A keplerate magnetic cluster featuring an icosidodecahedron of Ni(II) ions encapsulating a dodecahedron of La(III) ions

Assembly of Homochiral Magneto-Optical Dy6 Triangular Clusters by Fixing Carbon Dioxide in the Air

A new hydrazone Schiff base bridging ligand (H2LSchiff (E)-N'-((1-hydroxynaphthalen-2-yl)methylene)pyrazine-2-carbohydrazide) and L/D-proline were used to construct a pair of homochiral Dy6 cluster complexes, [Dy6(CO3)(L-Pro)6(LSchiff)4(HLSchiff)2]·5DMA·2H2O (L-1, L-HPro = L-proline; DMA = N,N-dimethylacetamide) and [Dy6(CO3)(D-Pro)6(LSchiff)4(HLSchiff)2]·5DMA·2H2O (D-1, D-HPro = D-proline), which show a novel triangular Dy6 topology. Notably, the fixation of CO2 in the air formed a carbonato central bridge, playing a key role in assembling L-1/D-1. Magnetic measurements revealed that L-1/D-1 displays intramolecular ferromagnetic coupling and magnetic relaxation behaviours. Furthermore, L-1/D-1 shows a distinct magneto-optical Faraday effect and has a second harmonic generation (SHG) response (1.0 × KDP) at room temperature. The results show that the immobilization of CO2 provides a novel pathway for homochiral multifunctional 4f cluster complexes.

Icosidodecahedral Coordination-Saturated Cuprofullerene

The first coordination-saturated buckyball with a C60 molecule totally encased in an icosidodecahedral Cu30 in a (μ30 -(η2 )30 )-fashion, namely C60 @Cu30 @Cl36 N12 , has been successfully realized by a C60 -templated assembly. The 48 outmost coordinating atoms (36Cl+12N) comprise a new simple polyhedron that is described by a ccf topology. Charge transfer from (CuI , Cl) to C60 explains the expansion of the light absorption up to 700 nm, and accounts for an ultrafast photophysical process that underpins its high photothermal conversion efficiency. This work makes a giant step forward in exohedral metallofullerene (ExMF) chemistry.

Platonic and Archimedean solids in discrete metal-containing clusters

Metal-containing clusters have attracted increasing attention over the past 2-3 decades. This intense interest can be attributed to the fact that these discrete metal aggregates, whose atomically precise structures are resolved by single-crystal X-ray diffraction (SCXRD), often possess intriguing geometrical features (high symmetry, aesthetically pleasing shapes and architectures) and fascinating physical properties, providing invaluable opportunities for the intersection of different disciplines including chemistry, physics, mathematical geometry and materials science. In this review, we attempt to reinterpret and connect these fascinating clusters from the perspective of Platonic and Archimedean solid characteristics, focusing on highly symmetrical and complex metal-containing (metal = Al, Ti, V, Mo, W, U, Mn, Fe, Co, Ni, Pd, Pt, Cu, Ag, Au, lanthanoids (Ln), and actinoids) high-nuclearity clusters, including metal-oxo/hydroxide/chalcogenide clusters and metal clusters (with metal-metal binding) protected by surface organic ligands, such as thiolate, phosphine, alkynyl, carbonyl and nitrogen/oxygen donor ligands. Furthermore, we present the symmetrical beauty of metal cluster structures and the geometrical similarity of different types of clusters and provide a large number of examples to show how to accurately describe the metal clusters from the perspective of highly symmetrical polyhedra. Finally, knowledge and further insights into the design and synthesis of unknown metal clusters are put forward by summarizing these "star" molecules.

Hierarchical Assembly of Coordination Macromolecules with Atypical Geometries: Gd44 Co28 Crown and Gd95 Co60 Cage

The discovered giant clusters are always highly symmetric owing to the spontaneous assembly of one or two basic units. Herein we report the Gd₄₄ Co₂₈ crown and Gd₉₅ Co₆₀ cage, formulated as [Gd₄₄ Co₂₈ (IDA)₂₀ (OH)₇₂ (CO₃ )₁₂ (OAc)₂₈ (H₂ O)₆₄ ]⋅(ClO₄ )₂₄ and [Na₄ Gd₉₅ Co₆₀ (IDA)₄₀ (OH)₁₅₀ (CO₃ )₄₀ (OAc)₅₈ (H₂ O)₁₆₄ ] ⋅ (ClO₄ )₄₁ (H₂ IDA=iminodiacetic acid), respectively, by providing a library containing multiple low-nuclearity units. The heart-like units and crown-like tetramer found in both compounds indicate unprecedented assembly levels, leading to an atypical geometry characteristic compared to the giant clusters directly assembled by regular units. These two clusters not only significantly increase the size of Ln-Co clusters but also exhibit the enhanced magnetic entropy change at ultra-low temperatures. This work provided an effective way to fabricate cluster compounds with giant size and geometry complexity simultaneously.

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...

A High-Symmetry Double-Shell Gd30Co12 Cluster Exhibiting a Large Magnetocaloric Effect

A high-nuclearity 3d-4f cluster of [Gd₃₀Co^II₆Co^III₆(OH)₅₆(NO₃)₁₂(CH₃COO)₃₀(H₂O)₃₀]·(NO₃)₂₂·(en)₃·(H₂O)₃ (1) was synthesized through the reaction of Gd(NO₃)₃·6H₂O, Co(NO₃)₂·6H₂O, and sodium acetate in a mixture of ethanediamine (en), ethanol, and deionized water. The cluster core in 1 features a double-shell structure with a Co₁₂ icosahedron encapsulating a Gd₃₀ icosidodecahedron. A magnetic study reveals that separating Co²⁺ ions with Gd³⁺ ions can effectively reduce the magnetic interaction of 3d-4f clusters. Significantly, the magnetocaloric effect (MCE) of 1 at 2 K and 7 T is up to 44.7 J kg^-1 K^-1, the largest MCE reported to date in the 3d-4f metal clusters.

Snapshots of Ce70 Toroid Assembly from Solids and Solution

Crystallization at the solid-liquid interface is difficult to spectroscopically observe and therefore challenging to understand and ultimately control at the molecular level. The Ce₇₀-torroid formulated [Ce^IV₇₀(OH)₃₆(O)₆₄(SO₄)₆₀(H₂O)₁₀]^4-, part of a larger emerging family of M^IV₇₀-materials (M = Zr, U, Ce), presents such an opportunity. We elucidated assembly mechanisms by the X-ray scattering (small-angle scattering and total scattering) of solutions and solids as well as crystallizing and identifying fragments of Ce₇₀ by single-crystal X-ray diffraction. Fragments show evidence for templated growth (Ce₅, [Ce₅(O)₃(SO₄)₁₂]^10-) and modular assembly from hexamer (Ce₆) building units (Ce₁₃, [Ce₁₃(OH)₆(O)₁₂(SO₄)₁₄(H₂O)₁₄]^6- and Ce₆₂, [Ce₆₂(OH)₃₀(O)₅₈(SO₄)₅₈]^14-). Ce₆₂, an almost complete ring, precipitates instantaneously in the presence of ammonium cations as two torqued arcs that interlock by hydrogen boding through NH₄⁺, a structural motif not observed before in inorganic systems. The room temperature rapid assemblies of both Ce₇₀ and Ce₆₂, respectively, by the addition of Li⁺ and NH₄⁺, along with ion-exchange and redox behavior, invite exploitation of this emerging material family in environmental and energy applications.

A new family of decanuclear Ln7Cr3 clusters exhibiting a magnetocaloric effect

Two dimeric Ln–Cr clusters with formula {Ln(H₂O)₈[Ln₆Cr₃(L)₆(CH₃COO)₆(μ₃-OH)₁₂(H₂O)₁₂]}·(ClO₄)₆·xH₂O (Ln = Gd, x = 35 for 1 and Ln = Dy, x = 45 for 2, HL = 2-pyrazinecarboxylic acid) were obtained by a ligand-controlled hydrolytic method with a mixed ligand system (2-pyrazinecarboxylic acid and acetate). Single crystal structure analysis showed that two trigonal bipyramids of [Gd₃Cr₂(μ₃-OH)₆]⁹⁺ worked as building blocks in constructing the metal-oxo cluster core of [Gd₆Cr₃(μ₃-OH)₁₂]¹⁵⁺ by sharing a common top – a Cr³⁺ ion. Additionally, compound 1 forms a three-dimensional framework with a one-dimensional nanopore channel along the a-axis through a hydrogen-bond interaction between the cationic cluster core and the free mononuclear cation [Gd(H₂O)₈]³⁺ and the π-bond interactions of the pyrazine groups on the two cationic cluster cores. Magnetic calculations indicated a weak ferromagnetic coupling interaction for Gd⋯Gd and Gd⋯Cr in compound 1, with its magnetic entropy change (−ΔS_m) reaching 21.1 J kg⁻¹ K⁻¹ at 5 K, 7 T, while compound 2 displayed an obvious frequency-dependency at H_dc = 2000 Oe.

Two decanuclear Ln–Cr clusters Ln₇Cr₃ were obtained, which formed a three-dimensional framework with one-dimensional nanopore channel through hydrogen-bond and π-bond interactions. Gd₇Cr₃ had a magnetic entropy change of 21.1 J kg⁻¹ K⁻¹ at 5 K, 7 T.

A rod-like hexanuclear nickel cluster based on a bi(pyrazole-alcohol) ligand: structure, electrospray ionization mass spectrometry, magnetism and photocurrent response

An unusual one-dimensional zig-zag hexanuclear Ni(ii) cluster has been easily and successfully constructed using a designed multidentate pyrazole-alcohol ligand.

A Novel Family of Triangular CoII2LnIII and CoII2YIII Clusters by the Employment of Di-2-Pyridyl Ketone

The synthesis, structural characterization and magnetic study of novel CoII/4f and CoII/YIII clusters are described. In particular, the initial employment of di-2-pyridyl ketone, (py)2CO, in mixed metal Co/4f chemistry, provided access to four triangular clusters, [CoII2MIII{(py)2C(OEt)(O)}4(NO3)(H2O)]2[M(NO3)5](ClO4)2 (M = Gd, 1; Dy, 2; Tb, 3; Y, 4), where (py)2C(OEt)(O)− is the monoanion of the hemiketal form of (py)2CO. Clusters 1–4 are the first reported Co/4f (1–3) and Co/Y (4) species bearing (py)2CO or its derivatives, despite the fact that over 200 metal clusters bearing this ligand have been reported so far. Variable-temperature, solid-state dc and ac magnetic susceptibility studies were carried out on 1–4 and revealed the presence of weak ferromagnetic exchange interactions between the metal ions (JCo-Co = +1.3 and +0.40 cm−1 in 1 and 4, respectively; JCo-Gd = +0.09 cm−1 in 1). The ac susceptibility studies on 2 revealed nonzero, weak out-of-phase (χ’’M) signals below ~5 K.

Cation sensing by luminescent high-nuclearity Zn–Eu Schiff base nanoscale complexes: high sensitivity to Ag+ and Cd2+ ions at the ppm level

Two types of Zn–Ln nanoscale complexes were constructed using Schiff base ligands, and the 12-metal Zn–Eu complex shows interesting luminescent sensing of metal cations.

Theoretical investigation of M@Pb122- and M@Sn122- Zintl clusters (M = Lrn+, Lun+, La3+, Ac3+ and n = 0, 1, 2, 3)

The positions of lawrencium (Lr), lutetium (Lu), actinium (Ac) and lanthanum (La) in the periodic table have been a controversial topic for quite some time. According to studies carried out by different groups with their justifications, these elements may potentially be placed in the d-block, p-block or all four in a 15 element f-block. The present work looks into this issue from a new perspective, which involves encapsulation of these four elements into Zintl ion clusters, Pb122- and Sn122-, followed by the determination of the structural, thermodynamic and electronic properties of these endohedral M@Pb122- and M@Sn122- clusters (M = Lrn+, Lun+ with n = 0, 1, 2, 3) using first principles based density functional theory (DFT). These parameters are compared with similar clusters encapsulated La3+ and Ac3+ ions in order to seek out similarities and differences to draw conclusions about their placement in the periodic table. For the first time the structural, energetic, and electronic properties of these metal atom/ion encapsulated Pb122- and Sn122- clusters have been investigated thoroughly. Structural parameters such as bond distances, geometry and symmetry, electronic properties viz. the density of states, the molecular orbital ordering, the electron localization function, bond critical point properties and charge distributions have been analyzed. Additionally, the thermodynamic property of the binding energy during the encapsulation process has also been calculated. All M@Pb12+ and M@Sn12+ (M = Lr and Lu) clusters form stable 18 bonding electron magic number systems with shell closing. They show negative values of binding energy and relatively large HOMO-LUMO energy gaps indicating the stability of such clusters. All the calculated parameters for Lr encapsulated clusters closely match with the corresponding calculated parameters of Lu encapsulated clusters, confirming the similarity between Lr and Lu metal atoms in various oxidation states, though their atomic ground state valence electronic configurations are different. The effect of spin orbit coupling has also been investigated using the ZORA approach. It is interesting to discover that La and Ac showed striking similarities to Lr and Lu with respect to all the properties investigated and have formed a stable 18-electron system.

A self-assembling luminescent lanthanide molecular nanoparticle with potential for live cell imaging

Four luminescent 32-metal Cd-Tb nanoclusters, [Tb₈Cd₂₄(L¹)₁₂(OAc)₄₈] (1), [Tb₈Cd₂₄(L²)₁₂(OAc)₄₈] (2), [Tb₈Cd₂₄(L³)₁₂(OAc)₄₈] (3) and [Tb₈Cd₂₄(L²)₁₂(1,4-BDC)₄(OAc)₃₈(OH)₂] (4), were constructed from three specially designed chain-like Schiff base ligands H₂L^1-3 with flexible carbon-carbon backbones containing 5, 6 and 10 methylene units, respectively. The clusters exhibit drum-like structures and can be imaged using transmission electron microscopy (TEM). In addition to the Schiff base ligands (the primary energy transfer donors), four 1,4-BDC bridging units were successfully introduced into the structure of 4. In addition to providing increased structural stability, the 1,4-BDC units act as secondary energy transfer donors providing extra energy for lanthanide luminescence, which results in improved luminescence properties when compared to those of the related Cd-Ln nanoclusters without 1,4-BDC units. In vitro investigations on 4 with SGC and PANC cancer cells revealed an accumulation of the molecular nanoparticles in the cells, as confirmed by confocal microscopy. The cytotoxicity of 4 toward the SGC and PANC cells is moderate (IC₅₀ values of 4 lie in the range of 15-60 μM). ICP-MS analysis reveals that cellular uptakes of 4 in 1000 SGC and PANC cells after treatment for 3 hours are 0.0094 pmol and 0.015 pmol, respectively.

High-Nuclearity Lanthanide-Containing Clusters as Potential Molecular Magnetic Coolers

High-nuclearity cluster-type metal complexes are a unique class of compounds, many of which have aesthetically pleasing molecular structures. Their interesting physical and chemical properties arise primarily from the electronic and/or magnetic interplay between the component metal ions. Among the extensive studies in the past two decades, those on lanthanide-containing clusters, lanthanide-exclusive or heterometallic with transition metal elements, are most notable. The research was driven by both the synthetic challenges for these generally elusive species and their intriguing magnetic properties, which are useful for the development of energy-efficient and environmentally friendly magnetic cooling technologies. Our efforts in this vein have been concentrated on developing rational synthetic methods for high-nuclearity lanthanide-containing clusters. By means of the now widely adopted approach of "ligand-controlled hydrolysis" of lanthanide ions, a great variety of cluster-type lanthanide hydroxide complexes had been prepared in the first half of this developing period (1999-2006). In this Account, our efforts since 2007 are summarized. These include (1) further development of synthetic strategies in order to expand the ligand scope and/or to increase the nuclearity (>25) of the cluster species and (2) magnetic studies pertinent to the pursuit of materials with a large magnetocaloric effect (MCE). Specifically, with the hope of expanding the family of ligands and producing clusters of previously unknown structures, we tested under hydrothermal or solvothermal conditions the use of readily available yet not commonly used ligands for controlling lanthanide hydrolysis; such ligands, carboxylates as mundane examples, tend to form insoluble complexes prior to any possible hydrolysis. We have also validated the use of preformed transition metal complexes as metalloligands for subsequent control of lanthanide hydrolysis toward heterometallic 3d-4f clusters. Furthermore, we demonstrated using ample examples that the presence of small anions as templates is essential to the assembly of high-nuclearity lanthanide-containing clusters and that maintaining a low concentration of the anion template(s) is a key to such success. It has been found that slow production/release of such anion templates by in situ ligand decomposition or absorption of atmospheric CO₂ is effective in preventing precipitation of their lanthanide salts, allowing not only controllable lanthanide hydrolysis but also gradual and modular assembly of the giant cluster species. Magnetic studies targeting potential applications of such clusters as molecular magnetic coolers have also been conducted. The results are summarized in the second portion of this Account in an effort to establish a certain magneto-structure relationship. Of particular relevance is the possible correlation between MCE (evaluated using the isothermal magnetic entropy change, -ΔS_M) and magnetic density, and the intracluster antiferromagnetic exchange coupling. We have also made some preliminary attempts at preparing processable and practically useful materials in the form of a monodisperse core-shell nanostructure. We succeeded in encapsulating a single nanosized heterometallic molecular cluster in a nanoshell of silica. It was found that such passivation not only helped stabilize the cluster but also reduced the magnetic interactions between individual clusters. These effects are reflected in the slightly enhanced value of -ΔS_M for the core-shell composite over the parent unprotected cluster.

A homochiral Zn–Dy heterometallic left-handed helical chain complex without chiral ligands: anion-induced assembly and multifunctional integration

The Zn₃Dy₂ pentanuclear complex evolved into a heterometallic left-handed helical chain multifunctional complex by the template action of perchlorate anion.

Four 3d–4f heterometallic Ln45M7 clusters protected by mixed ligands

A series of high-nuclearity 3d–4f clusters Ln₄₅M₇ were obtained based on acetate and propionate as mixed protecting ligands and ClO₄⁻ and CO₃²⁻ as mixed anion templates.

A [Ce21] keplerate

The solvothermal reaction between Ce(NO₃)₃·6H₂O, 2-amino-isobutyric acid, 2-hydroxy-1-naphthaldehyde and 2-amino-2-methyl-1,3-propanediol in MeOH, in the presence of base, leads to the formation of a unique [CeCe ] keplerate cage.

Isolation, structure and magnetic properties of two novel core-shell 3d-4f heterometallic nanoscale clusters

Two novel core-shell Ni-Ln nanosized clusters, Na₄(H₃O)₄[Nd₃₈Ni_42.5(IDA)₄₂(OAc)₄(CH₃CH₂OH)₂(CO₃)₁₈(μ₃-OH)₆₂(μ₃-O)₆(H₂O)₁₂]Cl₆·26H₂O (1) and Na[Pr₄₂Ni₃₈(μ₃-OH)₇₁(μ₃-O)₄(IDA)₃₈(NH₂CH₂COO)₂(OAc)₂(CH₃CH₂OH)₂(CO₃)₁₆(H₂O)₆Cl₇]Cl₃·37H₂O (2) (IDA = iminodiacetate), were successfully prepared using the Cl^- anion and the flexible ligand iminodiacetic acid. Structural analysis indicates that the discrete dumbbell-shaped 3d-4f heterometallic cluster in 1 is constructed from two {Nd₁₉Ni₂₁} clusters connected by one {NiO₆} unit, whereas the bowknot-shaped nanosized cluster is composed of two {Pr₁₉Ni₁₉} clusters ligated by two {Pr₂} units and CO₃^2- anions. The formation of both compounds indicates that Cl^- ions play important roles and act not only as balance anions but also as template and bridging ligands. The magnetic properties of compounds 1 and 2 were investigated, and it was revealed that they display dominant antiferromagnetic exchange.

Enhancement of the luminescence properties of high-nuclearity Cd-Ln (Ln = Eu and Nd) nanoclusters by the introduction of more energy transfer donors

Two Cd-Ln clusters [Ln₈Cd₂₄L₁₂(1,4-BDC)₄(OAc)₃₈(OH)₂] (Ln = Eu (1) and Nd (2)) were constructed using a flexible Schiff base and rigid 1,4-BDC ligands. The Cd-Ln clusters exhibit interesting nano-drum-like structures which allow direct visualization by TEM. The introduced 1,4-BDC units act as efficient energy transfer donors for lanthanide luminescence, resulting in superior luminescence properties of 1 and 2.

[Cd(H2O)6]@{Cd6Cl4(nico)12[Hg(Tab)2(μ-Cl)]2}: a heterometallic host–guest icosidodecahedron cage via hierarchical assembly

A reaction of [Hg(Tab)₂(nico)](PF₆) (Tab = 4-(trimethylammonio)benzenethiolate, nico = nicotinate) with equimolar CdCl₂·2.5H₂O afforded a unique heterometallic cage complex [Cd(H₂O)₆]@{Cd₆Cl₄(nico)₁₂[Hg(Tab)₂(μ-Cl)]₂}.

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.

Anisotropic lanthanide-based nano-clusters for imaging applications

We have developed a new class of lanthanide nano-clusters that self-assemble using flexible Schiff base ligands. Cd-Ln and Ni-Ln clusters, [Ln8Cd24(L1)12(OAc)39Cl7(OH)2] (Ln = Nd, Eu), [Eu8Cd24(L1)12(OAc)44], [Ln8Cd24(L2)12(OAc)44] (Ln = Nd, Yb, Sm) and [Nd2Ni4(L3)2(acac)6(NO3)2(OH)2], were constructed using different types of flexible Schiff base ligands. These molecular nano-clusters exhibit anisotropic architectures that differ considerably depending upon the presence of Cd (nano-drum) or Ni (square-like nano-cluster). Structural characterization of the self-assembled particles has been undertaken using crystallography, transmission electron microscopy and small-angle X-ray scattering. Comparison of the metric dimensions of the nano-drums shows a consistency of size using these techniques, suggesting that these molecules may share similar structural features in both solid and solution states. Photophysical properties were studied by excitation of the ligand-centered absorption bands in the solid state and in solution, and using confocal microscopy of microspheres loaded with the compounds. The emissive properties of these compounds vary depending upon the combination of lanthanide and Cd or Ni present in these clusters. The results provide new insights into the construction of novel high-nuclearity nano-clusters and offer a promising foundation for the development of new functional nanomaterials.

Filling the gap between the quantum and classical worlds of nanoscale magnetism: giant molecular aggregates based on paramagnetic 3d metal ions

In this review, aspects of the syntheses, structures and magnetic properties of giant 3d and 3d/4f paramagnetic metal clusters in moderate oxidation states are discussed. The term "giant clusters" is used herein to denote metal clusters with nuclearity of 30 or greater. Many synthetic strategies towards such species have been developed and are discussed in this paper. Attempts are made to categorize some of the most successful methods to giant clusters, but it will be pointed out that the characteristics of the crystal structures of such compounds including nuclearity, shape, architecture, etc. are unpredictable depending on the specific structural features of the included organic ligands, reaction conditions and other factors. The majority of the described compounds in this review are of special interest not only for their fascinating nanosized structures but also because they sometimes display interesting magnetic phenomena, such as ferromagnetic exchange interactions, large ground state spin values, single-molecule magnetism behaviour or impressively large magnetocaloric effects. In addition, they often possess the properties of both the quantum and the classical world, and thus their systematic study offers the potential for the discovery of new physical phenomena, as well as a better understanding of the existing ones. The research field of giant clusters is under continuous evolution and their intriguing structural characteristics and magnetism properties that attract the interest of synthetic Inorganic Chemists promise a brilliant future for this class of compounds.

Assembly of polyoxometalates and Ni-bpy cationic units into the molecular core–shell structures as bifunctional electrocatalysts

Four core–shell organic–inorganic hybrid materials composed of polyoxometalates and Ni-bpy units were designed and synthesized, which exhibited bifunctional electrocatalytic activity for the reduction of NO₂⁻ and water oxidation.

{NiII8LnIII6} (Ln = Gd, Dy) rod-like nano-sized heteronuclear coordination clusters with a double carbonate bridge skeleton and remarkable MCE behaviour

We prepared through CO₂ air fixation novel Ni₈Ln₆ complexes showing a remarkable μ₅-carbonate bridged octanuclear planar {Ni₄Ln₄} core and unusual MCE behaviour.

Nitronyl nitroxide based 2p-3d-4f chains with the magnetocaloric effect and slow magnetic relaxation

Four new nitronyl nitroxide radical based hetero-tri-spin one-dimensional compounds, namely [{Ln(hfac)3}3{Cu(hfac)2}{NIT-Ph(OMe)2}4]n (Ln = Gd (1), Tb (2), Dy (3), Er (4); hfac = hexafluoroacetylacetonate; NIT-Ph(OMe)2 = 2-(2',4'-dimethoxyphenyl)-4,4,5,5-tetramethyl-imidazolyl-1-oxyl-3-oxide) have been successfully prepared. Single crystal X-ray crystallographic analysis reveals that complexes 1-4 possess a 1D chain structure with a repeating [Cu-Rad-Ln-Rad-Ln-Rad-Ln-Rad] moiety in which Ln(hfac)3 and Cu(hfac)2 units are bridged by nitronyl nitroxide radicals through the NO groups. DC magnetic studies found that ferromagnetic interactions between metals and the coordinated NO groups are active in all four compounds. The Tb derivative displays frequency dependent ac magnetic susceptibilities, indicating slow magnetic relaxation behavior. The Gd complex shows an important cryogenic magnetocaloric effect with the entropy change (-ΔSm) of 13.5 J kg(-1) K(-1) at 2 K and a magnetic field of 7 T, representing the first example of Gd-radical molecular species exhibiting the magnetocaloric effect.