A Polynuclear Lanthanide Single‐Molecule Magnet with a Record Anisotropic Barrier

Abstract

Dedicated to Professor Annie K. Powell on the occasion of her 50th birthday Single-molecule magnets (SMMs) continue to be an attractive research field because of their unique and intriguing properties and potential applications in high-density data storage technologies and molecular spintronics. [1] The anisotropic barrier (U) of an SMM is derived from a combination of an appreciable spin ground state (S) and uniaxial Ising-like magneto-anisotropy (D). [2] The magnet-like behavior can be observed by slow relaxation of the magnetization below the blocking temperature. Since the discovery of SMMs in the early 1990s, this assumption has formed the basis for the understanding of the origin of the anisotropic barrier. However, in recent years the development of novel lanthanide-only SMMs that challenge and defy this theory pose a number of questions: [3] How can slow relaxation of the magnetization be observed in a nonmagnetic state complex? Why are large energy barriers seen for mononuclear lanthanide(III) complexes? To answer such important questions, it is vital to investigate novel SMMs with high magnetoanisotropy for which the influence of the large negative D value could result in higher anisotropic barriers. [4] Clearly lanthanide-based polynuclear systems are an important avenue to explore in the pursuit of SMMs with higher anisotropic barriers, because of the strong spin-orbit coupling commonly observed in 4f systems. [3][4][5] However, lanthanide-only SMMs are rare. [3,5] The majority of reported SMMs have been prepared with transition-metal ions, [2] although the recent application of a mixed transition-metal/ lanthanide strategy also yielded many structurally and magnetically interesting systems. [6] The scarcity of lanthanide-only SMMs results from the difficulty in promoting magnetic interactions between the lanthanide ions. The interactions can, however, be enhanced by overlapping bridging ligand orbitals. In addition, fast quantum tunneling of the magnetization (QTM), which is common for lanthanide systems, generally prevents the isolation of SMMs with high anisotropic energy barriers.Our recent work suggests [5a-c] that dysprosium(III) ions may hold the key to obtaining high-blocking-temperature lanthanide-only SMMs. When an appropriate ligand system is employed, it is possible to exploit the large intrinsic magnetoanisotropy, high spin, and reduced QTM that dysprosium(III) ions offer. Recently, we have focused our attention towards the synthesis of dysprosium(III) cluster complexes with 1,2bis(2-hydroxy-3-methoxybenzylidene) hydrazone (H 2 bmh) and 3-methoxysalicylaldehyde hydrazone (Hmsh) as chelating agents (see Figure S1 in the Supporting Information). This strategy has proven to be successful and has led to a polynuclear lanthanide SMM with a record anisotropic barrier. Herein, we report the synthesis, structure, and magnetism of a tetranuclear dysprosium(III) SMM that exhibits the largest relaxation barrier seen for any polynuclear SMM to date.A suspension of DyCl 3 ·6H 2 O and o-vanillin...

Trinuclear [CoIII2–LnIII] (Ln=Tb, Dy) Single‐Ion Magnets with Mixed 6‐Chloro‐2‐Hydroxypyridine and Schiff Base Ligands

“…The ac oscillating frequencies corresponding to the observed peak temperatures were also fitted to the Arrhenius law, which gave a U eff value of 32.3A C H T U N G T R E N N U N G (2.6) K and a t 0 value of 2.5A C H T U N G T R E N N U N G (1.1) 10 À10 s (Figure 7). The t 0 value is also in the normal range for SMMs/SIMs, [4][5][6][7][8][9][10] but it is remarkably smaller than that of 1 (5.6 10 À6 s), and the U eff value of 2 (32.3 K) is clearly smaller than that of 1 (74.1 K). Further research into the dynamic magnetic behavior of 2 in the form of c'' versus c' plots are shown in Figure 8.…”

“…À11 s for known SMMs/SIMs; [4][5][6][7][8][9][10] the U eff value is comparable to that of the star molecule Mn 12 [1] and is remarkably larger than that of the […”

“…[2k] Much attention has been paid to the design and construction of pure 4f SMMs/SIMs [4] and 3d-4f SMMs/ SIMs in which manganese, [5] iron, [6] cobalt, [7] nickel, [8] and copper [9] generally act as the 3d metal. Strikingly, although most of the reported lanthanide SIMs are mononuclear complexes, recent research suggested that SIMs could be constructed from a lanthanide ion upon combination with one or more diamagnetic metal ions.…”

Lanthanide Antimony Oxohalides: From Discrete Nanoclusters to Inorganic–Organic Hybrid Chains and Layers

“…The structures were solved by direct methods and refined by full-matrix least-squares analysis on F 2 using the SHELXL97 program package. CCDC 822912 (1), 822913 (2), and 822914 (3) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/ data_request/cif.…”

“…[2] Recently, high-nuclearity clusters as secondary building units (SBUs) acting as nodes have been introduced to construct diversiform inorganic-organic hybrid structures with organic ligands with different geometry as linkers. [3] Clusters as rigid SBUs, especially expanded to nanometer sizes, are better than single metal ion nodes at maintaining specific geometries and imparting physical properties to hybrids through the assembly process.…”