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 1,2-bis(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 (2:...

Computational Studies on SAMs of {Mn6} SMMs on Au(111): Do Properties Change upon Grafting?

“…The surface-molecule interaction in many cases lead to the loss of SMM characteristics and this has been witnessed in a variety of cases including the archetypal {Mn 12 } SMM. 10 Recently using a long chain alkyl thiols a {Fe 4 } SMM has been organized on Au (111) surface and its SMM features on Au(111) surface have been observed using XMCD studies.…”

“…The reversal of magnetization in SMMs is hampered by a barrier reversal whose height is given by |D|S 2 for integer spin systems with S being the spin ground state and D a negative axial anisotropy parameter. 3 For {Mn 12 } family of complexes the theoretical barrier height is estimated to be 60 K. Recently many lanthanide complexes reported to have higher barrier height, 4 in particular a {Dy 5 (III)} cluster with a barrier of 540 K. 5 Moreover monomeric Tb(III) complex with phthalocyaninate ligands reported to have a barrier height of about 800 K, 6 the largest known for such class of molecules. However, in most lanthanide based SMMs the quantum tunneling of magnetization is very fast leading the very small coercitivity in the hysteresis loop, a remarkable exception being the lanthanide dimers bridged by the N 3 -radical 7,8 Regarding clusters of transition metal complexes, a breakthrough has been achieved with the discovery of a family of {Mn 6 } complexes [Mn(III) 6 O 2 (sao) 6 (O 2 C-th) 2 L 4-6 ], 9 where HO 2 C-ph=3-phenil carboxylic acid, L = EtOH, H 2 O, possessing a barrier height of ca.…”

Giant magnetic anisotropy and tunnelling of the magnetization in Li2(Li1−xFex)N

“…Basic magnetic units of SMMs are transition metal ion clusters 9 , lanthanide ion clusters 10,11 or mixed clusters of both 12 . Even mononuclear complexes based on a single lanthanide ion have been realized 13,14 .…”

Modulating the magnetic relaxation of lanthanide-based single-molecule magnets

“…Further, more flexible polydentate ligands could be applied for the polynuclear Lanthanide-based SMMs [34,35]. Consequently, the complicated multiple relaxation processes, which are most likely associated with distinct anisotropic centers due to the different crystal field environments, have been increasingly identified in a weakly coupled lanthanide system [20,21]. It is therefore possible to "fine-tune" the magnetic properties of lanthanide complexes through the alteration of different ligand fields.…”

“…However, theoretical study based on experiments suggests that large magnetic anisotropy is not helped by a high spin state of the ground state for transition-metal systems, which has been a crucial roadblock to obtaining systems with larger energy barriers [12,13]. Nevertheless, since Ishikawa et al [14] discovered lanthanide double-decker complexes [Pc 2 Ln] − TBA + (Ln = Tb III , Dy III , Ho III ; TBA + = N(C 4 H 9 ) + ) functioning as very efficient SMMs, the complexes containing lanthanide elements are highlighted and large numbers of Lanthanide-based Single Molecule Magnets (Ln-SMMs) with larger energy barriers have evolved, especially Dy-based complexes with various nuclearities from Dy 1 [15], Dy 2 [16,17], Dy 3 [18,19], Dy 4 [20,21], Dy 6 [22], Dy 10 [23] to Dy 26 [24]. These systems may hold the key to obtaining high anisotropic barrier single-molecule magnets (SMMs).…”