)(2)(MeOH)(3)](ClO(4))·3MeOH [Ln = Dy (1), Tb (2), and Gd (3)]. The magnetic properties of all compounds have been investigated. Magnetic analysis on compound 3 indicates ferromagnetic Gd···Ni exchange interactions competing with antiferromagnetic Ni···Ni interactions. Compound 1 displays slow relaxation of magnetization, which is largely attributed to the presence of the anisotropic Dy(III) ions, and thus represents a new discrete [Dy(2)Ni(2)] heterometallic cubane exhibiting probable single-molecule magnetic behavior.