Yan-Cong Chen

A Stable Pentagonal Bipyramidal Dy(III) Single-Ion Magnet with a Record Magnetization Reversal Barrier over 1000 K

Single-molecule magnets (SMMs) with a large spin reversal barrier have been recognized to exhibit slow magnetic relaxation that can lead to a magnetic hysteresis loop. Synthesis of highly stable SMMs with both large energy barriers and significantly slow relaxation times is challenging. Here, we report two highly stable and neutral Dy(III) classical coordination compounds with pentagonal bipyramidal local geometry that exhibit SMM behavior. Weak intermolecular interactions in the undiluted single crystals are first observed for mononuclear lanthanide SMMs by micro-SQUID measurements. The investigation of magnetic relaxation reveals the thermally activated quantum tunneling of magnetization through the third excited Kramers doublet, owing to the increased axial magnetic anisotropy and weaker transverse magnetic anisotropy. As a result, pronounced magnetic hysteresis loops up to 14 K are observed, and the effective energy barrier (Ueff = 1025 K) for relaxation of magnetization reached a breakthrough among the SMMs.

Symmetry-Supported Magnetic Blocking at 20 K in Pentagonal Bipyramidal Dy(III) Single-Ion Magnets

Single-molecule magnets (SMMs) that can be trapped in one of the bistable magnetic states separated by an energy barrier are among the most promising candidates for high-density information storage, quantum processing, and spintronics. To date, a considerable series of achievements have been made. However, the presence of fast quantum tunnelling of magnetization (QTM) in most SMMs, especially in single-ion magnets (SIMs), provides a rapid relaxation route and often sets up a limit for the relaxation time. Here, we pursue the pentagonal bipyramidal symmetry to suppress the QTM and present pentagonal bipyramidal Dy(III) SIMs [Dy(Cy3PO)2(H2O)5]Cl3·(Cy3PO)·H2O·EtOH (1) and [Dy(Cy3PO)2(H2O)5]Br3·2(Cy3PO)·2H2O·2EtOH (2), (Cy3PO = tricyclohexyl phosphine oxide). Magnetic characterizations reveal their fascinating SMM properties with high energy barriers as 472(7) K for 1 and 543(2) K for 2, along with a record magnetic hysteresis temperature up to 20 K for 2. These results, combined with the ab initio calculations, offer an illuminating insight into the vast possibility and potential of what the symmetry rules can achieve in molecular magnetism.

Switching the anisotropy barrier of a single-ion magnet by symmetry change from quasi-D5h to quasi-Oh

A reversible single-crystal-to-single-crystal transformation is used to dramatically change the relaxation behavior of a single-ion magnet. The coordination geometry of the DyIII site of a [Zn–Dy–Zn] complex changes from pentagonal–bipyramid (quasi-D5h) to octahedron (quasi-Oh), inducing an energy barrier change from 305 cm−1 (439 K) to a negligible value, respectively. Ab initio calculations reveal that the ideal D5h–DyIII is of perfect axiality with a substantial energy barrier in accordance with the experimental result.

A Dysprosium Metallocene Single‐Molecule Magnet Functioning at the Axial Limit

Abstraction of a chloride ligand from the dysprosium metallocene [(Cpttt )2 DyCl] (1Dy Cpttt =1,2,4-tri(tert-butyl)cyclopentadienide) by the triethylsilylium cation produces the first base-free rare-earth metallocenium cation [(Cpttt )2 Dy]+ (2Dy ) as a salt of the non-coordinating [B(C6 F5 )4 ]- anion. Magnetic measurements reveal that [2Dy ][B(C6 F5 )4 ] is an SMM with a record anisotropy barrier up to 1277 cm-1 (1837 K) in zero field and a record magnetic blocking temperature of 60 K, including hysteresis with coercivity. The exceptional magnetic axiality of 2Dy is further highlighted by computational studies, which reveal this system to be the first lanthanide SMM in which all low-lying Kramers doublets correspond to a well-defined MJ value, with no significant mixing even in the higher doublets.

A Heterometallic FeII–DyIII Single‐Molecule Magnet with a Record Anisotropy Barrier

A record anisotropy barrier (319 cm(-1) ) for all d-f complexes was observed for a unique Fe(II) -Dy(III) -Fe(II) single-molecule magnet (SMM), which possesses two asymmetric and distorted Fe(II) ions and one quasi-D5h Dy(III) ion. The frozen magnetization of the Dy(III) ion leads to the decreased Fe(II) relaxation rates evident in the Mössbauer spectrum. Ab initio calculations suggest that tunneling is interrupted effectively thanks to the exchange doublets.

Study of a magnetic-cooling material Gd(OH)CO3

The magnetocaloric effect of a coordination polymeric material with a repeating unit of Gd(OH)CO3 has been studied experimentally using isothermal magnetization and heat capacity measurements. The maximum entropy change, −ΔSm, reaches 66.4 J kg−1 K−1 or 355 mJ cm−3 K−1 for ΔH = 7 T and T = 1.8 K. Density functional theory (DFT) calculations show weak and competing antiferromagnetic interactions between the metal centres.

CuIIGdIII Cryogenic Magnetic Refrigerants and Cu8Dy9 Single‐Molecule Magnet Generated by In Situ Reactions of Picolinaldehyde and Acetylpyridine: Experimental and Theoretical Study

A series of heterometallic [Ln(III)(x)Cu(II)(y)] complexes, [Gd2Cu2]n (1), [Gd4Cu8] (2), [Ln9Cu8] (Ln=Gd, 3·Gd; Ln=Dy, 3·Dy), were successfully synthesized by a one-pot route at room temperature with three kinds of in situ carbonyl-related reactions: Cannizzaro reaction, aldol reaction, and oxidation. This strategy led to dysprosium analogues that behaved as single-molecule magnets (SMMs) and gadolinium analogues that showed significant magnetocaloric effect (MCE). In this study a numerical DFT approach is proposed by using pseudopotentials to calculate the exchange coupling constants in three polynuclear [Gd(x)Cu(y)] complexes; with these values exact diagonalization or quantum Monte Carlo simulations have been performed to calculate the variation of the magnetic entropy involved in the MCE. For the [Dy9Cu8] complexes, local magnetic properties of the Dy(III) centers have been determined by using the CASSCF+RASSI method.

Multifunctional DyIII4 Cluster Exhibiting White‐Emitting, Ferroelectric and Single‐Molecule Magnet Behavior

Significant attention has been paid to the investigation of single-molecule magnets (SMMs) since the first Mn12 cluster with such properties was reported in 1993. During the past two decades, SMMs have experienced three generations of development, from the initially studied 3d metal clusters to mixed 3d–4f clusters, and now to 4f-based species. The drastically increased interest in 4f-based SMMs is because of their significant magnetic anisotropy originating from large unquenched orbital angular momenta. On the other hand, lanthanide-based complexes are also the subject of intense investigation as luminescent materials as a result of their large Stokes shifts and the very narrow emission bands observed. Recently, some pioneering studies have combined both properties to improve the performance and enlarge the application scope. A few Dy and Yb complexes have recently been shown to be luminescent SMMs. To further miniaturize molecule-based devices, multifunctional SMMs combining versatile physical properties, such as ferroelectricity, dielectricity, and chirality may be useful. The large inherent anisotropy of the Dy ion has made it an ideal candidate for the manufacture of a series of SMMs. Additionally, Dy can function as a yellow-light emitter. The combination of a yellow-emitting Dy unit and a blueemitting organic chromophore will result in dual-color Y/B emission from a single molecule that can be used to generate white-light emission. At the same time, the blue-lightemitting ligand (Figure S1 in the Supporting Information), 3,5-bis(pyridin-2-yl)-1,2,4-trizole (Hbpt), exhibits potential chirality because of the presence of torsion angles between aromatic rings, which may lead to a chiral structure from the Dy–Hbpt reaction system. Following the above-designed strategy, solvothermal reactions of DyACHTUNGTRENNUNG(NO3)3, Hbpt, and NEt3 have been carried out in different solvents. Luckily, colorless block-shaped crystals of chiral complex 1 (D-1 and L-1 are the two enantiomers), [Dy4ACHTUNGTRENNUNG(m-bpt)4ACHTUNGTRENNUNG(m3-OH)2ACHTUNGTRENNUNG(m-OMe)2ACHTUNGTRENNUNG(NO3)4]·3 MeOH, were obtained from a solution in methanol at 120 8C, which are very different from those obtained from solutions in ethanol. The phase purity of bulk 1 was confirmed by comparison of its powder diffraction pattern with that calculated from the single crystal study (Figure S2 in the Supporting Information). Single-crystal X-ray structure analysis reveals that complex 1 crystallizes in the monoclinic space group P21. The molecular structures are depicted in Figure 1 and show that all Dy ions possess distorted square-antiprismatic geometries with N4O4 coordination environments (Figure S3 in the

Symmetry-Related [LnIII6MnIII12] Clusters toward Single-Molecule Magnets and Cryogenic Magnetic Refrigerants

A family of high-nuclearity [Ln(III)(6)Mn(III)(12)] (Ln = Gd, Tb) nanomagnets has been synthesized, of which two are in D(2) molecular symmetry and the other two are in C(1) symmetry. X-ray crystallography shows that each of them contains a similar {Mn(III)(8)O(13)} unit, four marginal Mn(III) ions, and two linear {Ln(III)(3)} units with parallel or perpendicular orientation for high- and low-symmetry cores, respectively. For [Gd(III)(6)Mn(III)(12)], the distinct spins of the {Mn(III)(8)O(13)} unit lead to different spin ground states (S(T) = 23 for the high-symmetry one and S(T) = 16 for the low-symmetry one), and significant magnetocaloric effects are observed in a wide temperature range [full width at half-maximum (FWHM) of -ΔS(m) > 18 K] that can maximizes the refrigerant capacity, which may be attributed to the ferromagnetic interactions. By replacement of isotropic Gd(III) with anisotropic Tb(III), they behave as single-molecule magnets, with the high-symmetry one possessing a larger effective barrier (36.6 K) than the low-symmetry one (19.6 K).

Hyperfine-Interaction-Driven Suppression of Quantum Tunneling at Zero Field in a Holmium(III) Single-Ion Magnet

An extremely rare non-Kramers holmium(III) single-ion magnet (SIM) is reported to be stabilized in the pentagonal-bipyramidal geometry by a phosphine oxide with a high energy barrier of 237(4) cm-1 . The suppression of the quantum tunneling of magnetization (QTM) at zero field and the hyperfine structures originating from field-induced QTMs can be observed even from the field-dependent alternating-current magnetic susceptibility in addition to single-crystal hysteresis loops. These dramatic dynamics were attributed to the combination of the favorable crystal-field environment and the hyperfine interactions arising from 165 Ho (I=7/2) with a natural abundance of 100 %.