Distortion Engineering: A Strategy to Modulate Molecular Upconversion with Molecular Cluster-Aggregates

The rational engineering of molecules is a powerful chemistry tool of pivotal importance in the fields of molecular magnetism and luminescence. Hence, systems that can be modulated via molecular engineering and composition control are expected to present extra versatility regarding the tunability of their properties. This is the case with molecular cluster aggregates (MCAs), high nuclearity molecular compounds. Herein, we demonstrate how the union of both strategies, namely, composition control and molecular engineering, can be employed to enhance molecular upconversion in MCAs. This was achieved by doping a {Gd8Er2Yb10} MCA with CeIII ions. By replacement of the optically silent GdIII ions with CeIII, the upconversion mechanism is modified due to CeIII-mediated cross-relaxation. In addition to this effect, we could also engineer the degree of metal site distortion due to the larger size of CeIII ions, relaxing the selection rules and impacting the upconversion quantum yield and luminescent thermometry. Opto-structural correlations demonstrate that the presented molecular engineering strategy can be used to enhance the performance of molecular upconverters.

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.

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.

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.

Ligand Induced Double-Chair Conformation Ln12 Nanoclusters Showing Multifunctional Magnetic and Proton Conductive Properties

Many methods have been utilized to adjust the size of superatomic metal nanoclusters, while tuning the geometric conformations of specific nanoclusters is rare. Here, we demonstrate that conformation variation can be realized by slightly modifying the ligand under maintaining the nuclei number of metal atoms. A series of novel "double-chair" conformation Ln₁₂ (Ln = Sm (1), Eu (2), Gd (3), Tb (4), and Dy (5)) clusters were generated by replacing 3-formylsalicylic acid with 2,3-dihydroxybenzoic acid in the Ln₁₂ nanocluster. Intriguingly, Dy₁₂ displays slow magnetic relaxation at low temperatures, while Gd₁₂ shows a large magnetocaloric effect (MCE) of 35.63 J kg^-1 K^-1 at 2 K for ΔH = 7 T. Additionally, the introduction of numerous coordination water molecules in these clusters enables Dy₁₂ and Gd₁₂ with high proton conductivity, namely, 2.13 × 10^-4 and 3.62 × 10^-4 S cm^-1 under 358 K and 95% RH humidity conditions.

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 Series of High-Nuclear Gadolinium Cluster Aggregates with a Magnetocaloric Effect Constructed through Two-Component Manipulation

The serialized expansion of high-nuclear clusters usually includes the controlled variable method and changes only a single variable. However, changing both variables will greatly increase the complexity of the reaction simultaneously. Therefore, the use of a two-component regulation reaction is rare. Herein, we used a diacylhydrazone ligand (H₄L¹) with multidentate chelating coordination sites for the reaction with Gd(NO₃)₃·6H₂O under solvothermal conditions to obtain an example of 16-nucleus disc-shaped cluster 1 with a brucite structure. The overall structure of cluster 1 can be regarded as an equilateral triangle, which is formed by three (L¹)^4- ions that can be regarded as "sides" and wrap the four-layer metal center Gd(III) ions. Notably, upon simultaneous regulation of the substituent of the ligand and the coordination anion, heptanuclear gadolinium cluster 2 was obtained. Cluster 2 can be regarded as a butterfly structure, which was formed by connecting two Gd₃L² molecules that were not in the same plane and through the central Gd(III) ion as an intersection. Moreover, hexanuclear gadolinium cluster 3 was obtained by changing the ligand substituent and adding an auxiliary ligand. Cluster 3 can be regarded as a chair structure, which was composed of two molecules of diacylhydrazone ligand (L²)^4- wrapping vacant cubane shared by four vertices. This study was the first to construct a series of high-nuclear gadolinium clusters through two-component regulation manipulation. The study of the magnetocaloric effect showed that the maximum values of -ΔS_m for clusters 1-3 were 34.05, 29.04, and 24.32 J kg^-1 K^-1, respectively, when T = 2 K and ΔH = 7 T.

A systematic study of halide-template effects in the assembly of lanthanide hydroxide cluster complexes with histidine

Controlled hydrolysis of lanthanide ions in the presence of histidine and halide templates of different sizes produced dodeca- and pentadecanuclear lanthanide hydroxide clusters.

Solvent-induced structural transformation from heptanuclear to decanuclear [Co–Ln] coordination clusters: trapping of unique counteranion and understanding of aggregation pathways

The MeCN solvent-induced transformations of heptanuclear LnIII3CoII2CoIII2⁺ cationic aggregates, associated with literature unknown Ln(iii)-pivalate-based counter anions, to decanuclear LnIII3CoII3/2CoIII4/5 clusters have been investigated.

Two pairs of chiral lanthanide–oxo clusters Ln14 induced by amino acid derivatives

Two pairs of chiral lanthanide–oxo clusters l-/d-Ln14 (Ln = Y/Dy) have been obtained under the action of anion template. The solid-state circular dichroism (CD) spectra of l-Y14/d-Y14 and l-Dy14/d-Dy14 displayed mirror symmetry effects.