Close-packed nitronyl nitroxide radicals by Au-S self-assembly: strong ferromagnetic coupling

The study of the magnetism of tightly arranged nitronyl nitroxide (NN) radicals via Au-S self-assembly is interesting. In this study, a series of radicals (S-NN, D-NN, BS-NN, BD-NN) along with two types of nanomaterials (S-NPs, D-NPs) were synthesized. NN was chosen for the magnetic units. Their structures have been successfully synthesized and analyzed. The spin magnetic properties were characterized by electron paramagnetic resonance (EPR) and superconducting quantum interference device (SQUID) measurement. The analysis revealed that the self-assembled NN formed via Au-S bonds exhibits high packing density. Furthermore, it was gratifying to observe that the AuNPs exhibit ferromagnetism after the surface modification by NN. This results in strong ferromagnetic exchange interactions of S-NPs and D-NPs : J S-NPs = +279.715 K and J D-NPs = +254.913 K, respectively.

Effect of the heteroatom on the magnetic and luminescence properties of hybrid lanthanide-substituted Keggin-type polyoxometalates

Replacement of the heteroatom from Si to Ge has a strong influence on the luminescence properties of a series of hybrid, sandwich-type K5[Ln(α-GeW11O39)(C20H22Br2N2O4)]·14H2O (1Ge-Ln, Ln = Sm to Lu) anions. Interestingly, the Gd and Yb derivatives retain their ability to display slow relaxation of magnetisation.

Slow magnetic relaxation of a S = 1/2 copper(II)-substituted Keggin-type silicotungstate

This is the first report on slow magnetic relaxation in an S = 1/2 system based on a first-row transition metal ion with the polyoxometalate skeleton [(n-C₄H₉)₄N]₄H₂[SiW₁₁O₃₉Cu] (1). The X-band electron-spin-resonance spectrum of 1 measured at room temperature indicates that the copper ion experiences significantly reduced intermolecular interactions compared to the potassium salt and that it adopts a five-coordinated square-pyramidal coordination geometry. The AC magnetic-susceptibility measurements revealed that 1 undergoes slow magnetic relaxation in an applied static magnetic field (H_dc). The extracted spin-lattice relaxation time (92 ms at 1.8 K and H_dc = 5000 Oe) for 5% magnetically diluted 1, [(n-C₄H₉)₄N]₄H₂[SiW₁₁O₃₉Cu_0.05Zn_0.95] (dil.1), is comparable to those of other potential S = 1/2 spin qubits. A relaxation-time analysis indicated that Raman spin-lattice relaxation dominates even at low temperatures in an optimized field. The extracted Raman exponent (n = 2.30) is smaller than those of other S = 1/2 complexes that carry organic ligands, which implies that the decrease in relaxation time at higher temperatures is likely to be moderate.

Fluoride-bridged dinuclear dysprosium complex showing single-molecule magnetic behavior: supramolecular approach to isolate magnetic molecules

Using Na-encapsulated benzo[18]crown-6 (Na)(B18C6) as a counter cation, we successfully magnetically isolated a fluoride-bridging Dy dinuclear complex {[(PW11O39)Dy(H2O)2]2F} (Dy2POM) with lacunary Keggin ligands. (Na)(B18C6) formed two types of tetramers through C-H⋯O, π⋯π and C-H⋯π interactions, and each tetramer aligned in one dimension along the c-axis to form two types of channels. One channel was partially penetrated by a supramolecular cation from the ±a-axis direction, dividing the channel in the form of a "bamboo node". Dy2POM was spatially divided by this "bamboo node," which magnetically isolated one portion from the other. The temperature dependence of the magnetic susceptibility indicated a weak ferromagnetic interaction between the Dy ions bridged by fluoride. Dy2POM exhibited the magnetic relaxation characteristics of a single-molecule magnet, including the dependence of AC magnetic susceptibility on temperature and frequency. Magnetic relaxation can be described by the combination of thermally active Orbach and temperature-independent quantum tunneling processes. The application of a static magnetic field effectively suppressed the relaxation due to quantum tunneling.

Slow Magnetic Relaxation and Luminescent Properties of Mononuclear Lanthanide-Substituted Keggin-Type Polyoxotungstates with Compartmental Organic Ligands

The reaction of mid to late lanthanide ions with the N,N′-dimethyl-N,N′-bis(2-hydroxy-3-formyl-5-bromobenzyl)ethylene-diamine organic ligand and monolacunary Keggin type [α-SiW₁₁O₃₉]^8– anion affords a series of isostructural compounds, namely, K₅[Ln^III(α-SiW₁₁O₃₉)(C₂₀H₂₂Br₂N₂O₄)]·14H₂O (1-Ln, Ln = Sm to Lu). The molecular structure of these sandwich-type complexes is formed by the Ln^III ion in a biaugmented trigonal prismatic geometry, which occupies the external O₄ site of the organic ligand and the vacant site of the lacunary polyoxometalate (POM) unit. The empty N₂O₂ coordination site of the organic ligand allows its unprecedented folding, which displays a relative perpendicular arrangement of aromatic groups. Weak Br···Br and π–π interactions established between adjacent molecular units govern the crystal packing, which results in the formation of assemblies containing six hybrid species assembled in a chairlike conformation. 1-Gd and 1-Yb display slow relaxation of the magnetization after the application of an external magnetic field with maxima in the out-of-phase magnetic susceptibility plots below ∼5–6 K, which is ascribed to the presence of various relaxation mechanisms. Moreover, photoluminescent emission is sensitized for 1-Sm and 1-Eu in the visible region and 1-Er and 1-Yb in the NIR. In contrast, the quenching of metal-centered luminescence in the 1-Tb derivative has been attributed to the out-of-pocket coordination mode of the lanthanide center within the POM fragment. It is demonstrated that the 1-Yb dual magneto-luminescent material represents the first lanthanide-containing POM reported to date with simultaneous slow magnetic relaxation and NIR emission. Solution stability of the hybrid molecular species in water is also confirmed by ESI-mass spectrometry experiments carried out for 1-Tb and 1-Tm.

A series of solution stable, molecular polyoxometalate hybrids, namely, [α-SiW₁₁O₃₉Ln^III(C₂₀H₂₂N₂Br₂O₄)]⁵⁻ (Ln^III = Sm to Lu) have been synthesized from the combination of mid-to-late lanthanides, lacunary Keggin-type anions, and a compartmental organic ligand. Metal-centered luminescence in both the visible and NIR region as well as slow relaxation of magnetization was found for different members of this family, including the Yb derivative, which represents the first POM-based system with slow magnetic relaxation and sensitized emission in the NIR region.

Hybrid lanthanide double-deckers based on calixarene and polyoxometalate units

Complementarity of calixarene (H2L) and polyoxometalate ligands results in the first organic-inorganic [M(III)L{Mo5O13(OMe)4(NO)}]2– (M = Y, Gd and Dy) hybrid, directing the formation of a distorted square-antiprismatic MO8 ligand field,...

A magnetic site dilution approach to achieve bifunctional fluorescent thermometers and single-ion magnets

In complex [Na-Dy(μ₂-L)₄]_n(HL = 8-hydroxyquinoline) (1), the DyL₄ units were linked by the Na^I ions to form one-dimensional chains. The chain exhibited slow magnetic relaxation behavior at low temperature, accompanied by obvious quantum tunneling of magnetization (QTM). Very weak fluorescence was detected in 1 due to the mismatch of the state energy between Dy^III and the L ligand. Through the magnetic dilution of diamagnetic Y^III ions, complex [NaDy_0.02Y_0.98(μ₂-L)₄]_n (2) was obtained; in 2 the QTM of Dy^III was suppressed and the single ion magnet (SIM) behavior was enhanced. More interestingly, the fluorescence emission of 8-hydroxyquinoline was lightened by the Y^III ions in 2, whose intensity is linearly correlated with the temperature variation. The examples of dual functional fluorescent thermometers and SIM materials are attained simply by ion dilution, achieving the effect of killing two birds with one stone.

A systematic study of the optical properties of mononuclear hybrid organo–inorganic lanthanoid complexes

Mononuclear organic–inorganic hybrid lanthanoid complexes show that the combination of both types of ligands improves the optical response compared to the inorganic analogue, thus having potential optical applications due to their thermal response.