Cluster-assembled Materials Research Articles

Au25 Cluster-Based Atomically Precise Coordination Frameworks and Emission Engineering through Lattice Symmetry.

The atomically precise metal nanoclusters (NCs) have attracted significant attention due to their superatomic behavior originating from the quantum confinement effect. This behavior makes these materials suitable for various photoluminescence-based applications, including chemical sensing, bioimaging, and phototherapy, owing to their intriguing optical properties. Especially, the manipulation of inter- or intracluster interaction through cluster-assembled materials (CAMs) presents significant pathways for modifying the photophysical properties of NCs. Herein, two distinct CAMs, Au25-Zn-Hex and Au25-Zn-Rod, were synthesized via forming a coordination bond between [Au25(p-HMBA)18]- (p-H2MBA = 4-mercaptobenzoic acid) and Zn2+. Au25-Zn-Rod exhibited a 6-fold higher luminescence intensity in the near-infrared region compared to Au25-Zn-Hex, attributed to synergistic inter- and intracluster interactions that induce exciton delocalization and structure rigidification at the atomic scale. This study highlights the potential of diverse lattice symmetries in cluster-based frameworks for tuning the photophysical properties, contributing to a deeper understanding of the structure-property relationship in Au NCs.

Assembly-inspired multiferroicity with nontrivial Chern insulating phase from exohedral metallofullerenes.

Fullerene-assembled low-dimensional materials have been experimentally realized in polymorphic forms and have attracted significant interest very recently. Here, we predict a two-dimensional (2D) honeycomb lattice material TM2(C60)3 (TM = Cr, Mo, and W) assembled from exohedral metallofullerene clusters TM(C60)3 that could exhibit planar triangular geometries. According to first-principles calculations combined with Monte Carlo simulations, we suggest that these 2D assembled materials exhibit various exotic physical properties, including ferromagnetism, ferroelectricity, and quantum anomalous Hall effect. Interestingly, mechanical strains could effectively tune their magnetic moments and switch the conducting spin channel of the Dirac bands at the Fermi level. Our work provides a new cluster-assembly design strategy toward cluster-assembled 2D materials based on fullerene characters.

Silver Cluster Assembled Materials: A Model-Driven Perspective on Recent Progress, with a Spotlight on Ag12 Cluster Assembly.

The exploration of individual nanoclusters is rapidly advancing, despite stability concerns. To address this challenge, the assembly of cluster nodes through linker molecules has been successfully implemented. However, the linking of the cluster nodes itself introduces a multitude of possibilities, especially when additional factors come into play. While this method proves effective in enhancing material stability, the specific reasons behind its success remain elusive. In our laboratory, we have undertaken extensive studies on Ag cluster-assembled materials. So, here our goal is to establish a model system that allows for the discernment of various factors, eliminating unnecessary complexities during the linking approach. So, we hope that the systematic discourse presented in here will contribute significantly to future endeavors, helping to set clear priorities, and provide solutions to concerns that arise when working with a model system.

Large-size gold–aluminum alloy cluster Al12Au60 stabilized by an encapsulating B12 icosahedron: a first-principles study

The investigation of novel clusters incorporating gold (Au) has attracted increasing attention due to their intriguing architecture and feasibility of experimental synthesis. In this study, a large-size gold–aluminum alloy cluster with icosahedral B12 as its core, specifically a B12@Al12Au60 cluster, is proposed and demonstrated to have remarkable stability as ascertained through first-principles calculations. The core–shell assembly, B12@Al12Au60, exhibiting I symmetry, is characterized by the incorporation of an icosahedral B12 motif within the outer shell of the Al12Au60 framework. By thorough analysis encompassing vibrational frequency and molecular dynamics simulations, the structural stability of the core–shell B12@Al12Au60 is investigated. The electronic characteristics are probed through adaptive natural density partitioning analysis, revealing the presence of 66 multi-center two-electron σ bonds distributed across the entirety of the core–shell configuration. Furthermore, scrutiny of distinct dimeric configurations composed of core–shell B12@Al12Au60 underscores their relative autonomy and potential prospects for applications within cluster-assembled materials.

Recent progress in atomically precise silver nanocluster-assembled materials.

In the dynamic landscape of nanotechnology, atomically precise silver nanoclusters (Ag NCs) have emerged as a novel and promising category of materials with their fascinating properties and enormous potential. However, recent research endeavors have surged towards stabilizing Ag-based NCs, leading to innovative strategies like connecting cluster nodes with organic linkers to construct hierarchical structures, thus forming Ag-based cluster-assembled materials (CAMs). This approach not only enhances structural stability, but also unveils unprecedented opportunities for CAMs, overcoming the limitations of individual Ag NCs. In this context, this review delves into the captivating realm of atomically precise nitrogen-based ligand bonded Ag(I)-based CAMs, providing insights into synthetic strategies, structure-property relationships, and diverse applications. We navigate the challenges and advancements in integrating Ag(I) cluster nodes, bound by argentophilic interactions, into highly connected periodic frameworks with different dimensionalities using nitrogen-based linkers. Despite the inherent diversity among cluster nodes, Ag(I) CAMs demonstrate promising potential in sensing, catalysis, bio-imaging, and device fabrication, which all are discussed in this review. Therefore, gaining insight into the silver nanocluster assembly process will offer valuable information, which can enlighten the readers on the design and advancement of Ag(I) CAMs for state-of-the-art applications.

On the variation of cluster core characteristics by an endohedral atom. Shape variation in 8-ce [EAu4(PPh3)4]2+ (E = N, P, As, Sb) clusters.

Atomically precise gold superatoms have attracted interest owing to their suitable use as building blocks for cluster-assembled materials, favoring ordered structures with advanced properties. In this sense, expanding their versatility is a relevant issue for controlling their properties and retaining a specific nuclearity. Interestingly, the reported structure for isoelectronic [Au4N(PPh3)4]+ and [Au4Sb(PPh3)4]+ clusters denotes two contrasting shapes featuring a tetrahedral and square pyramidal structure, respectively. Herein, we further explore the [Au4E(PPh3)4]+ (E = N, P, As, Sb) series in order to evaluate energetic and structural factors determining the overall shape. Our results show a favorable [Au4(PPh3)4]4+/E3- interaction energy, predicting particular patterns in their UV-vis spectrum. Thus, the use of dopant atoms is enabled to vary the core shape and, in turn, to modify the cluster properties, which serve as a structural control, in addition to ligand-based and size approaches.

The structure and application portfolio of intricately architected silver cluster-assembled materials.

Silver Cluster-Assembled Materials (SCAMs) represent a new frontier of crystalline extended solids hallmarked by their customizable structures, commendable stabilities, and unique physical/chemical properties. Since their discovery in 2017, the diversity of organic linkers has endowed SCAMs with ingenious architectures and the application scenario has expanded beyond photoluminescence sensing to environmental sustainability and biomedical applications. It is critically important to chronicle these recent key advances and review the progress of SCAMs that can enable translating the material discoveries into real implementation. Herein, we provide a succinct overview of the trajectory of SCAM research, with crucial insights into atomic-level structural correlations with the phenomena at the nanoscale and discuss the gaps and opportunities that are still open in addition to charting a roadmap for future research directions.

A silver cluster-assembled material as a matrix for enzyme immobilization towards a highly efficient biocatalyst.

Silver cluster-assembled materials (SCAMs) epitomize well-defined extended crystalline frameworks that combine the ingenious designability at the atomic/molecular level and high structural robustness. They have captivated the interest of the scientific fraternity because of their modular construction which enables to systematically tailor their functions, and their capacity to not only inherit the characteristics of component building units but also introduce their uniqueness in endowing the final material with extraordinary properties. Herein, we demonstrate the synthesis of a novel (3,6)-connected two-dimensional (2D) SCAM [Ag12(StBu)6(CF3COO)6(THIT)6]n (described as TUS 5, THIT = 2,4,6-tri(1H-imidazol-1-yl)-1,3,5-triazine) composed of Ag12 cluster nodes and tritopic imidazolyl linkers. We have leveraged, for the first time, this precisely architected extended SCAM structure as a support matrix for enzyme immobilization. The electrostatic attraction between the negatively charged amano lipase PS and positively charged TUS 5 as well as the surface hydrophobicity of TUS 5 catered to great binding of lipase onto the TUS 5 matrix, in addition to boosting the activity of lipase via interfacial activation. Capitalizing on the cooperative benefits of organic and inorganic support matrices wherein organic supports impart with cost-efficiency, biocompatibility, and improved enzyme stability and reusability and inorganic supports confer high thermal, mechanical and microbial resistance, we have utilized the immobilized lipase on TUS 5 SCAM (lipase@TUS 5) for the kinetic resolution of (R,S)-1-phenylethanol by transesterification reaction. Importantly, lipase@TUS 5 could attain appreciably higher conversion into (R)-1-phenylethyl acetate, besides featuring superior thermal stability, solvent tolerance and recyclability, over the native lipase.

Tuning the electronic structure of gold cluster-assembled materials by altering organophosphine ligands.

Superatomic clusters can be assembled to build bulk matter, where the individual characteristics are preserved. The main benefit of these materials over conventional bulk species is the capability to tailor their features by altering the physicochemical identities of individual clusters. Electronic properties of metal clusters can be modified by a protective shell of ligands that attach to the surface and make the whole nanoparticle soluble in organic or aqueous solvents. In the present work, we demonstrate that properly chosen ligands provide not only steric protection from aggregation but also tune the redox activity of metal clusters. We investigate the role of the ligands in electronic structure tunability and ligand-field splitting. Our first-principles calculations agree with the experiments, showing that phosphine-protected gold materials are small gap semiconductors. The obtained bandgaps strongly depend on the ligand used. Hence, using phosphine and organophosphine ligands should be feasible and promising while designing the novel superatom-based materials since the desired range of the bandgap might be achieved (by the proper choice of the ligand).

Design and Investigation of Superatoms for Redox Applications: First-Principles Studies.

A superatom is a cluster of atoms that acts like a single atom. Two main groups of superatoms are superalkalis and superhalogens, which mimic the chemistry of alkali and halogen atoms, respectively. The ionization energies of superalkalis are smaller than those of alkalis (<3.89 eV for cesium atom), and the electron affinities of superhalogens are larger than that of halogens (>3.61 eV for chlorine atom). Exploring new superalkali/superhalogen aims to provide reliable data and predictions of the use of such compounds as redox agents in the reduction/oxidation of counterpart systems, as well as the role they can play more generally in materials science. The low ionization energies of superalkalis make them candidates for catalysts for CO2 conversion into renewable fuels and value-added chemicals. The large electron affinity of superhalogens makes them strong oxidizing agents for bonding and removing toxic molecules from the environment. By using the superatoms as building blocks of cluster-assembled materials, we can achieve the functional features of atom-based materials (like conductivity or catalytic potential) while having more flexibility to achieve higher performance. This feature paper covers the issues of designing such compounds and demonstrates how modifications of the superatoms (superhalogens and superalkalis) allow for the tuning of the electronic structure and might be used to create unique functional materials. The designed superatoms can form stable perovskites for solar cells, electrolytes for Li-ion batteries of electric vehicles, superatomic solids, and semiconducting materials. The designed superatoms and their redox potential evaluation could help experimentalists create new materials for use in fields such as energy storage and climate change.

Structures and stabilities of UPbn (n ≤ 18) clusters: A first-principles global optimization calculation

Endohedrally doped clusters have received much attention because they can act as superatoms and have great potential as the building blocks for cluster-assembled materials. We have carried out a comprehensive study based on the combination of the particle swarming optimization algorithm and the relativistic density functional theory, to obtain geometric structures and stabilities of lead (Pb) clusters doped with one uranium (U) atom. A gradual evolution pattern was observed with the increasing number of Pb atoms, from exohedrally doped structures to quasi-endohedral structures, and finally to endohedrally doped structures. At least 12 and 11 Pb atoms were necessary to encapsulate the U atom completely in the calculation without and with the spin-orbit coupling (SOC) effect respectively. The UPb16 cluster was represented as a highly stable endohedral cage structure with the U atom around its center. In addition, the crucial role of the SOC effect was emphasized. We hope that our findings will provide a fundamental understanding of actinide-doped lead clusters, which may be quite different from their light element analogues.

Two-Dimensional Robust Ferromagnetic Semiconductors via Assembly of Magnetic Superatoms [Fe6S8(CN)6]5.

Cluster-assembled materials are of considerable interest owing to their unique properties and extensive application prospects. Nevertheless, the majority of cluster-assembled materials developed to date are nonmagnetic, limiting their applications in spintronics. Thus, two-dimensional (2D) cluster-assembled sheets with intrinsic ferromagnetism are very desirable. Here, via first-principles calculations, utilizing the recently synthesized magnetic superatomic cluster [Fe6S8(CN)6]5- as a building block, we design a series of thermodynamically stable 2D nanosheets [NH4]3[Fe6S8(CN)6]TM (TM = Cr, Mn, Fe, Co) with robust ferromagnetic ordering (Curie temperatures (Tc) up to 130 K), medium band gaps (from 1.96 to 2.01 eV), and sizable magnetic anisotropy energy (up to 0.58 meV per unit cell). Among these nanosheets, the [NH4]3[Fe6S8(CN)6]Cr is a bipolar magnetic semiconductor, whereas the other three ([NH4]3[Fe6S8(CN)6]TM (TM = Mn, Fe, Co) are half semiconductors. Additionally, the electronic and magnetic properties of [NH4]3[Fe6S8(CN)6]TM (TM = Cr, Mn, Fe, Co) nanosheets can be easily modulated by electron and hole doping via simply controlling the number of ammonium counterions. Furthermore, the Curie temperatures of the 2D nanosheets can be improved to 225 and 327 K by choosing 4d/5d transition metals TM = Ru and Os, respectively.

Photo-Activated Circularly Polarized Luminescence Film Based on Aggregation-Induced Emission Copper(I) Cluster-Assembled Materials.

In this study, a pair of chiral copper(I) cluster-assembled materials (R/S-2) was prepared, exhibiting unique photo-response characteristics with a concentration-wavelength correlation property in DMSO solution. By the combination of R/S-2 with a polymethyl methacrylate (PMMA) matrix, the first photo-activated circularly polarized luminescence (CPL) film was developed, the CPL signal (glum =9×10-3 ) of which could be induced by UV light irradiation. Moreover, the film exhibited a reversible photo-response and extremely good fatigue resistance. Mechanism study revealed that the photo-response properties of the R/S-2 solution and film are attributed to the aggregation-induced emission (AIE) characteristics of R/S-2 and a photo-induced deoxygenation process. This study enriches the types of luminescent cluster-assembled molecules and provides a new strategy for the construction of metal cluster-based stimuli-responsive composite materials.

Endohedral group-14 clusters Au@X12 (X = Ge, Sn, Pb) and their anions: A first-principles study

Group-14 (Ge, Sn, Pb) clusters have attracted a lot of attention not only because of their unique structural models but also the outstanding building blocks as cluster-assembled materials. In this paper, we have systematically investigated the structure, chemical stability, electronic property, spherical aromaticity, and bonding of neutral Au@X12 (X = Ge, Sn, Pb) clusters and their anions using density-functional theory (DFT) calculations. It is found that the Au@Ge12 cluster displays bicapped pentagonal prism geometry, whereas Au@X12 (X = Sn, Pb) possess the perfect icosahedral geometry. Analysis of binding energy reveals that the species exhibit high chemical stabilities, especially for closed-shell anionic clusters, which contain 60 valence electrons. The hybridization between cage and Au enhances the chemical stability of clusters, while the enhanced stability can be explained by spherical aromaticity, confirmed by largely negative NICS values, of which eight π electrons satisfy 2(N + 1)2 counting rule, forming 2S22P6 set. The AdNDP analysis reveals that the delocalized chemical bonding is responsible for structural stabilization of clusters, e.g., eight delocalized 4c-2e σ-bonds on inner shell and five delocalized 4c-2e σ-bonds on outer shell. To summarize, the calculated results will provide further understanding for the design of novel building blocks as cluster-assembled nanomaterials.

A new two-dimensional luminescent Ag12 cluster-assembled material and its catalytic activity for reduction of hexacyanoferrate(III).

Silver cluster-assembled materials (SCAMs) have garnered significant interest as promising platforms for different functional explorations. Their atomically precise structures, intriguing chemical/physical properties, and remarkable luminescent capabilities make them highly appealing. However, the properties of these materials are primarily determined by their structural architecture, which is heavily influenced by the linker molecules used in their assembly. The choice of linker molecules plays a pivotal role in shaping the structural characteristics and ultimately determining the unique properties of SCAMs. To this end, the first SCAM with an intriguing (3,6)-connected kgd topology, [Ag12(StBu)6(CF3COO)6(TPBTC)6]n (termed TUS 3), TPBTC = benzene-1,3,5-tricarboxylic acid tris-pyridin-4-ylamide, has been synthesized by reticulating C6-symmetric Ag12 cluster cores with C3-symmetric tripodal pyridine linkers. Due to the structutural architecture of the linker molecule, TUS 3 posseses a luminescent porous framework structure where each two-dimensional (2D) layers are non-covalently linked with each other to form a three dimensional (3D) framework and ultimately offers uniaxial open channels. The compact mesoporous structural architecture not only gives the excellent surface area but also offers impressive stability of this material even in water medium. Taking advantage of these properties, TUS 3 shows brilliant catalytic activity in the reduction of hexacyanoferrate(III) using sodium borohydride in aqueous solutions.

Synthesis and luminescence properties of two silver cluster-assembled materials for selective Fe3+ sensing.

Silver cluster-assembled materials (SCAMs) are emerging light-emitting materials with molecular-level structural designability and unique photophysical properties. Nevertheless, the widespread application scope of these materials is severely curtailed by their dissimilar structural architecture upon immersing in different solvent media. In this work, we report the designed synthesis of two unprecedented (4.6)-connected three-dimensional (3D) luminescent SCAMs, [Ag12(StBu)6(CF3COO)6(TPEPE)6]n (denoted as TUS 1), TPEPE = 1,1,2,2-tetrakis(4-(pyridin-4-ylethynyl)phenyl)ethene and [Ag12(StBu)6(CF3COO)6(TPVPE)6]n (denoted as TUS 2), TPVPE = 1,1,2,2-tetrakis(4-((E)-2-(pyridin-4-yl)vinyl)phenyl)ethene, composed of an Ag12 cluster core connected by quadridentate pyridine linkers. Attributed to their exceptional fluorescence properties with absolute quantum yield (QY) up to 9.7% and excellent chemical stability in a wide range of solvent polarity, a highly sensitive assay for detecting Fe3+ in aqueous medium is developed with promising detection limits of 0.05 and 0.86 nM L-1 for TUS 1 and TUS 2 respectively, comparable to the standard. Furthermore, the competency of these materials to detect Fe3+ in real water samples reveals their potential application in environmental monitoring and assessment.

Silver cluster-assembled materials for label-free DNA detection.

Herein, we report two newly synthesized silver cluster-assembled materials (SCAMs), [Ag14(StBu)10(CF3COO)4(bpa)2]n (bpa = 1,2-bis(4-pyridyl)acetylene) and [Ag12(StBu)6(CF3COO)6(bpeb)3]n (bpeb = 1,4-bis(pyridin-4-ylethynyl)benzene) composed of Ag14 and Ag12 chalcogenolate cluster cores, respectively, bridged by acetylenic bispyridine linkers. The linker structures and electrostatic interaction between positively charged SCAMs and negatively charged DNA confer the SCAMs with the ability to suppress the high background fluorescence of single-stranded (ss) DNA probes with SYBR Green I nucleic acid stain, leading to high signal-to-noise ratio for label-free target DNA detection.

Phosphine-Protected Atomically Precise Silver–Gold Alloy Nanoclusters and Their Luminescent Superstructures

Superstructures made by assemblies of metal nanoclusters (NCs) have gained interest due to their atomic precision and exciting photophysical properties. Although there are some reports of cluster-assembled materials of NCs protected with thiols, the preparation of stable thiol-free analogs is largely unexplored due to the poor stability of such structures. Herein, we report the synthesis of phosphine-protected alloy NCs of silver with varying gold doping and superstructures of such systems. We show that alloying of phosphine-protected silver clusters with gold results in comparatively more stable clusters than weakly ligated hydride- and phosphine-coprotected silver clusters. Two new Ag–Au alloy cluster series, [Ag11–xAux(DPPB)5Cl5O2]2+, where x = 1–10 (Ag11–xAux in short), and [Ag15–xAux(DPPP)6Cl5]2+, where x = 1–6 (Ag15–xAux in short), have been synthesized using two different phosphines, 1,4-bis(diphenylphosphino)butane (DPPB) and 1,3-bis(diphenylphosphino)propane (DPPP), respectively. These alloy clusters possess aggregation-induced emission (AIE) property, which was unexplored till now for phosphine-protected silver clusters. A visibly nonluminescent methanol solution of these clusters showed strong red luminescence in the presence of water due to the formation of cluster-assembled spherical hollow superstructures without any template. A solvophobic effect along with π···π and C–H···π interactions in the ligand shell make the alloy NCs assemble compactly within the hollow spheres. The assembly makes them highly emitting due to the restriction of intramolecular motion. The emissive states of the alloy clusters show a many-fold increase in lifetime in the presence of water. Femtosecond transient absorption studies revealed the lifetime of the excited-state charge carriers in their monomeric and aggregated states. Apart from enriching the limited family of phosphine-protected silver alloy NCs, this work also provides a new strategy to build a controlled assembly of NCs with tailored luminescence. These materials could be new phosphors for applications in composites, sensors, thin films, and photonic materials.

Spatially Guided Assembly of Polyoxometalate Superlattices and Their Derivatives as High-Power Sodium-Ion Battery Anodes.

The use of polyoxometalate clusters (POMs) with multitudinous structures and surface properties as building blocks has sparked the development of cluster-assembled materials with many prospective applications. In comparison to classic molecules and assembly processes, control over the steric interactions and linkage of large POMs to achieve superlattices with multiple levels of organization remains a great challenge. This work presents a universal approach to modulate the spatial coordination behavior and configurations, and achieves a class of cluster superlattice architectures formed by linear alignment and two-dimensional arrangement of POM units. The formation mechanism is explained as a stepwise co-assembly pathway in which POMs can intervene and dictate a typical stripping-restacking combination mode with the lamellar mediator. These cluster superlattices with long-range POMs ordering impart distinct merits to their derivatives by sulfuration, for which we demonstrate the substantially promoted power and cycling life of these POM derivatives applied as sodium-ion battery anodes.

First-principles studies of the caged germanium clusters with gold doping and their adsorption on graphdiyne nanosheets

Graphdiyne (GDY) is a novel two-dimensional (2D) carbon material, and has the promising applications due to its unique structural features. A new series of GDY-based complexes was theoretically designed by adsorbing the AuGen (n = 14–16) clusters on GDY surface, namely AuGen-GDY complexes, and the geometries, electronic properties, and optical absorption spectra of these complexes were systematically studied using density functional theory calculations. Firstly, the stable structures of endohedral AuGen (n = 14–16) clusters were successfully found. The endohedral clusters possess high chemical stability, strong aromaticity, and delocalized 4c-2e and 5c-2e σ-bonds. Besides, the AuGen clusters can stably adsorb on triangular hole of conjugated GDY surface, by not only covalent bonds, but also weak interactions (e.g., van der Waals). Moreover, the addition of GDY reduced the HOMO-LUMO gaps and natural charges on Au atom, while GDY can effectively modulate the electronic structures of complexes. The optical absorption spectra of AuGen-GDY were discussed, and the type of the main electronic transitions is local excitation, which can be further confirmed by the hole-electron distributions. This study not only highlights the important of the adsorption of endohedral clusters on GDY surface, but also stimulates the further synthesis as potential candidate of novel GDY-based cluster-assembled materials.