Cryogenic magnetocaloric effect in a ferromagnetic molecular dimer

A Cubic Tinkertoy-like Heterometallic Cluster with a Record Magnetocaloric Effect

Clusters showing a giant magnetocaloric effect (MCE) are of interest as molecular coolants for magnetic refrigeration. Herein, we report two heterometallic clusters, denoted as Gd152Ni14@Cl24 and Sm152Ni8, just to highlight their inorganic core motifs, obtained by ligand-controlled co-hydrolysis of Ni2+ and Ln3+ (Ln = Gd, Sm) in the presence of N-(2-hydroxyethyl)iminodiacetic acid (H2HEIDA). Both clusters display fascinating cubic Tinkertoy-like structures, with the core motifs being built of multiple metallic shells of Platonic and Archimedean polyhedra. The isothermal magnetic entropy change─a direct measurement of MCE─was determined to be 52.65 J·kg-1·K-1 at 2.5 K and 7.0 T for the Gd-containing cluster; this value is the highest known for any molecular clusters so far reported.

Exceptional Magnetocaloric Responses in a Gadolinium Silicate with Strongly Correlated Spin Disorder for Sub-Kelvin Magnetic Cooling

The development of magnetocaloric materials with a significantly enhanced volumetric cooling capability is highly desirable for the application of adiabatic demagnetization refrigerators in confined spatial environments. Here, the thermodynamic characteristics of a magnetically frustrated spin-7/2 Gd9.33[SiO4]6O2 is presented, which exhibits strongly correlated spin disorder below ≈1.5 K. A quantitative model is proposed to describe the magnetization results by incorporating nearest-neighbor Heisenberg antiferromagnetic and dipolar interactions. Remarkably, the recorded magnetocaloric responses are unprecedentedly large and applicable below 1.0 K. It is proposed that the S = 7/2 spin liquids serve as versatile platforms for investigating high-performance magnetocaloric materials in the sub-kelvin regime, particularly those exhibiting a superior cooling power per unit volume.

Synthesis, structures and magnetic studies of hexanuclear lanthanide complexes: SMM behavior of the DyIII analogue and MCE properties of the GdIII analogue

The synthesis, structure and magnetic properties of homometallic hexanuclear lanthanide complexes [Ln6(HL)4(tfa)4(S)2]·2NO3·x H2O·yMeOH (1, Ln = Gd, S = MeOH, x = 0, y = 0; 2, Ln = Tb, S = H2O, x = 2, y = 2; 3, Ln = Dy, S = MeOH, x = 0, y = 2; 4, Ln = Er, S = MeOH, x = 0, y = 2). [(H4L) = 6-((bis(2-hydroxyethyl)amino)-N'-(2-hydroxybenzylidene)picolinohydrazide) (tfa = trifloroacetylacetone)] are reported. These hexanuclear assemblies are made up of two trinuclear triangular sub-units linked through the oxygen atoms of two phenoxide bridging groups in a corner sharing arrangement. Magnetic studies reveal that 1 displays a magnetocaloric effect with a maximum value of -ΔSm = 21.03 J kg-1 K-1 at T = 3 K and under an applied field change ΔB = 5 T. Complex 3 shows slow relaxation of magnetization even under zero applied field although a clear maximum in the ac susceptibility plots cannot be seen. However, under an optimal applied field of 0.2 T, clear maxima are observed in the out-of-phase (χ''M) component of the ac susceptibility in the temperature range 3.5 K (2 kHz) to 10.5 K (10 kHz). The temperature dependence of the relaxation times could be fitted to the sum of Orbach, Raman and QTM relaxation processes affording the following parameters: τo = 3.4(9) × 10-8 s, Ueff = 94(2) K, BRaman = 16.43(1) K-n s-1, n = 3.2(3) and τQTM = 0.0044(3) s. 4, under an applied magnetic field of 0.2 T, shows slow relaxation of magnetization through a thermally activated Orbach process with Ueff = 18.2(9) K and τo = 3.5(3) × 10-8 s.

Giant and highly anisotropic magnetocaloric effects in single crystals of disordered-perovskite RCr0.5Fe0.5O3 (R = Gd, Er)

Magnetic anisotropy is crucial in examining suitable materials for magnetic functionalities because it affects their magnetic characteristics. In this study, disordered-perovskite RCr_0.5Fe_0.5O₃ (R = Gd, Er) single crystals were synthesized and the influence of magnetic anisotropy and additional ordering of rare-earth moments on cryogenic magnetocaloric properties was investigated. Both GdCr_0.5Fe_0.5O₃ (GCFO) and ErCr_0.5Fe_0.5O₃ (ECFO) crystallize in an orthorhombic Pbnm structure with randomly distributed Cr³⁺ and Fe³⁺ ions. In GCFO, the long-range order of Gd³⁺ moments emerges at a temperature of T_Gd (the ordering temperature of Gd³⁺ moments) = 12 K. The relatively isotropic nature of large Gd³⁺ moment originating from zero orbital angular momentum exhibits giant and virtually isotropic magnetocaloric effect (MCE), with a maximum magnetic entropy change of [Formula: see text] ≈ 50.0 J/kg·K. In ECFO, the highly anisotropic magnetizations result in a large rotating MCE characterized by a rotating magnetic entropy change [Formula: see text] = 20.8 J/kg·K. These results indicate that a detailed understanding of magnetically anisotropic characteristics is the key for exploring improved functional properties in disordered perovskite oxides.

Three Gd-based magnetic refrigerant materials with high magnetic entropy: From di-nuclearity to hexa-nuclearity to octa-nuclearity

Magnetocaloric effect (MCE) is one of the most promising features of molecular-based magnetic materials. We reported three Gd-based magnetic refrigerant materials, namely, Gd₂(L)(NO₃)(H₂O)‧CH₃CN‧H₂O (1, H₂L = (Z)-N-[(1E)-(2-hydroxy-3-methphenyl)methylidene]pyrazine-2-carbohydrazonic acid), {Gd₆(L)₆(CO₃)₂(CH₃OH)₂(H₂O)₃Cl}Cl‧4CH₃CN (2), and Gd₈(L)₈(CO₃)₄(H₂O)₈‧2H₂O (3). Complex 1 contains two Gd^III ions linked by two η²:η¹:η¹:η¹:μ₂-L^2- ligands, which are seven-coordinated in a capped trigonal prism, and complex 2 possesses six Gd^III ions, contributing to a triangular prism configuration. For complex 3, eight Gd^III ions form a distorted cube arrangement. Moreover, the large values of magnetic entropy in the three complexes prove to be excellent candidates as cryogenic magnetic coolants.

Magnetic cooling: a molecular perspective

The magnetocaloriceffect is considered as an energy-efficient and environmentally friendly technique which can take cooling technology to the next level. Apart from its commercial application at room temperature, magnetic refrigeration is an up-and-coming solution for the cryogenic regime, especially as an alternative to He³ systems. Molecular magnets reveal advantageous features for ultra-low cooling which are competitive with intermetallic and lanthanide alloys. Here, we present a guide to the current status of magnetocaloric effect research of molecular magnets with a theoretical background focused on the inverse magnetocaloric effect and an overview of recent results and developments, including the rotating magnetocaloric effect.

Magnetocaloric Effect of Two Gd-Based Frameworks

Magnetic refrigeration material is the key to adiabatic demagnetization refrigeration technology. In this work, two magnetic refrigerants, Gd5(C4O4)(HCOO)3(CO3)2(OH)6·2.5H2O (1) and Gd2(OH)4SO4 (2), were prepared through hydrothermal reaction. Magnetic study reveals that their magnetic entropy changes are 24.8 J kg−1 K−1 for 1 and 15.1 J kg−1 K−1 for 2 at 2 K and 2 T, respectively. The magnetic entropy changes of 1 and 2 at T = 2 K and ∆H = 2 T exceed most gadolinium hydroxyl compounds, indicating that magnetic refrigerants with large magnetic entropy changes at low magnetic fields can be obtained by introducing more weak magnetic exchange ligands to replace hydroxyl groups in gadolinium hydroxyl compounds.

Heterometallic Hexanuclear [Cu2 Ln4 ] Complexes Showing Zero-field SMM Behaviour and Magnetocaloric Effect

Three heterometallic hexanuclear 3d-4f complexes bearing the formula [Cu₂ (L)₂ Ln₄ (L)₄ (o-van)₂ ] [L=2-((E)-((2-hydroxyphenyl)imino]methyl)phenol; o-van=ortho-vanillin] (Ln^III =Gd^III (1), Dy^III (2), and Tb^III (3)) have been synthesized and characterized. DC magnetic susceptibility measurements reveal overall antiferromagnetic interactions in 1 and 3, whereas co-existence of ferro- as well as antiferromagnetic interactions were observed in 2. The magnetocaloric effect has been observed for 1 with an entropy change (-ΔS_m ) of 22.3 J kg^-1  K^-1 at 3 K and 7 T. Zero-field single molecule magnet (SMM) behaviour has been observed for 2, where Raman relaxation and quantum tunneling of magnetization (QTM) played a role in magnetization relaxation. The Cu-O-Ln angle well explains the magnetic exchange coupling occurring in the complexes. BS-DFT calculation for the complexes provides an estimate of the exchange interactions between the paramagnetic centres. Ab initio calculations performed for complex 2 established a good correlation to the experimental relaxation dynamics.

Oxidation of europium with ammonium perfluorocarboxylates in liquid ammonia: pathways to europium(II) carboxylates and hexanuclear europium(III) fluoridocarboxylate complexes

The novel coordination polymer [Eu(O₂CCF₃)₂(dmf)₂]_∞ (1) (dmf = N,N-dimethylformamide) containing europium(II) and the two new compounds (NH₄)₂[Eu₆F₈(O₂CCF₃)₁₂(CF₃COOH)₆] (2) and (NH₄)₂[Eu₆F₈(O₂CC₂F₅)₁₂(C₂F₅COOH)₆]·8C₂F₅COOH (3), both based on hexanuclear europiate(III) complexes, were synthesized from precursors with a Eu²⁺ : Eu³⁺ ratio >1, obtained by reaction of europium metal with ammonium perfluorocarboxylates in liquid ammonia. In the crystal structure of 1 the europium(II) ions are bridged by carboxylate groups and N,N-dimethylformamide to form polymeric chains with Eu²⁺⋯Eu²⁺ distances of 408.39(13)-410.49(13) pm. The compound crystallizes in the triclinic space group P1̄ (Z = 2). To the best of our knowledge, this is the first example of a (solvated) perfluorocarboxylate containing a lanthanoid in a subvalent oxidation state. In the crystal structures of 2 and 3 the europium(III) ions are bridged by fluoride ions and carboxylate groups to form hexanuclear complex anions with an octahedral arrangement of the cations. The Eu³⁺⋯Eu³⁺ distances are in the range of 398.27(15)-400.93(15) pm in 2 and 395.37(4)-399.78(5) pm in 3, respectively. Both compounds crystallize in the monoclinic space group type P2₁/n (Z = 4) and are the first examples of octahedro-hexanuclear europium carboxylates for which fluoride is reported as a bridging ligand. In all compounds the oxidation state of europium was monitored via¹⁵¹Eu Mössbauer and photoluminescene spectroscopy.

Printing Air-Stable High-Tc Molecular Magnet with Tunable Magnetic Interaction

High-T_c molecular magnets have amassed much promise; however, the long-standing obstacle for its practical applications is the inaccessibility of high-temperature molecular magnets showing dynamic and nonvolatile magnetization control. In addition, its functional durability is prone to degradation in oxygen and heat. Here, we introduce a rapid prototyping and stabilizing strategy for high T_c (360 K) molecular magnets with precise spatial control in geometry. The printed molecular magnets are thermally stable up to 400 K and air-stable for over 300 days, a significant improvement in its lifetime and durability. X-ray magnetic circular dichroism and computational modeling reveal the water ligands controlling magnetic exchange interaction of molecular magnets. The molecular magnets also show dynamical and reversible tunability of magnetic exchange interactions, enabling a colossal working temperature window of 86 K (from 258 to 344 K). This study provides a pathway to flexible, lightweight, and durable molecular magnetic devices through additive manufacturing.

Magnetocaloric effect and slow magnetic relaxation in peroxide-assisted tetranuclear lanthanide assemblies

Investigation of a series of rare peroxide-assisted tetranuclear lanthanide assemblies revealed both significant magnetocaloric effect and slow magnetic relaxation.

Wheel-like Gd42 Polynuclear Complex with Significant Magnetocaloric Effect

Two novel wheel-like lanthanide nanoclusters with 42 nuclearity [Ln42L14(OH)28(OAc)84] (abbreviated as Ln42, 1-Gd; 2-Dy, HL=3-methoxysalicylaldehyde O-vanillin) were structurally and magnetically characterized. The Ln42 species were constructed by O-vanillin and lanthanide...

Efficiently increasing low-field magnetic entropy by incorporating SO32− into Gd22Ni21 clusters

One distinct nanosized cluster, Gd22Ni21, was isolated by the mixed-anion-templates (SO32- and SO42-), which was firstly reported in 3d-4f metal clusters. Additionally, Gd22Ni21 shows the largest low-field magnetic entropy change...

Ready Access to Anhydrous Anionic Lanthanide Acetates by Using Imidazolium Acetate Ionic Liquids as the Reaction Medium

Access to lanthanide acetate coordination compounds is challenged by the tendency of lanthanides to coordinate water and the plethora of acetate coordination modes. A straightforward, reproducible synthetic procedure by treating lanthanide chloride hydrates with defined ratios of the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([C2 mim][OAc]) has been developed. This reaction pathway leads to two isostructural crystalline anhydrous coordination complexes, the polymeric [C2 mim]n [{Ln2 (OAc)7 }n ] and the dimeric [C2 mim]2 [Ln2 (OAc)8 ], based on the ion size and the ratio of IL used. A reaction with an IL : Ln-salt ratio of 5 : 1, where Ln=Nd, Sm, and Gd, led exclusively to the polymer, whilst for the heaviest lanthanides (Dy-Lu) the dimer was observed. Reaction with Eu and Tb resulted in a mixture of both polymeric and dimeric forms. When the amount of IL and/or the size of the cation was increased, the reaction led to only the dimeric compound for all the lanthanide series. Crystallographic analyses of the resulting salts revealed three different types of metal-acetate coordination modes where η2 μκ2 is the most represented in both structure types.

Magnetocaloric Effect and Thermal Conductivity of a 3D Coordination Polymer of [Gd(HCOO)(C2O4)]n

A 3D coordination polymer, [Gd(HCOO)(C₂O₄)]_n was prepared. Its magnetocaloric effect (MCE) (32.7 J K^-1 kg^-1 at 2 K and 2 T) is significantly larger than that of commercial Gd₃Ga₅O₁₂ (GGG) (14.6 J kg^-1 K^-1 at 2 K and 2 T), while its thermal conductivity (9.9 W m^-1 K^-1 at 3 K) is comparable to that of the commercial GGG (about 10 W m^-1 K^-1 at 3 K).

Complete mapping of the thermoelectric properties of a single molecule

Theoretical studies suggest that mastering the thermocurrent through single molecules can lead to thermoelectric energy harvesters with unprecedentedly high efficiencies.^1-6 This can be achieved by engineering molecule length,⁷ optimizing the tunnel coupling strength of molecules via chemical anchor groups⁸ or by creating localized states in the backbone with resulting quantum interference features.⁴ Empirical verification of these predictions, however, faces considerable experimental challenges and is still awaited. Here we use a novel measurement protocol that simultaneously probes the conductance and thermocurrent flow as a function of bias voltage and gate voltage. We find that the resulting thermocurrent is strongly asymmetric with respect to the gate voltage, with evidence of molecular excited states in the thermocurrent Coulomb diamond maps. These features can be reproduced by a rate-equation model only if it accounts for both the vibrational coupling and the electronic degeneracies, thus giving direct insight into the interplay of electronic and vibrational degrees of freedom, and the role of spin entropy in single molecules. Overall these results show that thermocurrent measurements can be used as a spectroscopic tool to access molecule-specific quantum transport phenomena.

Magnetic properties of two GdIIIFeIII4 metallacrowns and strategies for optimizing the magnetocaloric effect of this topology

Two Gd³⁺ [12-MC_Fe^III_(N)shi-4] metallacrowns are analyzed for magnetic properties, and calculations concerning the magnetic exchange parameters of this topology are considered.

A free-standing, self-healing multi-stimuli responsive gel showing cryogenic magnetic cooling

A novel Fe(iii)-based gel was synthesized via the self-assembly of Fe(iii) and pyridine 2,6 dicarboxylic acid. The synthesized gel has remarkable mechanical strength as well as self-sustainability. The metallogel also has thixotropic as well as self-healing properties. The metallogel shows amazing colourimetric NH3 sensing with unique gel-to-gel transformation. Magnetic studies on the as-synthesized gel reveal significant cryogenic magnetic cooling behavior. Last but not least, to the best of our knowledge, this would be the first case where MCE is investigated for any reported metallogel.

Low-Temperature Magnetocaloric Properties of V12 Polyoxovanadate Molecular Magnet: A Theoretical Study

The paper presents a computational study of the magnetocaloric properties of the V12 polyoxovanadate molecular magnet. The description is restricted to low-temperature range (below approximately 100 K), where the magnetic properties of the system in question can be sufficiently modelled by considering a tetramer that consists of four vanadium ions with spins S=1/2. The discussion is focused on the magnetocaloric effect in the cryogenic range. The exact and numerical diagonalization of the corresponding Hamiltonian is used in order to construct the thermodynamic description within a version of the canonical ensemble. The thermodynamic quantities of interest, such as magnetic entropy, specific heat, entropy change under isothermal magnetization/demagnetization, temperature change under adiabatic magnetization/demagnetization, refrigerant capacity, and magnetic Grüneisen ratio, are calculated and discussed extensively. The importance of two quantum level crossings for the described properties is emphasized. The significant ranges of direct and inverse magnetocaloric effect are predicted. In particular, the maximized inverse magnetocaloric response is found for cryogenic temperatures.

Gadolinium-Rich Borate Gd17.33(BO3)4(B2O5)2O16 Exhibiting a Magnetocaloric Effect

A gadolinium-rich borate Gd_17.33(BO₃)₄(B₂O₅)₂O₁₆ was successfully grown by the high-temperature solution method using the Rb₂O-B₂O₃ flux. The crystal crystallizes in centrosymmetric space group C2/m with lattice constants a = 18.4300(2) Å, b = 3.7400(4) Å, c = 14.2047(16) Å, and β = 119.8550(12)°. Two different honeycomb-like [GdO] layers alternately arrange in the order ABAB forming the three-dimensional framework, in which the isolated [B₂O₅] and [BO₃] units fill in channels of the 12-membered and 10-membered [GdO] polyhedral rings, respectively. The UV cutoff edge of Gd_17.33(BO₃)₄(B₂O₅)₂O₁₆ is less than 240 nm. The maximum -ΔS_m,max is 26.53 J kg^-1 K^-1 or 174.70 mJ cm^-3 K^-1 (T = 4.4 K and ΔH = 7 T) as investigated by the isothermal magnetization method.

Heterometallic 3d–4f {Co2Gd4} phosphonates: new members of the potential magnetic cooler family

Three new 3d–4f heterometallic phosphonate complexes with the formula [Na₂CoIII2Gd₄(L)₆(bpy)₂(OR)₂]·nSolv (L = SAA³⁻(1), BSAA³⁻(2), and NAA³⁻(3); bpy = 2,2′-bipyridine; OR = OH and OMe; Solv = H₂O and MeOH) were isolated and studied in detail.

Two [Ln4] molecular rings folded as compact tetrahedra

A new highly photo-switchable ligand furnishes supramolecular tetrahedral nanomagnets with Ln(iii) ions (Ln = Dy, Tb). Intramolecular weak interactions define the conformation of the ligand, quenching the photochromic activity.

Syntheses, structures and magnetic properties of novel tetrameric Ln2Mn2 and ring-like Ln4Mn4 clusters

Two series of heterometallic Ln–Mn clusters Ln2Mn2 and Ln4Mn4 were successfully synthesized in the presence of alcohol ligands, and the magnetic coupling interaction between metal ions were characterized by theoretical calculations.

SMM behaviour of heterometallic dinuclear CuIILnIII (Ln = Tb and Dy) complexes derived from N2O3 donor unsymmetrical ligands

Four heterometallic dinuclear Cu^IILn^III (Ln = Tb and Dy) complexes derived from two different N₂O₃ donor unsymmetrical Schiff base ligands exhibit SMM behaviour.

A lanthanide(iii) dodecanuclear structure with a acylhydrazone Schiff-base ligand: slow magnetic relaxation and magnetocaloric effects

In the complex synthesis process, the design of new type structures of lanthanide clusters with high nuclearity provides an opportunity to understand the nature of magnetic dynamics.

Chain caesium borophosphates with B:P ratio 1:2: synthesis, structure relationships and low-temperature thermodynamic properties

Three caesium-bearing borophosphates, Cs[BP₂O₆(OH)₂] (I), Cs_0.51Mn_1.17(H₂O)₂[BP₂O₈]·0.45H₂O (II) and CsMn[BP₂O₈(OH)] (III), were synthesized by a hydrothermal method at 473-523 K. Their crystal structures have been studied by means of single-crystal X-ray diffraction; all three structures comprise borophosphate chain anions with a B:P ratio of 1:2. The unique construction of (I) is based on four-membered-ring chains running parallel to the [010] direction. These protonated borophosphate chains are linked via hydrogen-bond interactions to form a 3D framework with caesium cations incorporated. (II) is the first Cs and Mn²⁺,Mn³⁺ member of a known family characterized by [BP₂O₈]_∞ helical chains running along [001]. These chains are connected through MnO₄(H₂O)₂ octahedra to form a 3D framework. The caesium cations are disordered over two independent positions in the channels, which they occupy together with water molecules. An additional MnO₂(H₂O)₃ bipyramid statistically shares a common edge and two corners with three main Mn octahedra to form tetrameric clusters. The topological relation between the chain anionic fragments of (I) and (II) as well as the structural relation between (I) and previously studied boro- and berillophosphates are discussed. Compound (III) presents the first Mn member of the A^IM^III[BP₂O₈(OH)] family and is characterized by a 3D framework built by open-branched borophosphate chains and MnO₅ semi-octahedra sharing vertices. The measurements of thermodynamic properties, i.e. magnetization M and specific heat C_p, to 2 K and 30 T, provide evidence that (II) orders antiferromagnetically at the Néel temperature T_N = 4.6 K and exhibits a plateau-like feature under the action of an external magnetic field accompanied by a pronounced magnetocaloric effect.

Magnetic Behavior of Luminescent Dinuclear Dysprosium and Terbium Complexes Derived from Phenoxyacetic Acid and 2,2’-Bipyridine

Two dinuclear lanthanide complexes [Dy2(L1)6(L2)2]·2EtOH (1) and [Tb2(L1)6(L2)2]·2EtOH (2) (HL1 = phenoxyacetic acid and L2 = 2,2’-bipyridine) were synthesized and the crystal structures were determined. In both complexes, the lanthanide centers are nine-coordinated and have a muffin geometry. Detailed magnetic study reveals the presence of field-induced single molecule magnet (SMM) behavior for complex 1, whereas complex 2 is non-SMM in nature. Further magnetic study with 1’, yttrium doped magnetically diluted sample of 1, disclosed the presence of Orbach and Raman relaxation processes with effective energy barrier, ∆E = 16.26 cm−1 and relaxation time, τo = 2.42 × 10−8 s. Luminescence spectra for complexes 1 and 2 in acetonitrile were studied which show characteristic emission peaks for DyIII and TbIII ions, respectively.

The Multiple Faces, and Phases, of Magnetic Anisotropy

The notion of magnetic anisotropy is very central to the field of molecule-based magnetism, where it is considered to be a key quantity that must be rationalized and controlled in order to improve the performances of, e.g., single-molecule magnets. A rough classification of the magnetic properties is widely done in terms of the qualitative descriptors of magnetic anisotropy: "easy-axis" and "easy-plane". They can be based on different physical properties, in casu: free energy, magnetization, or magnetic susceptibility. However, this degree of freedom leads in some cases, including very simple ones like [V(H₂O)₆]³⁺, to incommensurate descriptions of a system being simultaneously easy-axis and easy-plane, depending only on the choice of the physical quantity on which the descriptor is based. Moreover, it has recently been pointed out that the magnetic anisotropy of a chemical system can be addressed and switched using external stimuli like temperature and magnetic field. These external parameters are, though, not the only ones capable of triggering anisotropy switching for actual chemical systems under experimentally relevant conditions. Indeed, this applies also to pressure, as discussed here. In this paper, we try to illustrate the multifaceted nature of magnetic anisotropy and assist the overview using anisotropy phase diagrams.

Europium and ytterbium complexes with o-iminoquinonato ligands: synthesis, structure, and magnetic behavior

Complexes of divalent ytterbium (1) and europium (2) with a dianionic o-amidophenolate ligand were prepared by both the direct reduction of 4,6-di-tert-butyl-N-(2,6-diisopropylphenyl)-o-iminobenzoquinone (dpp-IQ) and the salt metathesis reaction of potassium o-amidophenolate with LnI2 (Ln = Yb, Eu). Oxidation of o-amidophenolates 1, 2 with one equivalent of dpp-IQ as well as the salt metathesis reaction of potassium o-iminosemiquinolate with LnI2 afforded ligand mixed-valent o-iminosemiquinonato-amidophenolato complexes of trivalent ytterbium (3) and europium (4). All novel complexes 1-4 were fully characterized, including the solid state structures of 1 and 2 determined by single crystal X-ray diffraction. The magnetic properties of paramagnetic 2-4 were examined.

A new family of dinuclear lanthanide complexes constructed from an 8-hydroxyquinoline Schiff base and β-diketone: magnetic properties and near-infrared luminescence

Six phenoxo-O bridged dinuclear lanthanide(iii) complexes have been assembled utilizing the 2-[(4-nitrophenyl)imino]methyl-8-hydroxyquinoline (HL) and dibenzoylmethane (Hdbm) ligands: [Ln2(dbm)4L2] (Ln = Nd (1), Eu (2), Gd (3), Tb (4), Dy (5) and Er (6)). Complexes 1 and 6 exhibit the characteristic emission peaks of the corresponding Nd3+ and Er3+ ions, respectively. Meanwhile, the excitation wavelength (470 nm) for complex 1 is located in the visible-light region, confirming a practical application value. The studies on magnetic properties reveal that complex 3 features a magnetocaloric effect with a magnetic entropy change of -ΔSm = 14.36 J kg-1 K-1 at 4 K for ΔH = 7 T. What's more, the dynamic magnetic studies for complex 5 show that it exhibits slow magnetic relaxation behavior, typical of SMM behavior, resulting in an energy barrier of ΔE/kB = 75 K with the pre-exponential factor τ0 = 2.2 × 10-7 s. Meanwhile, this research demonstrates that the magnetic properties can be modulated by regulating the electron-donating/withdrawing effects of the substituents on the ligands.