MnII-GdIII Phosphonate Cages with a Large Magnetocaloric Effect

Identification of seven-coordinate LnIII ions in a LnIII[15-MCFe III N(shi)-5](OAc)2Cl species crystallized from methanol and pyridine

The title metallacrown (MC) complexes LnIII[15-MCFeIIIN(shi)-5](OAc)2CI(C5H5N)6 (Ln1), where OAc- is acetate, shi3- is salicylhydroximate, and Ln = Gd and Dy, were synthesized via a self-assembly reaction in methanol and pyridine. Single crystals were grown using slow evaporation and characterized using X-ray diffraction. Seven-coordinate capped octahedron geometries were observed for the lanthanide ion in both complexes, which is uncommon for trivalent lanthanide species. The 15-MC-5 is a ruffled metallacrown archetype similar to previously reported mixed-valent manganese metallacrowns.

Two SiO44--Templated Ln23Ni20 Clusters with Magnetic Cooling and Stability

Assembling and studying high-nuclearity 3d-4f metal clusters represent a pregnant and challenging research hotspot. Based on anionic template and ligand-controlled hydrolytic methods, two heterometallic metal clusters, formulated as [Gd₂₃Ni₂₀(DTA)₂₀(CO₃)₄(CH₃COO)₆(SiO₄)₄(CH₃CH₂OH)₂(μ₃-OH)₃₃(μ₂-OH)₄(H₂O)₁₆]·Cl₂·30H₂O and [Eu₂₃Ni₂₀(DTA)₂₀(CO₃)₄(CH₃COO)₆(SiO₄)₄(CH₃CH₂OH)₂(μ₃-OH)₃₃(μ₂-OH)₄(H₂O)₁₆]·Cl₂·46H₂O (abbreviated as Gd₂₃Ni₂₀, Eu₂₃Ni₂₀, H₂DTA = thiodiglycolic acid), are successfully obtained, which both feature similar double-shell-shaped structures with a Ni₂₀ building unit encapsulating a Ln₂₃ aggregation. The structural analysis illustrates that the SiO₄^4- anion, serving as the anionic template in this work, is reported for the second time in 3d-4f metal clusters. In terms of the magnetic properties, large amounts of Gd³⁺ and Ni²⁺ ions contribute to the MCE of compound Gd₂₃Ni₂₀, along with 38.15 J kg^-1 K^-1 at ΔH = 7.0 T for 2.0 K. It is worth mentioning that compound Gd₂₃Ni₂₀ exhibits an excellent magnetic entropy change at low fields (-ΔS_m = 19.10 J kg^-1 K^-1 at 2.0 K for ΔH = 2.0 T). In addition, Gd₂₃Ni₂₀ exhibits preferable solvent and thermal stability.

Co3Gd4 Cage as Magnetic Refrigerant and Co3Dy3 Cage Showing Slow Relaxation of Magnetisation

Two structurally dissimilar 3d-4f cages having the formulae [(Co^III)₃Gd₄(μ₃-OH)₂(CO₃) (O₂C^tBu)₁₁(teaH)₃]·5H₂O (1) and [(Co^III)₃Dy₃(μ₃-OH)₄(O₂C^tBu)₆(teaH)₃]·(NO₃)₂·H₂O (2) have been isolated under similar reaction conditions and stoichiometry of the reactants. The most important factor for structural diversity seems to be the incorporation of one μ₃-carbonate anion in 1 and not in 2. Co atoms are in a +3 oxidation state in both complexes, as shown by the Bond Valence Sum (BVS) calculations and bond lengths, and as further supported by magnetic measurements. Co₃Gd₄ displays a significant magnetocaloric effect (−∆S_m = 25.67 J kg⁻¹ K⁻¹), and Co₃Dy₃ shows a single molecule magnet (SMM) behavior.

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...

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.

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.

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.

Enhancement of magnetic relaxation properties with 3d diamagnetic cations in [ZnIILnIII] and [NiIILnIII], LnIII= Kramers lanthanides

Comparison between two series of [Ni^IILn^III] and [Zn^IILn^III] dimers reveals lower intermolecular interactions for the square-planar Ni^IIderivatives that favour an induced SIM response. Some unusual Ce^III, Nd^IIIand Yb^IIISIMs are reported.

Zinc-diphosphonates with extended dipyridine units: synthesis, structures, in situ reactions, and photochromism

We report two zinc-diphosphonates bearing extended dipyridine units. In situ reactions and photochromism are observable in the title compounds.

Syntheses, crystal-solution structures and magnetic properties of a series of decanuclear heterometallic [LnCoCo] (Ln = Eu, Gd, Tb, Dy) clusters

Four unprecedented decanuclear heterometallic [Ln2CoII4CoIII4] clusters based on a diethanolamine ligand (H2dea), namely [Eu2CoII4CoIII4(dea)8(HCOO)4(OH)2(Cl)2(CH3OH)2]Cl2·4CH3OH·2H2O (1), [Gd2CoII4CoIII4(dea)8(HCOO)4(OH)2(Cl)2(CH3OH)2]Cl2·4CH3OH·2H2O (2), [Tb2CoII4CoIII4(dea)8(HCOO)4(OH)2(Cl)2(CH3OH)2]Cl2·2CH3OH·4H2O (3) and [Dy2CoII4CoIII4(dea)8(HCOO)4(OH)2(Cl)2(CH3OH)2]Cl2·2CH3OH·4H2O (4) were synthesized through a facile solution method. Single-crystal X-ray diffraction analyses reveal that complexes 1-4 consist of a [Ln2CoII4CoIII4] core, which is constructed by bridging a quasi-double cuboidal [Ln2CoII2CoIII2] core with two [CoIICoIII] units. Electrospray ionization mass spectrometry (ESI-MS) using methanol solution reveals that complexes 1-4 are stable in the solution, and the clusters undergo three different substitution reactions (Cl- replaced by OH-, OH- replaced by CH3O- and HCOO- replaced by OH-/CH3O-) at the same time in the ionization state. Magnetic susceptibilities reveal ferromagnetic couplings within complexes 3 and 4, and the magnetocaloric effect (MCE) for 2 was also evaluated and the maximum entropy change (-ΔSm) value reaches 16.3 J kg-1 K-1 at about 3 K and 5 T.

Quantum Monte Carlo simulations of a giant {Ni21Gd20} cage with a S = 91 spin ground state

The detailed analysis of magnetic interactions in a giant molecule is difficult both because the synthesis of such compounds is challenging and the number of energy levels increases exponentially with the magnitude and number of spins. Here, we isolated a {Ni₂₁Gd₂₀} nanocage with a large number of energy levels (≈5 × 10³⁰) and used quantum Monte Carlo (QMC) simulations to perform a detailed analysis of magnetic interactions. Based on magnetization measurements above 2 K, the QMC simulations predicted very weak ferromagnetic interactions that would give a record S = 91 spin ground state. Low-temperature measurements confirm the spin ground state but suggest a more complex picture due to the single ion anisotropy; this has also been modeled using the QMC approach. The high spin and large number of low-lying states lead to a large low-field magnetic entropy (14.1 J kg^-1 K^-1 for ΔH = 1 T at 1.1 K) for this material.

Multifunctional luminescent magnetic cryocooler in a Gd5Mn2 pyramidal complex

Magnetic cooling is a highly efficient refrigeration technique with the potential of replacing expensive and rare helium-3 in the field of ultra-low temperature cooling. However, the visualization of a cryogen at an extremely low temperature and in a strong magnetic field is challenging, but it is crucial for the precise positioning and in situ thermal probe measurements in potential practical applications. Here, the activation of a red-emissive Mn(ii) ion using 3d/4f chemistry produces a luminescent molecule cooler, [Gd5Mn2(LOMe)2(OH)4(Ac)6(MeOH)10Cl2]Cl3·2MeOH (1), with the core of an Mn(ii)-anchored heptanuclear [GdIII5MnII2] pyramid. The photoluminescence (PL) of the Mn2+ emission, with a large Stokes shift (λem ∼ 690 nm) from 4T1(4G) → 6A1(6S), shows not only a sensitive temperature sensing property but also reversible mechanoluminescence (ML). More attractively, these findings reveal a considerable magnetocaloric effect (MCE) coupled with a tunable emission window, opening up new opportunities in the multifunctional applications of PL, ML, and the MCE involving red-light sources, thermometers, and stress imaging. In particular, this provides a novel resolution to design visualized PL coolers.

Site preferences in hetero-metallic [Fe9-xNix] clusters: a combined crystallographic, spectroscopic and theoretical analysis

The reaction of mixtures of Fe(O₂CMe)₂·2H₂O and Ni(O₂CMe)₂·4H₂O of various compositions with di-2-pyridyl ketone (py₂CO, dpk) in MeCN under an inert atmosphere afforded a family of hetero-metallic enneanuclear clusters with general formula [Fe_9-xNi_x(μ₄-OH)₂(O₂CMe)₈(py₂CO₂)₄] (2, x = 1.00; 3: x = 6.02; 4, x = 7.46; 5, x = 7.81). Clusters 2-5 are isomorphous to the homo-metallic [Fe₉] cluster (1) previously reported by some of us, and also isostructural to the known homo-metallic [Ni₉] cluster. All four clusters contain a central M^II ion in an unusual 8-coordinate site and eight peripheral M^II ions in distorted octahedral environments. The distribution of Fe^II and Ni^II ions over these two distinct coordination sites in 2-5 can be established through a combination of X-ray fluorescence and Mössbauer spectroscopies, which show that Fe^II preferentially occupies the unique 8-coordinate metal site while Ni^II accumulates in the octahedral holes. Density functional theory indicates that the distribution of ions across the two sites arises not from any intrinsic preference of the Fe^II ions for the 8-coordinate sites, but rather because of the large ligand field stabilization energy available to Ni^II in octahedral coordination.

A topologically unique alternating {CoIII3GdIII3} magnetocaloric ring

A building block approach to molecule-based refrigerants: using diamagnetic Co(iii) to decrease the interaction between Gd(iii) ions and hence, enhance the adiabatic temperature change.

Lantern-shaped 3d–4f high-nuclearity clusters with magnetocaloric effect

Two lantern-shaped, high-nuclearity 3d–4f clusters were synthesized by using iminodiacetic acid (IDA) and isonicotinic acid (HIN) as the co-ligand under solvothermal conditions. Magnetic studies show a large magnetocaloric effect (MCE) for the gadolinium analogue.

pH-Dependent Self-Assembly of Ladder-Like Lanthanide Chains with Copper(I) Halide Clusters

Through adjustment of the pH value of the reaction system, two series of 3 D lanthanide(III)-copper(I) coordination polymers, namely [Ln₂ (na)₇ Cu₆ Br₅ (H₂ O)₂ ] [Ln=La (1), Ce (2), Pr (3), Nd (4), Sm (5), Eu (6), Gd (7), Tb (8)] and [La₂ (na)₇ Cu₃ Br₂ (H₂ O)₂ ]⋅H₂ O (9) (na^- =nicotinate), are synthesized hydrothermally and characterized fully. It is worth nothing that these two series of heterometallic compounds are constructed from similar ladder-like Ln-organic chains, but different copper(I) halide clusters. The luminescence properties of the compounds with Nd (4), Eu (6), and Tb (8) are also investigated.

Coordination-Cluster-Based Molecular Magnetic Refrigerants

Coordination polymers serving as molecular magnetic refrigerants have been attracting great interest. In particular, coordination cluster compounds that demonstrate their apparent advantages on cryogenic magnetic refrigerants have attracted more attention in the last five years. Herein, we mainly focus on depicting aspects of syntheses, structures, and magnetothermal properties of coordination clusters that serve as magnetic refrigerants on account of the magnetocaloric effect. The documented molecular magnetic refrigerants are classified into two primary categories according to the types of metal centers, namely, homo- and heterometallic clusters. Every section is further divided into several subgroups based on the metal nuclearity and their dimensionalities, including discrete molecular clusters and those with extended structures constructed from molecular clusters. The objective is to present a rough overview of recent progress in coordination-cluster-based molecular magnetic refrigerants and provide a tutorial for researchers who are interested in the field.

Phosphonate Based High Nuclearity Magnetic Cages

Transition metal based high nuclearity molecular magnetic cages are a very important class of compounds owing to their potential applications in fabricating new generation molecular magnets such as single molecular magnets, magnetic refrigerants, etc. Most of the reported polynuclear cages contain carboxylates or alkoxides as ligands. However, the binding ability of phosphonates with transition metal ions is stronger than the carboxylates or alkoxides. The presence of three oxygen donor sites enables phosphonates to bridge up to nine metal centers simultaneously. But very few phosphonate based transition metal cages were reported in the literature until recently, mainly because of synthetic difficulties, propensity to result in layered compounds, and also their poor crystalline properties. Accordingly, various synthetic strategies have been followed by several groups in order to overcome such synthetic difficulties. These strategies mainly include use of small preformed metal precursors, proper choice of coligands along with the phosphonate ligands, and use of sterically hindered bulky phosphonate ligands. Currently, the phosphonate system offers a library of high nuclearity transition metal and mixed metal (3d-4f) cages with aesthetically pleasing structures and interesting magnetic properties. This Account is in the form of a research landscape on our efforts to synthesize and characterize new types of phosphonate based high nuclearity paramagnetic transition metal cages. We quite often experienced synthetic difficulties with such versatile systems in assembling high nuclearity metal cages. Few methods have been emphasized for the self-assembly of phosphonate systems with suitable transition metal ions in achieving high nuclearity. We highlighted our journey from 2005 until today for phosphonate based high nuclearity transition metal cages with V(IV/V), Mn(II/III), Fe(III), Co(II), Ni(II), and Cu(II) metal ions and their magnetic properties. We observed that slight changes in stoichiometry, reaction conditions, and presence or absence of coligand played crucial roles in determining the final structure of these complexes. Most of the complexes included are regular in geometry with a dense arrangement of the above-mentioned metal centers in a confined space, and a few of them also resemble regular polygonal solids (Archimedean and Platonic). Since there needs to be a historical approach for a comparative study, significant research output reported by other groups is also compared in brief to ensure the potential of phosphonate ligands in synthesizing high nuclearity magnetic cages.

Understanding the magnetism of {Fe2Ln} dimers, step-by-step

A hierarchical, comparative approach to the complex magnetochemistry of {Fe₄M₂}-type coordination clusters (M = Y, Eu, Gd, Dy) allows determination of intramolecular exchange energies.