The magnet-like behavior can beobserved by slow relaxation of the magnetization below theblocking temperature. Since the discovery of SMMs in theearly 1990s, this assumption has formed the basis for theunderstanding of the origin of the anisotropic barrier.However, in recent years the development of novel lantha-nide-only SMMs that challenge and defy this theory pose anumber of questions:

A Polynuclear Lanthanide Single-Molecule Magnet with a Record

Molecular magnetism of lanthanide: Advances and perspectives

The promising potential applications, such as information processing and storage or molecular spintronics, of single-molecule magnets (SMMs) have spurred on the research of new, better SMMs. In this context, lanthanide ions have been seen as ideal candidates for new heterometallic transition metal–lanthanide SMMs. This perspective reviews 3d–4f SMMs up to 2014 and highlights the most significant advances and challenges of the field.

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Heterometallic 3d–4f single-molecule magnets

Single-ion magnets (SIMs), exhibiting slow magnetization relaxation in the absence of the magnetic field, originate from their single spin-carrier centre. In pursuit of high-performance magnetic properties, such as high spin-reversal barrier and high blocking temperature, various metal centres were investigated to establish SIMs, including 3d and 5d transition metal ions, 4f lanthanide ions, and 5f actinide ions, which possess unique zero-field splitting and magnetic properties. Therefore, proper ligand field is of great importance to different types of metals. In the given great breakthroughs since the first SIM, [Pc2 Tb]- (Pc=dianion of phthalocyanine), was reported, strategies of ligand field design have emerged. In this review, the developments of SIMs with different metal centres are summarized, as well as the possible strategies.

Single Ion Magnets from 3d to 5f: Developments and Strategies.

The employment of a multidentate salicylamide salen-like ligand, 2-hydroxy-N-(2-(2-hydroxybenzylidene)amino)ethyl)benzamide (H3L), in aid of NO3− anions under weak basic conditions in ZnII–LnIII chemistry (Ln = Eu, 1 and Dy, 2) led to the isolation of two novel butterfly heterometallic dodecanuclear clusters with six LnIII ions occupying the body position and six ZnII ions the outer wing-tip sites. All of them are fully characterized by elemental analysis, FT-IR spectroscopy, TG analysis, single-crystal X-ray diffraction, and X-ray powder diffraction (XRPD) techniques. Luminescence studies indicate that 1 exhibits dual emission, while 2 exhibits a bright blue emission under visible light excitation. Furthermore, magnetic susceptibility studies carried out for 2 indicate that the magnetic exchange between DyIII ions revealed ferromagnetic interactions with interesting slow relaxation of magnetization of the SMM behavior.

Two dodecanuclear heterometallic [Zn6Ln6] clusters constructed by a multidentate salicylamide salen-like ligand: synthesis, structure, luminescence and magnetic properties

A planar triangular Dy3 + Dy3 single-molecule magnet with a toroidal magnetic moment

Design and synthesis of air-stable and easily tailored high-performance single-molecule magnets (SMMs) are of great significance toward the implementation of SMMs in molecular-based magneto-electronic devices. Here, by introducing electron-withdrawing fluorinated substituents on equatorial ligand, two chiral Dy(III) macrocyclic complexes, RRRR-Dy-D6hF12 (1) and SSSS-Dy-D6hF12 (2), with a record anisotropy barrier exceeding 1800 K and the longest relaxation time approaching 2500 s at 2.0 K for all known air-stable SMMs, were obtained. The nearly perfect axiality of the ground Kramers doublet (KD) enables the open hysteresis loops up to 20 K in the magnetically diluted sample. It is notable that they are structurally rigid with high thermal stability and the apical ligand can be tailored to carry proper surface-binding groups. This finding not only improves the magnetic properties for air-stable SMMs but also provides a new avenue for deposition of SMMs on surfaces.

Air-Stable Chiral Single-Molecule Magnets with Record Anisotropy Barrier Exceeding 1800 K.

The self-assembly of three giant hexagonal 3d–4f metallocycles with inner diameters of 16.4, 16.5, and 16.4 A, is described. Hexagonal metallocycles were stacked along the crystallographic c axis, producing unique hexagonal macroscopic tubular single crystals. The assembly mechanism of the tubular crystals was investigated. Remarkably, all three hexagonal metallocycles show typical single-molecule magnet behavior, benefiting from the ferromagnetic couplings between the 3d and 4f ions.

Xiao-Lei Li

Papers

Molecular magnetism of lanthanide: Advances and perspectives

A planar triangular Dy3 + Dy3 single-molecule magnet with a toroidal magnetic moment

Air-Stable Chiral Single-Molecule Magnets with Record Anisotropy Barrier Exceeding 1800 K.

Macroscopic Hexagonal Tubes of 3 d–4 f Metallocycles

End-to-end azido-pinned interlocking lanthanide squares.