Quan-Wen Li

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.

A zigzag DyIII4 cluster exhibiting single-molecule magnet, ferroelectric and white-light emitting properties

A novel multifunctional complex [Dy4(OH)2(bpt)4(NO3)6(EtOH)2]·EtOH (1, Hbpt = 3,5-bis(pyridin-2-yl)-1,2,4-trizolate) was designed, based on the self-assembly under hydrothermal conditions, and it displays properties of single-molecule magnets (SMMs), white-light emission and ferroelectricity. Studies of static and dynamic magnetism reveal the SMMs behaviour of 1 with energy barrier Ueff = 43.22(8) K. Furthermore, the strategy of a dichromatic mixture of blue (bpt−) and yellow (Dy3+) emissive colours was utilized to obtain white-light emission through modulation of the excitation wavelength. This strategy has been worked up to create lanthanide-based fluorescent molecular magnets recently. Moreover, ferroelectricity, a “plus” feature, was added to the cluster as a result of the polar point group C2v.

Dynamic Magnetic and Optical Insight into a High Performance Pentagonal Bipyramidal DyIII Single-Ion Magnet

The pentagonal bipyramidal single-ion magnets (SIMs) are among the most attractive prototypes of high-performance single-molecule magnets (SMMs). Here, a fluorescence-active phosphine oxide ligand CyPh2 PO (=cyclohexyl(diphenyl)phosphine oxide) was introduced into [Dy(CyPh2 PO)2 (H2 O)5 ]Br3 ⋅2 (CyPh2 PO)⋅EtOH⋅3 H2 O, and combined dynamic magnetic measurement, optical characterization, ab initio calculation, and magneto-optical correlation of this high-performance pseudo-D5h DyIII SIM with large Ueff (508(2) K) and high magnetic hysteresis temperature (19 K) were performed. This work provides a deeper insight into the rational design of promising molecular magnets.

The effect of magnetic coupling on magneto-caloric behaviour in two 3D Gd(III)–glycolate coordination polymers

Two different 3D coordination polymers, [Gd(glc)(Hglc)(H2O)]n·nH2O (1) and [Gd(Hglc)3]n (2) (H2glc = glycolic acid), have been prepared based on the reaction of Gd(III) ions with H2glc in different pH environments. Due to the deprotonation of the α-OH groups from half of the H2glc ligands in 1, [Gd2] units with a Gd–O–Gd bridging model are observed and suggest a stronger magnetic coupling than that in 2. Magnetic and heat capacity studies reveal the significant impact of the strength of magnetic coupling on the magneto-caloric effect (MCE) in systems. Although a theoretical calculation suggests the −ΔSm (50.5 J kg−1 K−1) of 1 is larger than 2 (45.2 J kg−1 K−1), the stronger antiferromagnetic coupling in 1 decreases the number of low-lying excited spin states upon the lowering of temperature, thus giving a smaller value of −ΔSm than 2 at various fields (e.g. −ΔSm,max = 24.8 J kg−1 K−1 and 41.1 J kg−1 K−1 for 1 and 2 respectively at ΔH = 3 T). This case reveals that the effect of magnetic coupling on MCE plays a dominant role for designing low-temperature 3D Gd(III)-based magnetic coolants.

Unprecedented hexagonal bipyramidal single-ion magnets based on metallacrowns

Two Ln(iii) (Ln = Ce or Nd) complexes based on [15-MC-6] (MC = metallacrown) and phosphine oxide are reported for the first time with the Ln(iii) ion featuring nearly perfect hexagonal bipyramidal LnO8 geometry, with pseudo-D6h symmetry. Magnetic measurements reveal that both behave as single-ion magnets (SIMs), where the slow relaxation is dominated by the Raman mechanism.

Spin-Crossover Phenomenon in a Pentanuclear Iron(II) Cluster Helicate

The first spin-crossover cluster helicate [{Fe(II)(μ-bpt)3}2Fe(II)3(μ3-O)][Fe(II)2(μ-Cl)(μ-bpt)(NCS)4(H2O)]·2H2O·C2H5OH [Hbpt = 3,5-bis(pyridin-2-yl)-1,2,4-triazole] was reported, in which one spin-crossover unit and one low-spin triple-stranded [Fe(II)(bpt)3](-) unit wrapped a rare planar [Fe(II)3(μ3-O)](4+) core to form a bis(triple-helical) cation with trigonal-bipyramidal topology. The origin of different magnetic behaviors of two [Fe(II)(bpt)3](-) units could be ascribed to their different intermolecular interactions.

A Piezochromic Dysprosium(III) Single-Molecule Magnet Based on an Aggregation-Induced-Emission-Active Tetraphenylethene Derivative Ligand

A bifunctional dysprosium(III) dimer, [Dy2(HTPEIPOMe)2(OAc)4(NO3)2] (1), comprising an AIE-active (AIE = aggregation-induced emission) ligand of 2-methoxy-6-[[[4-(1,2,2-triphenylvinyl)phenyl]imino]methyl]phenol (HTPEIPOMe), was successfully synthesized. It not only behaves as a single-molecule magnet (SMM) with an energy barrier of 168(15) K at zero field but also exhibits piezochromism during the pressing-fuming cycle with switchable color, photoluminescence, and magnetic response.

Evolution of Slow Magnetic Relaxation: from Diamagnetic Matrix Y(OH)CO3 to Dy0.06Y0.94(OH)CO3 with High Spin-Reversal Barrier and Blocking Temperature

A stable Dy(III)-dispersed compound with single-molecule magnet behavior, Dy(0.06)Y(0.94)(OH)CO3, was isolated by a general strategy targeted at the doping of paramagnetic Dy(3+) into a diamagnetic 3D inorganic network of Y(OH)CO3. The single-ion origin of slow magnetic relaxation was gradually released as variations of the dysprosium/yttrium ratio and finally gave a relatively large spin-reversal barrier around 200 K and high hysteresis temperature of 8 K. This study opens up new opportunities to investigate the slow magnetic relaxation and magnetostructural correlation by choosing a suitable inorganic architecture with strong axial anisotropy.

[2 + 2] Photochemical modulation of the Dy(III) single-molecule magnet: opposite influence on the energy barrier and relaxation time

The photochemical [2 + 2] reaction between two coordinated bpe (bpe = 1,2-bis(4-pyridyl)ethene) ligands in a new Dy(III)-based single-molecule magnet (SMM) was successfully performed. Under UV irradiation, each pair of coordinated bpe ligands from two adjacent cationic motifs in the complex (Hbpe)2[Dy(bpe)(H2O)(4-pyO)(NO3)(SCN)3]SCN (1) successfully underwent a complete [2 + 2] dimerization, leading to a dimeric cyclobutyl product, (Hbpe)2(H2tpcb)[Dy2(tpcb)2(H2O)2(4-pyO)2(NO3)2(SCN)6](SCN)2 (2, tpcb = tetrakis(4-pyridyl)cyclobutane, 4-pyO = 4-(1H)-pyridone), through single-crystal-to-single-crystal (SCSC) transformation. As revealed by alternating-current (ac) susceptibility measurements, the subtle changes of the coordination environment around Dy(III) ions result in the enhancement of the effective energy barrier from 1 (Ueff = 153.8 K and 201.9 K under zero and 1500 Oe dc field respectively) to 2 (Ueff = 205.5 K and 234.5 K under zero and 1500 Oe dc field respectively). Oppositely, the magnetic relaxation time at low temperatures under the field of 1500 Oe is obviously shortened after irradiation due to the variation of the dominant Raman process.

Construction of lanthanide single-molecule magnets with the “magnetic motif” [Dy(MQ)4]−

A dinuclear complex (HNEt3)[Dy2(MQ)4(NO3)3]·EtOH·H2O (HMQ = 2-methyl-8-hydroxyquinoline) was prepared and proved to have no observable single-molecule magnet (SMM) behaviour. With increasing NEt3 in the reaction, two coordinated NO3− units in the {(NO3)3} pocket were replaced by an additional “magnetic motif” [Dy(MQ)4]−. In this way, the unfavourable interactions between the two dysprosiums were diminished and a trinuclear complex [Dy3(MQ)8(NO3)] was obtained, which behaves as an SMM with an efficient energy barrier of 244(21) K for the full temperature range and 150(12) K for the high-temperature region. It is suggested that introduction of a “magnetic motif” is a feasible strategy for modulating the magnetic behaviour of polynuclear systems.