A Gigantic Molecular Wheel of {Gd140}: A New Member of the Molecular Wheel Family

Modulated assembly and structural diversity of heterometallic Sn-Ti oxo clusters from inorganic tin precursors

Through modulating the multidentate ligands, solvent environments, and inorganic tin precursors during the synthesis processes, we have successfully prepared a series of unprecedented heterometallic Sn-Ti oxo clusters with structural diversity and different physiochemical attributes. Initially, two Sn6Ti10 clusters were synthesized using trimethylolpropane as a structure-oriented ligand and SnCl4·5H2O as a tin source. Then, when a larger pentadentate ligand di(trimethylolpropane) was used instead of trimethylolpropane and aprotic acetonitrile solvent was introduced into the reaction system, four low-nuclearity Sn-Ti oxo clusters were discovered, including two Sn1Ti1, one Sn2Ti2 and one Sn2Ti6. Finally, two mixed-valence state clusters, SnII4SnIV2TiIV14 and SnII4SnIV4TiIV20, were obtained by transforming the tin precursor from SnCl4·5H2O to SnCl2·2H2O and adjusting the acetonitrile solution with trace acetic acid/formic acid. Sn8Ti20 is the highest-nuclearity heterometallic Sn-Ti oxo cluster to date. Moreover, comparative electrocatalytic CO2 reduction experiments were carried out, and it was concluded that the Sn8Ti20-decorated electrode showed the most satisfactory performance due to the influence of mixed-valence states of the Sn atoms and the charging effects provided by 20 Ti4+ ions. This study presents important guiding significance for the design, synthesis and application optimization of functional heterometallic nanoclusters.

Magnetocaloric effect in 1D-polymers bearing 15-metallacrown-5 {GdCu5}3+ units and anionic oxalate complexes

Two complexes {[GdCu5(GlyHA)5(H2O)7Cr(C2O4)3]·11.02H2O}n (1) and {{[GdCu5(GlyHA)5(H2O)6]μ2-[Cu(C2O4)2(H2O)]}2μ4-[Cu(C2O4)2]·15.8H2O}n (2), were obtained as outcomes of the reactions between the cationic hexanuclear {GdCu5(GlyHA)5}3+ 15-metallacrown-5 complex (where GlyHA2- = glycinehydroxamate) and the anionic oxalate complexes K3[Cr(C2O4)3] or K2[Cu(C2O4)2]. Both 1 and 2 possess polymeric 1D-chain structures according to X-ray structural analysis. As a consequence of the geometric orientations of the donor atoms in the oxalates from [Cr(C2O4)3]3-, the Cu5 mean planes of neighboring 15-metallacrown-5 units {GdCu5(GlyHA)5}3+ are angled at 75.5° to each other, which leads to formation of a zig-zag motif in the 1D-chains of complex 1. The centrosymmetric complex 2 contains two structurally different bis(oxalato)cuprate anions μ2-[Cu(C2O4)2(H2O)]2-, for one of which, coordination to two adjacent {GdCu5(GlyHA)5}3+ units leads to formation of linear 1D-chains in 2, while the second type, μ4-[Cu(C2O4)2]2-, is coordinated to four {GdCu5(GlyHA)5}3+ units, causing the cross-linking of single 1D-chains into a double-chain 1D coordination polymer. Studies of χMT vs. T data for 1 and 2 in a 2-300 K temperature range revealed the presence of both ferromagnetic and antiferromagnetic interactions amongst paramagnetic centres. The experimental χMT vs. T data for 1 were fitted using a model which takes into account exchange interactions between adjacent copper(II) ions, the Gd-Cu exchange interactions within {GdCu5(GlyHA)5}3+ units and additionally Gd-Cr exchange interactions. Fitting of the χMT vs. T data for 2 was not possible, since coordination of μ4-[Cu(C2O4)2]2- to {GdCu5(GlyHA)5}3+ led to the non-equivalence of several Cu-Cu exchange interactions within the metallacrown units and hence a superfluity of fittable parameters. Complexes 1 and 2 are the first examples of 15-metallacrown-5 complexes demonstrating a magnetocaloric effect (-ΔSM at 13 T reaches 24.26 J K-1 kg-1 at 5 K and 19.14 J K-1 kg-1 at 4 K for 1 and 2, respectively).

One-Pot In Situ Construction of a Highly Stable Acylhydrazone-Derived Dy9 Cluster with Photodynamic Sterilization Property

The extremely low stability of lanthanide clusters with precise structures and nanometer dimensions in aqueous solutions limits their application in the field of photodynamic sterilization. In this study, an hourglass-shaped nine-nucleated Dy9 cluster (1) with excellent light-driven reactive oxygen species (ROS) generation ability and photodynamic sterilization property was constructed using acylhydrazone multidentate chelating ligands obtained via an in situ reaction. The eight chelating ligands were distributed outside cluster 1, tightly wrapping the cluster core, thus preventing solvent molecules from attacking the cluster nucleus and ensuring the stability of cluster 1 in solution, which was demonstrated via X-ray diffraction and high-resolution electrospray ionization mass spectrometry (HRESI-MS). Time-dependent HRESI-MS monitoring of the self-assembly process of cluster 1 allowed two possible self-assembly mechanisms. The heavy atom effect of multiple Dy(III) ions in the Dy9 cluster enhanced the ISC pathway through spin-orbit coupling, promoting energy transfer from the excited singlet state (S1) to the triplet state (T1), which was stabilized, inducing the generation of more ROS. Cluster 1 showed a remarkable sterilization effect due to the generation of abundant ROS under light irradiation conditions. To our knowledge, this is a rare instance of lanthanide clusters with photodynamic sterilization, providing new horizons for the construction of fast and efficient sterilizers.

High-Nuclearity Ln210Al140 Clusters: Neonates of Open Hollow Dodecahedral Cage Families

Open hollow dodecahedral cage clusters have long been a coveted target in synthetic chemistry, yet their creation poses immense challenges. Here we report two open hollow dodecahedral lanthanide-aluminum (Ln-Al) heterometallic cage clusters, namely, [Ln210Al140(μ2-OH)210(μ3-OH)540(OAc)180(H2O)156](ClO4)120·(MeCN)x·(H2O)y, (Ln = Dy and x = 27, y = 300 for 1; Ln = Y and x = 28, y = 420 for 2). Remarkably, the 350 metal atoms in 1 and 2 display a Keplerate-type four-shell structure of truncated icosidodecahedron@dodecahedron@dodecahedron@icosidodecahedron. The diameter of the cationic cluster in 1 is approximately 5.0 nm, with an inner cavity diameter of about 2.8 nm and a window diameter of roughly 0.66 nm. The cluster in 1 boasts an accessible inner void volume of up to 15,000 Å3. Notably, these cage clusters maintain stability in water, and the truncated icosidodecahedrons in 1 and 2 are the first of their kind synthesized to date. Given that the open hollow dodecahedral Ln-Al cage cluster has never been reported before, this work represents a member in the family of hollow open dodecahedral cages.

Rapid and reliable ratiometric fluorescence detection of isoquercitrin based on a high-nuclearity Zn(II)-Nd(III) nanomolecular sensor

Rapid and quantitative detection of isoquercitrin (Isq) has been attracting much attention due to its outstanding pharmacological and physiological activities. Herein, an interesting 48-metal Zn(II)-Nd(III) nanocluster (1, molecular sizes 1.3 × 2.8 × 3.1 nm) with salen-type Schiff base ligand was constructed as molecular sensor for the luminescence detection of Isq. 1 exhibits visible ligand-centered emission and NIR luminescence of Nd(III), and shows ratiometric fluorescence response to Isq with high sensitivity even in the presence of other interferences. The fluorescence sensing behavior can be expressed by a second-order equation I1060nm/I480nm = A*[Isq]2 + B*[Isq] + C, which is used to quantitatively analyze the Isq concentrations in DMF and FCS. The LODs to Isq for the ligand-centered and lanthanide emissions of 1 in DMF are 0.21 μM and 0.11 nM, respectively. The quenching of the ligand-centered emission of 1 caused by Isq is attributed to the competitive absorption of light energy and "inner effect", while, the luminescence enhancement is due to the "antenna effect".

Aluminum Molecular Ring Meets Deep Eutectic Solvents: Adaptive Assembly and Optical Behavior

Different from the previous neutral reaction solvent system, this work explores the synthesis of Al-oxo rings in ionic environments. Deep eutectic solvents (DESs) formed by quaternary ammonium salts hydrogen bond acceptor (HBA) and phenols hydrogen bond donor (HBD) further reduce the melting point of the reaction system and provide an ionic environment. Further, the quaternary ammonium salt was chosen as the HBA because it contains a halogen anion that matches the size of the central cavity of the molecular ring. Based on this thought, five Al8 ion pair cocrystals were synthesized via "DES thermal". The general formula is Q+ ⊂ {Cl@[Al8(BD)8(μ2-OH)4L12]} (AlOC-180-AlOC-185, Q+ = tetrabutylammonium, tetrapropylammonium, 1-butyl-3-methylimidazole; HBD = phenol, p-chlorophenol, p-fluorophenol; HL = benzoic acid, 1-naphthoic acid, 1-pyrenecarboxylic acid, anthracene-9-carboxylic acid). Structural studies reveal that the phenol-coordinated Al molecular ring and the quaternary ammonium ion pair form the cocrystal compounds. The halogen anions in the DES component are confined in the center of the molecular ring, and the quaternary ammonium cations are located in the organic shell. Such an adaptive cocrystal binding pattern is particularly evident in the structures coordinated with low-symmetry ligands such as naphthoic acid and pyrene acid. Finally, the optical behavior of these cocrystal compounds is understood from the analysis of crystal structure and theoretical calculation.

Self-Assembly of four Ni16 Molecular Wheels with Capsule and Tubular Supramolecular Architectures

Four new Ni16 molecular wheels with the general formula [L4Ni16(RCOO)16(H2O)x(MeOH)12-x] (where H4L=1,4-bis((E)-((2'-hydroxybenzyl)imino)methyl)-2,3-naphthalenediol, and R=H or Me) have been isolated and structurally characterised. Complexes C1-C3 (R=Me) were formed using nickel (II) acetate and presented as polymorphs with the same formulation of charged components. The same wheel-like architecture was observed in C4 (R=H), which was prepared using nickel (II) formate, demonstrating the potential for further versatility of the system. In contrast to similar four-fold symmetric Ni(II) wheel clusters, measurements of the static magnetic properties of C1 indicated the presence of dominant antiferromagnetic interactions and an S=0 ground state.

A Hexanuclear Gadolinium(III)-Based Nanoprobe for Magnetic Resonance Imaging of Tumor Apoptosis

Magnetic resonance imaging (MRI) is instrumental in the noninvasive evaluation of tumor tissues in patients subjected to chemotherapy, thereby yielding essential diagnostic data crucial for the prognosis of tumors and the formulation of therapeutic strategies. Currently, commercially available MRI contrast agents (CAs) predominantly consist of mononuclear gadolinium(III) complexes. Because there is only one Gd(III) atom per molecule, these CAs often require administration in high doses to achieve the desired contrast quality, which inevitably leads to some adverse events. Herein, we develop a six-nuclei, apoptosis-targeting T1 CA, Gd6-ZnDPA nanoprobe, which consists of a hexanuclear gadolinium nanocluster (Gd6) with an apoptosis-targeting group (ZnDPA). The amplification of Gd(III) by the hexanuclear structure generates its high longitudinal relaxivity (44.67 mM-1 s-1, 1T) and low r1/r2 ratio (0.68, 1T). Based on the Solomon-Bloembergen-Morgan (SBM) theory, this notable improvement is primarily ascribed to a long correlation tumbling time (τR). More importantly, the Gd6-ZnDPA nanoprobe shows excellent tumor apoptosis properties with an enhanced MR signal ratio (∼74%) and a long MRI imaging acquisition time window (∼48 h) in 4T1 tumor-bearing mice. This study introduces an experimental gadolinium-based CA for the potential imaging of tumor apoptosis in the context of MRI.

Polyoxometalate-Structured Materials: Molecular Fundamentals and Electrocatalytic Roles in Energy Conversion

Polyoxometalates (POMs), a kind of molecular metal oxide cluster with unique physical-chemical properties, have made essential contributions to creating efficient and robust electrocatalysts in renewable energy systems. Due to the fundamental advantages of POMs, such as the diversity of molecular structures and large numbers of redox active sites, numerous efforts have been devoted to extending their application areas. Up to now, various strategies of assembling POM molecules into superstructures, supporting POMs on heterogeneous substrates, and POMs-derived metal compounds have been developed for synthesizing electrocatalysts. From a multidisciplinary perspective, the latest advances in creating POM-structured materials with a unique focus on their molecular fundamentals, electrocatalytic roles, and the recent breakthroughs of POMs and POM-derived electrocatalysts, are systematically summarized. Notably, this paper focuses on exposing the current states, essences, and mechanisms of how POM-structured materials influence their electrocatalytic activities and discloses the critical requirements for future developments. The future challenges, objectives, comparisons, and perspectives for creating POM-structured materials are also systematically discussed. It is anticipated that this review will offer a substantial impact on stimulating interdisciplinary efforts for the prosperities and widespread utilizations of POM-structured materials in electrocatalysis.

Different anion (NO3- and OAc-)-controlled construction of dysprosium clusters with different shapes

The complex hydrolysis process and strong uncertainty of self-assembly rules have led to the precise synthesis of lanthanide clusters still being in the "blind-box" stage and simplifying the self-assembly process and developing reliable regulation strategies have attracted widespread attention. Herein, different anions are used to induce the construction of a series of dysprosium clusters with different shapes and connections. When the selected anion is NO3-, it blocks the coordination of metal sites around the cluster through the terminal group coordination mode, thereby controlling the growth of the cluster. When NO3- was changed to OAc-, OAc- adopted a bridging mode to induce modular units to build dysprosium clusters through an annular growth mechanism. Specifically, we selected 2-amino-6-methoxybenzoic acid, 2-hydroxybenzaldehyde, and Dy(NO3)3·6H2O to react under solvothermal conditions to obtain a pentanuclear dysprosium cluster (1). The five Dy(III) ions in 1 are distributed in upper and lower planes and are formed by the tight connection of nitrogen and oxygen atoms, and μ3-OH- bridges on the ligand. Next, octa-nuclear dysprosium cluster (2) were obtained by only regulating ligand substituents. The eight Dy(III) ions in 2 are tightly connected through ligand oxygen atoms, μ2-OH-, and μ3-OH- bridges, forming an elliptical {Dy/O} cluster core. Furthermore, only by changing NO3- to OAc-, a wheel-shaped tetradeca-nuclear dysprosium cluster (3) was obtained. Cluster 3 is composed of OAc- bridged multiple template Dy3L3 units and pulling of these template units connected by an annular growth mechanism forms a wheel-shaped cluster. The angle of the coordination site on NO3- is ∠ONO = 115°, which leads to the further extension of the metal sites on the periphery of clusters 1 and 2 through the terminal group coordination mode, thereby regulating the structural connection of the clusters. However, the angle of the coordination site on OAc- is ∠OCO = 128°, and a slightly increased angle leads to the formation of a ring-shaped cluster 3 by connecting the template units through bridging. This is a rare example of the controllable construction of lanthanide clusters with different shapes induced by the regulation of different anions, which provides a new method for the precise construction of lanthanide clusters with special shapes.

High-nuclearity Luminescent Lanthanide Nanocages for Tumor Drug Delivery

There is an unmet need for easy-to-visualize drug carriers that can deliver therapeutic cargoes deep into solid tumors. Herein, we report the preparation of ultrasmall luminescent imine-based lanthanide nanocages, Eu60 and Tb60 (collectively Ln60 ), designed to encapsulate anticancer chemotherapeutics for tumor therapy. The as-prepared nanocages possess large cavities suitable for the encapsulation of doxorubicin (DOX), yielding DOX@Ln60 nanocages with diameters around 5 nm. DOX@Ln60 are efficiently internalized by breast cancer cells, allowing the cells to be visualized via the intrinsic luminescent property of Ln(III). Once internalized, the acidic intracellular microenvironment promotes imine bond cleavage and the release of the loaded DOX. DOX@Ln60 inhibits DNA replication and triggers tumor cell apoptosis. In a murine triple negative breast cancer (TNBC) model, DOX@Ln60 was found to inhibit tumor growth with negligible side effects on normal tissues. It proved more effective than various controls, including DOX and Ln60 . The present nanocages thus point the way to the development of precise nanomedicines for tumor imaging and therapy.

Tandem templating strategies facilitate the assembly of calix[8]arene-supported Ln18 clusters

Calix[n]arenes offer ideal chemical functionality through the polyphenolic lower rim to construct nano-sized coordination clusters with lanthanide (Ln) metal ions (e.g., NdIII10, GdIII8). However, the number of metal centers they can accommodate is still limited compared to that achievable with smaller ligands (e.g., GdIII140, GdIII104). Here, we exploit a combination of the "anion template strategy" and "templating ligands" to synthesise three highly symmetric (D3h, trigonal planar) LnIII18 (Ln = La, Nd, and Gd) systems, representing the largest calix[n]arene-based coordination clusters yet. The LnIII18 fragment is templated by a chloride anion located at the center of the cluster, wherefrom twelve μ3-OH- ligands bind 'internally' to the eighteen LnIII ions. 'Externally' the metallic skeleton is connected by p-tert-butylcalix[8]arene, oxo, chloro and carbonate ligands. The crystal packing in the lattice reveals large cylindrical channels of ∼26 Å in diameter, whose pore volume corresponds to ∼50% of the unit cell volume (using a 1.2 Å spherical probe radius). Magnetic measurements reveal the predominance of weak antiferromagnetic exchange in the Gd analog. Heat capacity data of GdIII18 reveal a high magnetic entropy with -ΔSm = 23.7 J K-1 kg-1, indicating potential for engineering magnetic refrigerant materials with calix[8]arenes.

A nested spin structure and single molecule magnet behaviour in an Fe8Dy12 heterometallic cyclic coordination cluster

The 20-nuclearity compound [Fe8Dy12(tea)8(teaH)12(NO3)12]·8MeCN (where teaH3 = triethanolamine) was synthesised and characterised through single crystal X-ray diffraction and magnetic measurements. The shape of the magnetic hysteresis in the microSQUID measurements was rationalised using the MAGELLAN program.

{GdIII7} and {GdIII14} Cluster Formation Based on a Rhodamine 6G Ligand with a Magnetocaloric Effect

Heptanuclear {GdIII7} (complex 1) and tetradecanuclear {GdIII14} (complex 2) were synthesized using the rhodamine 6G ligand HL (rhodamine 6G salicylaldehyde hydrazone) and characterized. Complex 1 has a rare disc-shaped structure, where the central Gd ion is connected to the six peripheral GdIII ions via CH3O-/μ3-OH- bridges. Complex 2 has an unexpected three-layer double sandwich structure with a rare μ6-O2- ion in the center of the cluster. Magnetic studies revealed that complex 1 exhibits a magnetic entropy change of 17.4 J kg-1 K-1 at 3 K and 5 T. On the other hand, complex 2 shows a higher magnetic entropy change of 22.3 J kg-1 K-1 at 2 K and 5 T.

Atomically accurate site-specific ligand tailoring of highly acid- and alkali-resistant Ti(iv)-based metallamacrocycle for enhanced CO2 photoreduction

Skillfully engineering surface ligands at specific sites within robust clusters presents both a formidable challenge and a captivating opportunity. Herein we unveil an unprecedented titanium-oxo cluster: a calix[8]arene-stabilized metallamacrocycle (Ti16L4), uniquely crafted through the fusion of four "core-shell" {Ti4@(TBC[8])(L)} subunits with four oxalate moieties. Notably, this cluster showcases an exceptional level of chemical stability, retaining its crystalline integrity even when immersed in highly concentrated acid (1 M HNO3) and alkali (20 M NaOH). The macrocycle's surface unveils four specific, customizable μ2-bridging sites, primed to accommodate diverse carboxylate ligands. This adaptability is highlighted through deliberate modifications achieved by alternating crystal soaking in alkali and carboxylic acid solutions. Furthermore, Ti16L4 macrocycles autonomously self-assemble into one-dimensional nanotubes, which subsequently organize into three distinct solid phases, contingent upon the specific nature of the four μ2-bridging ligands. Notably, the Ti16L4 exhibit a remarkable capacity for photocatalytic activity in selectively reducing CO2 to CO. Exploiting the macrocycle's modifiable shell yields a significant boost in performance, achieving an exceptional maximum CO release rate of 4.047 ± 0.243 mmol g-1 h-1. This study serves as a striking testament to the latent potential of precision-guided surface ligand manipulation within robust clusters, while also underpinning a platform for producing microporous materials endowed with a myriad of surface functionalities.

Magnetocaloric Properties in Rare-Earth-Based Metal-Organic Frameworks: Influence of Magnetic Density and Hydrostatic Pressure

Magnetic refrigeration based on the magnetocaloric effect (MCE) in metal-organic frameworks (MOF) is regarded as an attractive approach to create more sustainable cooling systems with higher efficiency than traditional ones. Here, we report a study of the MCE in a series of rare-earth-based MOFs. We have considered the selection of the rare-earth cation by investigating materials belonging to the α-rare-earth polymeric framework-4 (α-RPF-4) MOF family, synthesized with different rare-earth cations, and observed that paramagnetic moment and saturation magnetization play an important role in enhancing the magnetic entropy change ΔSM. The effect of structural parameters has also been considered by investigating three classes of metal-organic Gd materials built up from different types of inorganic secondary building units, including clusters (as in Gd-UiO-66), one-dimensional (as in α-RPF-4), and layered (as in Gd-LRH) conformations. Moreover, the analysis of the hydrostatic pressure influence reveals a significant increase in the -ΔSM and relative cooling power (RCP) with values between 4.3 and 16.3 and 121-509 J/kg. Specifically, the RCPmax found was ∼683 J/kg for Gd-UiO-66, which is higher than the one recently observed for Gd2SiO5 (649.5 J/kg). The present study demonstrates that the engineering of metal-organic framework systems based on high Gd densities may favor enhancing of magnetocaloric responses even at low pressures, thus promoting a new design strategy for efficient cooling devices.

Chiral lanthanide-silver(I) cluster-based metal-organic frameworks exhibiting solvent stability, and tunable photoluminescence

Due to the lack of effective synthetic strategies, the preparation of chemically stable chiral Ag(I) cluster-based materials for assembly remains challenging. Here, we have developed an approach to synthesize three pairs of chiral Ln-Ag(I) cluster-based metal-organic frameworks (MOFs) named l-LnAg5-3D (Ln = Gd for 1-L, Eu for 2-L, and Tb for 3-L) and d-LnAg5-3D (Ln = Gd for 1-D, Eu for 2-D, and Tb for 3-D) by employing a chiral Ag(I) cluster ({Ag5S6}) as the node and Ln3+ ion as the inorganic linker. Structural analysis revealed that the chiral ligands induced chirality through the entire structure, resulting in a chiral helix arrangement of the C3-symmetric chiral {Ag5S6} nodes and Ln3+ ions. These compounds showed high solvent stability in various polar organic solvents. The solid-state circular dichroism (CD) spectra of compounds l-LnAg5-3D and d-LnAg5-3D exhibited obvious mirror symmetrical peaks. The emission spectra in the solid state revealed that compound 1-L only exhibited the emission peak of {Ag5S6}, while compounds 2-L and 3-L exhibited overlapping peaks of Ln3+ and {Ag5S6} at different excitation wavelengths. This demonstrates the tunable photoluminescence from {Ag5S6} to Ln3+ by introducing different Ln3+ ions and manipulating the excitation wavelengths. The study underscores the enhanced stability of Ag(I) cluster-based MOFs achieved through the incorporation of Ln3+ ions and establishes chiral Ln-Ag(I) cluster-based MOFs as promising candidates for advanced materials with tunable photoluminescence.

Composition Control in Molecular Cluster-Aggregates: A Toolbox for Optical Output Tunability via Energy Transfer Pathways

Composition control is a powerful tool for obtaining high-performance lanthanide (Ln) luminescent materials with adjustable optical outputs. This strategy is well-established for hierarchically structured nanoparticles, but it is rarely applied to molecular compounds due to the limited number of metal centers within a single unit. In this work, we present a series of molecular cluster-aggregates (MCAs) with an icosanuclear core {Ln2Eu2Tb16} (Ln = Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er, Tm, and Yb) in which we explore composition control, akin to nanoparticles, to modulate the optical output. More specifically, we target to understand how the presence of a third LnIII doping ion would impact the well-known TbIII → EuIII energy transfer and the ratiometric optical thermometry performance based on the TbIII/EuIII pair. Photophysical properties at room and at varying temperatures were investigated. Based on experimental data and well-established intrinsic features, such as spin-orbit coupling strength and LnIII 4f energy levels' structure, we discuss the possible luminescent processes present in each MCA and provide insight into qualitative trends that can be rationally correlated throughout the series.

Russian Doll-like 3d-4f Cluster Wheels with Slow Relaxation of Magnetization

The solvothermal reactions of LnCl3·6H2O and MCl2·6H2O (M = Co, Ni) with 2,2'-diphenol (H2L1) and 5,7-dichloro-8-hydroxyquinoline (HL2) gave three 3d-4f heterometallic wheel-like nano-clusters [Ln7M6(L1)6(L2)6(µ3-OH)6(OCH3)6Cl(CH3CN)6]Cl2·xH2O (Ln = Dy, M = Co, x = 3 for 1; Ln = Dy, M = Ni, x = 0 for 2; Ln = Tb, M = Ni, x = 0 for 3) with similar cluster structure. The innermost Ln(III) ion is encapsulated in a planar Ln6 ring which is further embedded in a chair-conformation M6 ring, constructing a Russian doll-like 3d-4f cluster wheel Ln(III)⸦Ln6⸦M6. 2 and 3 show obvious slow magnetic relaxation behavior with negligible opening of the magnetic hysteresis loop. Such a Russian doll-like 3d-4f cluster wheel with the lanthanide disc isolated by transition metallo-ring is rarely reported.

Lanthanide molecular cluster-aggregates as the next generation of optical materials

In this perspective, we provide an overview of the recent achievements in luminescent lanthanide-based molecular cluster-aggregates (MCAs) and illustrate why MCAs can be seen as the next generation of highly efficient optical materials. MCAs are high nuclearity compounds composed of rigid multinuclear metal cores encapsulated by organic ligands. The combination of high nuclearity and molecular structure makes MCAs an ideal class of compounds that can unify the properties of traditional nanoparticles and small molecules. By bridging the gap between both domains, MCAs intrinsically retain unique features with tremendous impacts on their optical properties. Although homometallic luminescent MCAs have been extensively studied since the late 1990s, it was only recently that heterometallic luminescent MCAs were pioneered as tunable luminescent materials. These heterometallic systems have shown tremendous impacts in areas such as anti-counterfeiting materials, luminescent thermometry, and molecular upconversion, thus representing a new generation of lanthanide-based optical materials.

Accurate binding of porous aluminum molecular ring catalysts with the substrate

Metal molecular rings are a class of compounds with aesthetically pleasing symmetry and fundamentally useful properties. The reported work generally focuses on the ring center cavity, and there is little known about those on the ring waist. Herein, we report the discovery of porous aluminum molecular rings and their performance and contribution to the cyanosilylation reaction. We develop a facile ligand induced aggregation and solvent regulation strategy towards AlOC-58NC and AlOC-59NT with high purity, high yield (75% and 70%, respectively) and gram-level scale-up. These molecular rings exhibit a "two-tier" pore feature involving the general central cavity and newly observed equatorial semi-open cavities. AlOC-59NT with two types of one-dimensional channels showed good catalytic activity. The interaction of the aluminum molecular ring catalyst with the substrate has been crystallographically characterized and theoretically confirmed, showing a ring adaptability process that involves the capture and binding of the substrate. This work provides new ideas for the assembly of porous metal molecular rings and to understand the overall reaction pathway involving aldehydes and is expected to inspire the design of low-cost catalysts through structural modifications.

Atomically accurate structural tailoring of thiacalix[4]arene-protected copper(II)-based metallamacrocycles

Accurate manipulation of ligands at specific sites in robust clusters is attractive but difficult, especially for those ligands that coordinate in intricate binding patterns. By linking the shuttlecock-like {Cu₄(μ₄-Cl)TC4A} motif and the phenylphosphate (PhPO₃^2-) ligand, we elaborately design and synthesize two Cu(II)-thiacalix[4]arene metallamacrocycles (MMCs), namely Cu₁₂L₃ and Cu₁₆L₄, which have regular triangular and quadrilateral topologies, respectively. While keeping the core intact, the Cl^- and PhPO₃^2- in those two MMCs, which coordinated in a μ₄-bridging fashion, can be accurately substituted with salicylate ligands. Theoretical calculations have been carried out to reveal the effect of ligand tailoring on the electronic structure of clusters. Structural regulation can affect the catalytic activity of these clusters, which has been verified by using the clusters as catalysts for selective sulfide oxidation.

High-stability spherical lanthanide nanoclusters for magnetic resonance imaging

High-nuclear lanthanide clusters have shown great potential for the administration of high-dose mononuclear gadolinium chelates in magnetic resonance imaging (MRI). The development of high-nuclear lanthanide clusters with excellent solubility and high stability in water or solution has been challenging and is very important for expanding the performance of MRI. We used N-methylbenzimidazole-2-methanol (HL) and LnCl3·6H2O to synthesize two spherical lanthanide clusters, Ln32 (Ln = Ho, Ho32; and Ln = Gd, Gd32), which are highly stable in solution. The 24 ligands L- are all distributed on the periphery of Ln32 and tightly wrap the cluster core, ensuring that the cluster is stable. Notably, Ho32 can remain highly stable when bombarded with different ion source energies in HRESI-MS or immersed in an aqueous solution of different pH values for 24 h. The possible formation mechanism of Ho32 was proposed to be Ho(III), (L)- and H2O → Ho3(L)3/Ho3(L)4 → Ho4(L)4/Ho4(L)5 → Ho6(L)6/Ho6(L)7 → Ho16(L)19 → Ho28(L)15 → Ho32(L)24/Ho32(L)21/Ho32(L)23. To the best of our knowledge, this is the first study of the assembly mechanism of spherical high-nuclear lanthanide clusters. Spherical cluster Gd32, a form of highly aggregated Gd(III), exhibits a high longitudinal relaxation rate (1 T, r1 = 265.87 mM-1·s-1). More notably, compared with the clinically used commercial material Gd-DTPA, Gd32 has a clearer and higher-contrast T1-weighted MRI effect in mice bearing 4T1 tumors. This is the first time that high-nuclear lanthanide clusters with high water stability have been utilized for MRI. High-nuclear Gd clusters containing highly aggregated Gd(III) at the molecular level have higher imaging contrast than traditional Gd chelates; thus, using large doses of traditional gadolinium contrast agents can be avoided.

Boosting the sensitivity with time-gated luminescence thermometry using a nanosized molecular cluster aggregate

Luminescence thermometry with trivalent lanthanide ions is a promising avenue for contactless temperature probing. The area has been growing exponentially for the last two decades, and its viability has been successfully demonstrated in various research domains. However, moving from laboratory equipment to real-life applications remains a challenging task. One of the reasons is the possibility of a background luminescence from the probing device or probed environment. To tackle this issue, we elegantly incorporate a rarely explored thermometric approach called time-gated luminescence thermometry (TGLT). Furthermore, we demonstrate an enhanced relative sensitivity through this innovative approach and a path to move toward practical application.

Structural Evolution and Properties of Praseodymium Antimony Oxochlorides Based on a Chain-like Tertiary Building Unit

Unveiling the structural evolution of single-crystalline compounds based on certain building units may help greatly in guiding the design of complex structures. Herein, a series of praseodymium antimony oxohalide crystals have been isolated under solvothermal conditions via adjusting the solvents used, that is, [HN(CH2CH3)3][FeII(2,2′-bpy)3][Pr4Sb12O18Cl15]·EtOH (1) (2,2′-bpy = 2,2′-bipyridine), [HN(CH2CH3)3][FeII(2,2′-bpy)3]2[Pr4Sb12O18Cl14)2Cl]·N(CH2CH3)3·2H2O (2), and (H3O)[Pr4Sb12O18Cl12.5(TEOA)0.5]·2.5EtOH (3) (TEOA = mono-deprotonated triethanolamine anion). Single-crystal X-ray diffraction analysis revealed that all the three structures feature an anionic zig-zag chain of [Pr4Sb12O18Cl15−x]n as the tertiary building unit (TBU), which is formed by interconnections of praseodymium antimony oxochloride clusters (denoted as {Pr4Sb12}) as secondary building units. Interestingly, different arrangements or linkages of chain-like TBUs result in one-dimensional, two-dimensional layered, and three-dimensional structures of 1, 2, and 3, respectively, thus demonstrating clearly the structural evolution of metal oxohalide crystals. The title compounds have been characterized by elemental analysis, powder X-ray diffraction, thermogravimetric analysis, and UV-Vis spectroscopy, and the photodegradation for methyl blue in an aqueous solution of compound 1 has been preliminarily studied. This work offers a way to deeply understand the assembly process of intricate lanthanide-antimony(III) oxohalide structures at the atomic level.

Lanthanide Single-molecule Magnets: Synthetic Strategy, Structures, Properties and Recent Advances

Single-molecule magnets (SMMs) show wide potential applications in the field of ultrahigh-density storage materials, quantum computing, spintronics, and so on. Lanthanide (Ln) SMMs, as an important category of SMMs, open up a promising prospect due to their large magnetic moments and huge magnetic anisotropy. However, the construction of high performance for Ln SMMs remains an enormous challenge. Although remarkable advances are focused on the topic of Ln SMMs, the research on Ln SMMs with different nuclear numbers is still deficient. Therefore, this review summarizes the design strategies for the construction of Ln SMMs, as well as the metal skeleton types. Furthermore, we collect reported Ln SMMs with mononuclearity, dinuclearity, and multinuclearity (three or more Ln spin centers) and the SMM properties including energy barrier (U_eff ) and pre-exponential factor (τ₀ ) are described. Finally, Ln SMMs with low-nuclearity SMMs, especially for single-ion magnets (SIMs), are highlighted to understand the correlations between structures and magnetic behavior of the detail SMM properties are described. We expect the review can shed light on the future developments of high-performance Ln SMMs.

Two Windmill-Shaped Ln18 Nanoclusters Exhibiting High Magnetocaloric Effect and Luminescence

The self-assembly of the high-nuclearity Ln-exclusive nanoclusters is challenging but of significance due to its aesthetically pleasing architectures and far-reaching latent applications in magnetic cooling technologies. Herein, two novel high-nuclearity lanthanide nanoclusters were successfully synthesized under solvothermal conditions, formulated as {[Gd₁₈(IN)₂₀(HCOO)₈(μ₆-O)(μ₃-OH)₂₄(H₂O)₄]·4H₂O}_n and {[Eu₁₈(IN)₁₆(HCOO)₈(CH₃COO)₄(μ₆-O)(μ₃-OH)₂₄(H₂O)₄]·5H₂O}_n (abbreviated as Gd₁₈ and Eu₁₈, HIN = isonicotinic acid). Both of them possess novel and exquisite windmill-shaped cationic cores in the family of high-nuclearity Ln-exclusive nanoclusters. Remarkably, the adjacent second building units are interconnected into a three-dimensional (3D) metal-organic framework by IN^- ligands. As expected, the abundant existence of Gd^III ions endows Gd₁₈ with a favorable magnetic entropy change at 2.0 K for ΔH = 7.0 T (-ΔS_m^max = 40.0 J kg^-1 K^-1), and Eu₁₈ displays the typical luminescence of Eu^III ions.

Gradual Size Enlargement of Aluminum-Oxo Clusters and the Photochromic Properties

Metallic clusters, assembled by functional motifs, possess the attribute of regulating the properties by changing inorganic and organic components. In this work, a series of aluminum-oxo clusters, [Al₆O(dmp)₄(Hdmp)₂]·2ⁱPrOH [Al₆-1, H₃dmp = 2,2-bis(hydroxymethyl)propionic acid], [Al₆(H₂thmmg)₆]·2DMF·2H₂O [Al₆-2, H₅thmmg = N-tris(hydroxymethyl)methylglycine], [Al₈(OH)₄(NAP-OH)₁₂(MeO)₇(MeOH)]Cl·7MeCN·3MeOH (Al₈, HNAP-OH = 3-hydroxy-2-naphthoic acid), and [Al₁₀(NA)₁₀(MeO)₂₀] (Al₁₀, HNA = nicotinic acid), were obtained based on different carboxylic acids, realizing metallic ring size enlargement from 5.91 to 9.32 Å. They all exhibit good chemical stability. Importantly, the Al₈ cluster displays obvious photochromic behavior from pale yellow to orange yellow, originating from the generation of photoinduced radicals in the metal-assisted ligand-ligand electron transfer process of 3-hydroxy-2-naphthoic acid (HNAP-OH). This work enriches the metal ring cluster chemistry and reports the example of the aluminum-oxo cluster-based photochromic material, developing a novel system of photochromic materials.

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.

Construction of a Near-Infrared Luminescent 48-Metal Rectangular Zn(II)-Yb(III) Nanocluster with Carbonate Templates for the Dual-Emissive Detection of Rutin as a Medicinal Ingredient

An interesting 48-metal Zn(II)-Yb(III) nanocluster (1) with a size of about 1.3 × 2.8 × 3.1 nm was constructed by carbonate templates from a Schiff base ligand. It exhibits ligand-centered emission and near-infrared (NIR) luminescence of Yb(III), which are used in the dual-emissive detection of rutin (Rut) with high sensitivity even in the presence of other interferences. The response behavior can be expressed by the second-order equation I_980 nm/I_510 nm = A*[Rut]² + B*[Rut] + C, and the limits of detection to Rut for the emissions of 1 are 2.23 μM and 0.20 nM.

Anion-Manipulated Hydrolysis Process Assembles of Giant High-Nucleation Lanthanide-Oxo Cluster

Widespread concern has been raised over the synthesis of highly nucleated lanthanide clusters with special shapes and/or specific linkages. Construction of lanthanide clusters with specific shapes and/or linkages can be achieved by carefully regulating the hydrolysis of lanthanide metal ions and the resulting hydrolysis products. However, studies on the manipulation of lanthanide-ion hydrolysis to obtain giant lanthanide-oxo clusters have been few. In this study, we obtained a tetraicosa lanthanide cluster (3) by manipulating the hydrolysis of Dy(III) ions using an anion (OAc^-). As far as we know, cluster 3 has the highest nucleation among all lanthanide-oxo clusters reported. In 3, two triangular Dy₃O₄ are oriented in opposite directions to form the central connecting axis Dy₆(OH)₈, which is in turn connected to six Dy₃O₄ that are oriented in different directions. Meanwhile, a sample of a chiral trinuclear dysprosium cluster (1) was obtained in a mixed CH₃OH and CH₃CN solvent and by replacing the anion in the reaction to Cl^- ions. In this cluster, 1,3,4-thiadiazole-2,5-diamine (L²) is free on one side through π···π interactions and is parallel to the o-vanillin (L¹)^- ligand, thus resulting in a triangular arrangement. The arrangement of L² affects the end group coordination in the cluster 1 structure through hydrogen bonding and induces the cluster to exhibit chirality. When the reaction solvent was changed to CH₃OH, a sample of cluster 2, composed of two independent triangular Dy₃ that have different end group arrangements, was obtained. Magnetic analysis showed that clusters 1 and 3 both exhibit distinctive single-molecule magnetic properties under zero-magnetic-field conditions. This study thus provides a method for the creation of chiral high-nucleation clusters from achiral ligands and potentially paves the way for the synthesis of high-nucleation lanthanide clusters with unique forms.

Construction of a High Nuclear Gadolinium Cluster with Enhanced Magnetocaloric Effect through Structural Transition

Starting from a dinuclear complex {Gd₂(L)₂(NO₃)₄(H₂O)₂}·2(CH₃CN) (1) based on 2,6-dimethoxyphenol (HL), a nonanuclear cluster {Gd₉(L)₄(μ₄-OH)₂(μ₃-OH)₈(μ₂-OCH₃)₄(NO₃)₈ (H₂O)₈}(OH)·2H₂O (2) was obtained via modulating the amount of the ligand and base. Both of them have been structurally and magnetically characterized. Complex 1 decorates the Gd₂ core bridged by double μ₂-phenoxyl oxygen atoms and coordinated neutral CH₃CN molecules, while 2 features the Gd₉ core with a sandglass-like topology. Magnetic investigations reveal that the weaker antiferromagnetic interactions between adjacent metal ions exist in complex 2 than in 1, which is in agreement with the theoretical results. Meanwhile, the magnetocaloric effect with a maximum -ΔS _m value changes from 27.32 to 40.60 J kg^-1 K^-1 at 2 K and 7 T.

Synthesis, Structure, and Magnetic Properties of an Fe36 Dimethylarsinate Cluster: The Largest "Ferric Wheel"

The synthesis and characterization of a high-nuclearity Fe^III/O/arsinate cluster is reported within the salt [Fe₃₆O₁₂(OH)₆(O₂AsMe₂)₆₃(O₂CH)₃(H₂O)₆](NO₃)₁₂ (1). The compound was prepared from the reaction of Fe(NO₃)₃·9H₂O, dimethylarsinic acid (Me₂AsO₂H), and triethylamine in a 1:2:4 molar ratio in acetonitrile. The Fe₃₆ cation of 1 is an unprecedented structural type consisting of nine Fe₄ butterfly units of two types, three {Fe^III₄(μ₃-O)₂} units A, and six {Fe^III₄(μ₃-O)(μ₃-OH)} units B, linked by multiple bridging Me₂AsO₂^- groups into an Fe₃₆ triangular wheel/loop with C₃ crystallographic and D₃ virtual symmetry that looks like a guitar plectrum. The unusual structure has been rationalized on the basis of the different curvatures of units A and B, the presence of intra-Fe₃₆ hydrogen bonding, and the tendency of Me₂AsO₂^- groups to favor μ₃-bridging modes. The cations stack into supramolecular nanotubes parallel to the crystallographic c axis and contain badly disordered solvent and NO₃^- anions. The cation of 1 is the highest-nuclearity "ferric wheel" to date and also the highest-nuclearity Fe/O cluster of any structural type with a single contiguous Fe/O core. Variable-temperature direct-current magnetic susceptibility data and alternating-current in-phase magnetic susceptibility data indicate that the cation of 1 possesses an S = 0 ground state and dominant antiferromagnetic interactions. The Fe₂ pairwise J_i,j couplings were estimated by the combined use of a magnetostructural correlation for high-nuclearity Fe^III/oxo clusters and density functional theory calculations using broken-symmetry methods and the Green's function approach. The three methods gave satisfyingly similar J_i,j values and allowed the identification of spin-frustration effects and the resulting relative spin-vector alignments and thus rationalization of the S = 0 ground state of the cation.

Achieving stable photoluminescence by double thiacalix[4]arene-capping: the lanthanide-oxo cluster core matters

Luminescence stability is a critical consideration for applying phosphors in practical devices. In this work, we report two categories of double p-tert-butylthiacalix[4]arene (H₄TC4A) capped clusters that exhibit characteristic lanthanide luminescence. Specifically, {[Ln₄(μ₄-OH)(TC4A)₂(DMF)₆(CH₃OH)₃(HCOO)Cl₂]}·xCH₃OH (Ln = Eu (1), Tb (2); x = 0–1) with square-planar [Ln₄(μ₄-OH)] cluster cores and {[Ln₉(μ₅-OH)₂(μ₃-OH)₈(OCH₃) (TC4A)₂ (H₂O)₂₄Cl₉]}·xDMF (Ln = Gd (3), Tb (4), Dy (5); x = 2–6) with hourglass-like [Ln₉(μ₅-OH)₂(μ₃-OH)₈] cluster cores are synthesized and characterized. By comparing 2 and 4, we find that several critical luminescence properties (such as quantum efficiency and luminescence stabilities) depend directly on the cluster core structure. With the square-planar [Ln₄(μ₄-OH)] cluster cores, 2 demonstrates high quantum yield (∼65%) and excellent luminescence stability against moisture, high temperature, and UV-radiation. A white light-emitting diode (LED) with ultrahigh color quality is successfully fabricated by mixing 2 with commercial phosphors. These results imply that high quality phosphors might be achieved by exploiting the double thiacalix[4]arene-capping strategy, with an emphasis on the cluster core structure.

{Ln₄} cores outperform {Ln₉} cores in achieving stable photoluminescence from double thiacalix[4]arene-capped lanthanide-oxo clusters.

Self-assembly of octanuclear Ln(III)-based clusters: their large magnetocaloric effects and highly efficient conversion of CO2

The design and construction of high-nuclear lanthanide clusters with fascinating topology and functional properties have been an active area of research, however, the development of an effective approach for obtaining high-nuclear lanthanide clusters with multifunctional properties is still extremely difficult. Up to now, a systematic approach for guiding the further expansion of Ln(III)-based clusters showing good functional properties is lacking. Herein, we design and synthesize a polydentate Schiff base ligand (HL), which reacts with β-diketonate salts Ln(acac)₃·2H₂O, and a series of Ln₈ clusters [Ln₈(acac)₆(L)₂(μ₃-O)₆(μ₂-C₂H₅O)₄(μ₂-Hacac)₂]·2CH₃CN (Ln(III) = Gd (1), Dy (2), and Ho (3); HL = pyridine-2-carboxylic acid (5-hydroxymethyl-furan-2-ylmethylene)-hydrazide, Hacac = acetylacetone) have been successfully synthesized. Single-crystal X-ray diffraction studies reveal that clusters 1-3 are isostructural and can be viewed as a Ln₈ core bridged by eighteen μ₂-O atoms, six μ₃-O atoms and two μ₄-O atoms. Magnetic studies show that cluster 1-Gd8 displays a large magnetocaloric effect with -ΔS_m = 46.14 J kg^-1 K^-1 (T = 2.0 K and ΔH = 7.0 T); cluster 2-Dy8 exhibits single-molecule magnet behavior under zero-field conditions. It is worth mentioning that the -ΔS_m of cluster 1-Gd8 is larger than that of most reported polynuclear Gd(III)-based clusters; the 2-Dy8 cluster is one of the rare polynuclear Ln_n SMMs (n ≥ 8) under zero dc field. Importantly, these Ln(III)-based clusters (1-3) can catalyze the cycloaddition of CO₂ with epoxides with high efficiency under mild conditions; and cluster 1-Gd8 as a catalyst could be reused at least three times without obvious loss of catalytic performance.

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.

Gd(OH)F2: A Promising Cryogenic Magnetic Refrigerant

Magnetic refrigerants with a large magnetocaloric effect (MCE) in a wide temperature range and low magnetic ordering temperature (T_o) in the sub-kelvin temperature region are not only crucial for adiabatic demagnetization refrigeration but also open up a broader parameter space for the optimal design of adiabatic demagnetization refrigerators. However, such magnetic refrigerants are extremely rare because they require magnetic materials to simultaneously satisfy three conditions: low T_o, weak magnetic interaction, and high magnetic density. Here, we report the syntheses, heat capacities, and magnetic properties of Gd(OH)_3-xF_x (1: x = 1, 2: x ≈ 1.5, and 3: x = 2), demonstrating for the first time that the introduction of fluoride anions into antiferromagnetic Gd(OH)₃ can effectively regulate its T_o. Significantly, 3 not only has a T_o of 0.5 K but also exhibits a large MCE in the temperature range from 0.5 to 4 K, representing the best magnetic refrigerant reported to date in the temperature range of 0.5-4 K from the viewpoint of the MCE.

Phonon-assisted molecular upconversion in a holmium(III)-based molecular cluster-aggregate

Upconversion (UC) is a fascinating process in which higher energy photons can be emitted from excitation by lower energy photons. The current challenge remains in downscaling and effectively achieving upconversion with lanthanide ions at the molecular scale. Here, using a rationally designed molecular cluster-aggregate (MCA), we demonstrate for the first time Ho^III ion molecular upconversion. The synthesized MCA exhibits identifiable Ho^III green and red UC emissions with a uniquely enhanced red to green ratio as well as a conventional near-infrared (NIR) emission. A combined rigid spherical cluster core with reduced molecular vibrations, ideally matched donor and acceptor excited levels via a phonon-assisted mechanism, led to an upconversion quantum yield of 5.24 × 10^-6%.

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.

Giant Crown-Shaped Dy34 Nanocluster with High Acid-Base Stability Assembled by an out-to-in Growth Mechanism

Lanthanoid metal ions have large ionic radii, complex coordination modes, and easy distortion of coordination spheres, but the design and synthesis of high-nucleation lanthanoid clusters with high stability in solution (especially aqueous solution) are challenging. Herein, a diacylhydrazone ligand (H₂L¹) with multidentate chelating coordination sites was used to react with Dy(OAc)₃·4H₂O under solvothermal conditions to obtain an example of a 34-nucleus crown-shaped dysprosium cluster [Dy₃₄(L)₈(μ₂-OH)(μ₃-OH)₂₁(μ₃-O)₁₄(OAc)₃₁(OCH₃)₂(H₂O)₁₅](OAc)₃ (1). Structural analysis showed that the bisacylhydrazone ligand H₂L¹ with polydentate chelate coordination sites could rapidly capture Dy^III ions, thereby forming 34-nucleus crown-shaped dysprosium cluster 1 following the out-to-in growth mechanism. Cluster 1 remained stable after immersion in solutions with different pH values (3-14) for 24 h. To the best of the authors' knowledge, high-nucleation lanthanoid clusters with excellent strong acid and base stability and water stability are very rare. Meanwhile, high-resolution electrospray mass spectrometry molecular ion peaks produced by cluster 1 were captured, which proved to be stable also in organic solvents. Magnetic research showed that cluster 1 exhibited frequency-dependent behavior. This work provides a new idea for designing and synthesizing high-nucleation lanthanoid clusters with high stability.

Family of Nanoclusters, Ln33 (Ln = Sm/Eu) and Gd32, Exhibiting Magnetocaloric Effects and Fluorescence Sensing for MnO4. Inorg Chem 2022;61:8861-8869. [PMID: 35653200 DOI: 10.1021/acs.inorgchem.2c00898]

A family of nanoclusters, [Ln₃₃(EDTA)₁₂(OAc)₂(CO₃)₄(μ₃-OH)₃₆(μ₅-OH)₄(H₂O)₃₈]·OAc·xH₂O (x ≈ 50, Ln = Sm for 1; x ≈ 70, Ln = Eu for 2) and [Gd₃₂(EDTA)₁₂(OAc)₂(C₂O₄)(CO₃)₂(μ₃-OH)₃₆(μ₅-OH)₄(H₂O)₃₆]·x(H₂O) (x ≈ 70 for 3; H₄EDTA = ethylene diamine tetraacetic acid), was prepared through the assembly of repeating subunits under the action of an anion template. The analysis of the structures showed that compounds 1 and 2 containing 33 Ln³⁺ ions were isostructural, which were constructed by three kinds of subunits in the presence of CO₃^2- as an anion template, while compound 3 had a slightly different structure. Compound 3 containing 32 Gd³⁺ ions was formed by three types of subunits in the presence of CO₃^2- and C₂O₄^2- as a mixed anion template. The CO₃^2- anions came from the slow fixation of CO₂ in the air. Meanwhile, one kind of high-nuclearity lanthanide clusters showed high chemical stability. The quantum Monte Carlo (QMC) calculation suggested that weak antiferromagnetic interactions were dominant between Gd³⁺ ions in 3. Magnetocaloric studies showed that compound 3 had a large entropy change of 43.0 J kg^-1 K^-1 at 2 K and 7 T. Surprisingly, compound 2 showed excellent recognition and detection effects for permanganate in aqueous solvents based on the fluorescence quenching phenomenon.