Visible Light Induced Ag-Polyoxometalate Coassembly into Single-Cluster Nanowires

Mixed-Valence Coordination Strategy Creating Ordered Ternary Ultrasmall Homo-/Hetero-structures Driven by Lattice Match for Advanced Photochromism and Encryption Applications

Overcoming the challenges of integrating disparate components in nanoarchitectures, this study introduces a straightforward strategy based on a mixed-valence coordination approach, creating an ordered ternary heterostructure integrated with ultrasmall homojunction. This singular ordered homojunction-heterostructure unites ultrathin 1D rutile TiO2 nanowires (NWs) and ultrathin anatase TiO2 NWs with 0D Prussian Blue Analogs (PBAs) nanoparticles (NPs), all exhibiting crystallographic oriented alignment with each other, forming a ternary mesocrystals. Experimental and theoretical insights disclose that the complex interplay between these dissimilar components is governed by a spontaneous lattice match effect, which not only optimizes but also directs the charge transfer, thereby enhancing both efficiency and stability. It also allows for tailoring the valence states of Fe within the PBA, fine-tuning of the composite's photochromic properties, and introducing abundant defect structures that foster strong interaction with oxygen molecules, enabling controllable color-switching dynamics. Consequently, the FeII 1-xFeIII x-PBA/TiO2 exhibits an optimized ternary structure of R-TiO2/A-TiO2/PBA, demonstrating exceptional photoelectronic properties, significantly enhancing photochromism and secure encryption capabilities. These insights establish a solid foundation for engineering sophisticated complex-ordered nanoarchitectures, advancing sustainable energy and environmental technologies.

An [Ag3(dppy)2(NO3)3] n cluster polymer with narrowing fluorescence

Low-dimensional nanomaterials with lattice confinement, including those of nanoclusters (NCs), offer benefits for fluorescence narrowing. Compared to quantum dots of metal NCs, however, one-dimensional structures of such NCs challenge the single-crystal synthesis. Here, we report the synthesis of a novel [Ag3(dppy)2(NO3)3] n cluster polymer through the reduction of AgNO3 with NaBH4 in a dark environment. This cluster polymer incorporates the coordination and passivation of both diminished nitro groups (NO3) and diphenyl-2-pyridylphosphine (dppy) ligands. The weak Ag-Ag metallic bonds within this cluster polymer are governed by argentophilic interactions, with each Ag3 unit connected by a NO3 group. This cluster polymer exhibits photoluminescence with three emission bands at 308, 352, and 620 nm, aligned with the purple (308/352 nm) and red (620 nm) regions, respectively. We synthesized microfibers of this cluster polymer using reprecipitation, resulting in a fluorescence bandwidth reduction to approximately one-tenth in the microfiber samples relative to the diluted solution.

Stable Polyoxometalate-Based Metal-Organic Framework: Synthesis, Modification, and Catalytic Activity

Metal-organic frameworks (MOFs) with polyoxometalates (POMs) as the nodes usually feature a high stability. Those with available space and modifiable groups are expected to serve as a catalytic platform. In this work, a polyoxometalate-based metal-organic framework (POMOF)-bearing channel with a transversal surface of ca. 1.1 × 1.8 nm, [Ni(en)2]4H{[Ni6(tris)(en)3(SIP)1.5][B-α-PW9O34]}2·32H2O (1), was resulted by the collaboration of multiple ligands. The channel was lined with abundant amino groups that bonded with water molecules in it via hydrogen bonds. Compound 1 exhibited excellent thermal and chemical stabilities, which was confirmed by immersion experiments, in situ variable temperature powder X-ray diffraction, and reversible dehydration-hydration behavior. Pristine 1 showed remarkable activity in the hydrogen evolution reaction. According to the presence of amino groups in the channel, 1 was modified by Pd species. Resultantly, Pd was loaded into the channel successfully. The yielding material 1-Pd smoothly catalyzed the Suzuki-Miyaura coupling reactions.

CdWO4 Sub-1 nm Nanowires for Visible-Light CO2 Photoreduction

Quantum size effect usually causes energy level splitting and band broadening as material size decreases. However, this may change again by the surface adsorbents, doping and defects, which rarely attracts much attention. Herein, CdWO4 sub-1 nm nanowires (SNWs) with oleylamine adsorption, PO4 3--doping and oxygen defects are synthesized by combining Cd(CH3COO)2, H3PW12O40 (PW12) and oleylamine (abbreviated as PO4 3--CdWO4-X SNWs). Compared with bulk CdWO4, they exhibit unexpected absorption spectra (extended from 292 nm to 453 nm) and band gap (reduced from 4.25 eV to 2.74 eV), thus bringing remarkable visible-light CO2 photoreduction activity. Under 410 nm LED light irradiation, PO4 3--CdWO4-40 SNWs exhibit the highest photocatalytic performance with a CO2-to-CO generation rate of 1685 μmol g-1 h-1. Density functional theory (DFT) calculations demonstrate the adsorbed oleylamine raises the valence band and enhances the adsorption of reaction substrate and intermediates, thus decreasing their reduction energy barriers. Furthermore, PO4 3--doping and oxygen defects will generate defect energy band below the conduction band of PO4 3--CdWO4-40 SNWs, resulting in remarkable visible light absorption and superior photocatalytic CO2 reduction performance. This work highlights the significant impacts of surface adsorbents, doping and defects on the physicochemical and catalytic properties of sub-nano materials.

Polyoxometalate superlattices derived bimetallic sulfides to accelerate acidic and alkaline hydrogen evolution reaction

Over the years, polyoxometalates (POMs) have been advocated as one of the most promising classes of molecular preassembly platform for the fabrication of highly efficient metal sulfide electrocatalysts. However, designing POMs-derived metal sulfides with high intrinsic activity, good site accessibility and structural stability for both acidic and alkaline hydrogen evolution reaction (HER) remains a great challenge because of the self-aggregation and random distribution of traditional POM precursors. Herein, we have designed a bimetallic sulfide eventually encapsulated by C3N4 walls (CoMoS@CN) for efficient HER based on a simple hydrothermal and subsequent high-temperature vulcanization using the well-designed POM superlattice assembly as precursor. The organized superlattice structure with long-range ordered arrangements of POM units provide chance to prevent the agglomeration of metal sites. The in-situ formed exterior C3N4 protective wall can accelerate the electron transfer and protect catalyst from chemical corrosion in different electrolyte. The merits combining with a large specific surface area enable CoMoS@CN with remarked HER performance of low overpotentials of 164 and 95 mV at 10 mA cm-2 in acidic and alkaline conditions. Such results are better than that of p-CoMoS@CN synthesized by pyrolysis of the corresponding physical mixtures and other comparative single metal sulfides.

Interfacial Charge Transfer in One-Dimensional AgBr Encapsulated inside Single-Walled Carbon Nanotube Heterostructures

The advent of one-dimensional van der Waals heterostructure (1D vdWH) nanomaterials has provided valuable opportunities for the advancement of electronic or optical devices, as well as for exploring various condensed matter phenomena. Electron transfer is a fundamental process in host-guest interactions, significantly influencing nanoscale physicochemical processes. Elucidating the mechanism by which the host influences the electronic structure of the guest is essential for elucidating these interactions. This study reports the successful synthesis of a material system consisting of precisely resolved AgBr nanowires encapsulated within single-walled carbon nanotubes (SWCNTs) that has been successfully synthesized and utilized to investigate the intrinsic electron transfer across 1D vdWHs. Cyclic voltammetry (CV) was employed to investigate the 1D vdWH interaction between AgBr and SWCNTs, which provided a more intuitive and accurate characterization of the charge transfer from SWCNTs to AgBr. Furthermore, Kelvin probe force microscopy showed a 149 mV reduction in the average surface potential of carbon nanotubes after AgBr filling, supporting the efficacy of CV in probing electron dynamics in 1D vdWHs. Finally, theoretical calculations indicated a charge transfer of 0.11 e- per simulation cell, reinforcing the effectiveness of CV in assessing the interactions within 1D vdWHs.

Atomically Precise Ternary Cluster: Polyoxometalate Cluster Sandwiched by Gold Clusters Protected by N-Heterocyclic Carbenes

Coinage metal (Au, Ag, Cu) cluster and polyoxometalate (POM) cluster represent two types of subnanometer "artificial atoms" with significant potential in catalysis, sensing, and nanomedicine. While composite clusters combining Ag/Cu clusters with POM have achieved considerable success, the assembly of gold clusters with POM is still lagging. Herein, we first designedly synthesized two cluster structural units: an Au3O cluster stabilized by diverse N-heterocyclic carbene (NHC) ligands and an amine-terminated POM linker. The subsequent reaction involved amine substitution in the POM linker for the central O atom in the Au3O cluster, resulting in the first ternary composite cluster-a POM cluster sandwiched by two Au clusters protected by NHCs. Single-crystal X-ray diffraction and other characteristic methods characterized their atomically precise structures. Furthermore, altering the NHC ligands decreased the number of gold atoms in the sandwich structures, accompanying the different protonated degrees of amine ligand in the terminal end of the POM linker. These composite clusters showed excellent performances in catalytic H2O2 conversion through the synergistic effect between gold clusters and POM clusters. This work opens a new avenue to functional composite metal clusters and would promote their enhanced catalysis applications through intercluster synergistic interactions within composite systems.

Integrating Polyoxometalates and Silver Clusters into Atomically Precise Molecular Heterojunction

The Ag cluster-POM assemblies have been shown to possess interesting and potentially useful properties. However, there is no precedent example of atomically precise Ag cluster-POM assemblies showing heterojunction effects in photocatalysis. Herein, the synthesis and total structure determination of the periodically distributed molecular heterojunction [Ag12(SCy)6(CH3CN)12(PW12O40)]n (Ag12-PW12) are reported. The assembly of Ag/W clusters into 3D network can endow the resulting binary structure with an aesthetic topology and unique physicochemical properties. More remarkably, the incorporation of Ag12 cluster with PW12 can efficiently facilitate the separation of photogenerated electrons and holes, thus significantly promoting the catalytic efficiency in selective oxidation of sulfides. The Ag12-PW12 heterojunction can be recovered and reused five times with no drastic change in the catalytic performance. This research is expected to assist in the rational design of cluster-based heterojunction catalysts. The increase of catalytic activity of the Ag12-PW12 assembly in comparison with the unassembled Ag12 and PW12 clusters is attributed to the synergistic effect of Ag12 and PW12 clusters, offering the splendid opportunity for deciphering structure-reactivity relationship of heterostructure-coupled photosystem.

Sub-1 nm Materials Chemistry: Challenges and Prospects

Subnanometer materials (SNMs) refer to nanomaterials with a feature size close to 1 nm, similar to the diameter of a single polymer, DNA strand, and a single cluster/unit cell. The growth and assembly of subnanometer building blocks can be controlled by interactions at atomic levels, representing the limit for the precise manipulation of materials. The size, geometry, and flexibility of 1D SNMs inorganic backbones are similar to the polymer chains, bringing excellent gelability, adhesiveness, and processability different from inorganic nanocrystals. The ultrahigh surface atom ratio of SNMs results in significantly increased surface energy, leading to significant rearrangement of surface atoms. Unconventional phases, immiscible metal alloys, and high entropy materials with few atomic layers can be stabilized, and the spontaneous twisting of SNMs may induce the intrinsic structural chirality. Electron delocalization may also emerge at the subnanoscale, giving rise to the significantly enhanced catalytic activity. In this perspective, we summarized recent progress on SNMs, including their synthesis, polymer-like properties, metastable phases, structural chirality, and catalytic properties, toward energy conversion. As a critical size region in nanoscience, the development of functional SNMs may fuse the boundary of inorganic materials and polymers and conduce to the precise manufacturing of materials at atomic levels.

Ag+-Induced Assembly of Pt Clusters for Photocatalytic Hydrogen Production

Cluster-assembled nanowires provide a unique strategy for the preparation of high-performance nanostructures. However, existing preparations are limited by complex processes and harsh reaction conditions. Here, Ag+ ions were utilized as a novel structure-directing agent to generate the self-assembly of Pt clusters to form ultrafine nanowires with a diameter of less than 5 nm. Electrospray ionization mass spectrometry (ESI-MS) and extended X-ray absorption fine structure (EXAFS) characterizations demonstrated that every Ag+ bridged two [Pt3(CO)3(μ2-CO)3]n2- clusters through coordination and formed a sandwich-like structure of [Pt3(CO)3(μ2-CO)3]nAg[Pt3(CO)3(μ2-CO)3]m3-. As a result, multiple sandwich-like structures of [Pt3(CO)3(μ2-CO)3]nAg[Pt3(CO)3(μ2-CO)3]m3- were established by Ag+ to form Pt nanowire superstructures {[Pt3(CO)6]nAg[Pt3(CO)6]mAg[Pt3(CO)6]x}∞ (abbreviated as Ag-Pt NWS). Our results demonstrate that the Pt nanowire superstructures showed promising cocatalytic performance for photocatalytic H2 production with the involvement of Ag+, which promises a desirable way to develop advanced functional nanomaterials.

High-entropy-perovskite subnanowires for photoelectrocatalytic coupling of methane to acetic acid

The incorporation of multiple immiscible metals in high-entropy oxides can create the unconventional coordination environment of catalytic active sites, while the high formation temperature of high-entropy oxides results in bulk materials with low specific surface areas. Here we develop the high-entropy LaMnO3-type perovskite-polyoxometalate subnanowire heterostructures with periodically aligned high-entropy LaMnO3 oxides and polyoxometalate under a significantly reduced temperature of 100 oC, which is much lower than the temperature required by state-of-the-art calcination methods for synthesizing high-entropy oxides. The high-entropy LaMnO3-polyoxometalate subnanowires exhibit excellent catalytic activity for the photoelectrochemical coupling of methane into acetic acid under mild conditions (1 bar, 25 oC), with a high productivity (up to 4.45 mmol g‒1cat h‒1) and selectivity ( > 99%). Due to the electron delocalization at the subnanometer scale, the contiguous active sites of high-entropy LaMnO3 and polyoxometalate in the heterostructure can efficiently activate C - H bonds and stabilize the resulted *COOH intermediates, which benefits the in situ coupling of *CH3 and *COOH into acetic acid.

Interfacial-Assembly-Induced In Situ Transformation from Aligned 1D Nanowires to Quasi-2D Nanofilms

As the dimensionality of materials generally affects their characteristics, thin films composed of low-dimensional nanomaterials, such as nanowires (NWs) or nanoplates, are of great importance in modern engineering. Among various bottom-up film fabrication strategies, interfacial assembly of nanoscale building blocks holds great promise in constructing large-scale aligned thin films, leading to emergent or enhanced collective properties compared to individual building blocks. As for 1D nanostructures, the interfacial self-assembly causes the morphology orientation, effectively achieving anisotropic electrical, thermal, and optical conduction. However, issues such as defects between each nanoscale building block, crystal orientation, and homogeneity constrain the application of ordered films. The precise control of transdimensional synthesis and the formation mechanism from 1D to 2D are rarely reported. To meet this gap, we introduce an interfacial-assembly-induced interfacial synthesis strategy and successfully synthesize quasi-2D nanofilms via the oriented attachment of 1D NWs on the liquid interface. Theoretical sampling and simulation show that NWs on the liquid interface maintain their lowest interaction energy for the ordered crystal plane (110) orientation and then rearrange and attach to the quasi-2D nanofilm. This quasi-2D nanofilm shows enhanced electric conductivity and unique optical properties compared with its corresponding 1D geometry materials. Uncovering these growth pathways of the 1D-to-2D transition provides opportunities for future material design and synthesis at the interface.

Hydrogen-Bonded Mesoporous Frameworks with Tunable Pore Sizes and Architectures from Nanocluster Assembly Units

Construction of mesoporous frameworks by noncovalent bonding still remains a great challenge. Here, we report a micelle-directed nanocluster modular self-assembly approach to synthesize a novel type of two-dimensional (2-D) hydrogen-bonded mesoporous frameworks (HMFs) for the first time based on nanoscale cluster units (1.0-3.0 nm in size). In this 2-D structure, a mesoporous cluster plate with ∼100 nm in thickness and several micrometers in size can be stably formed into uniform hexagonal arrays. Meanwhile, such a porous plate consists of several (3-4) dozens of layers of ultrathin mesoporous cluster nanosheets. The size of the mesopores can be precisely controlled from 11.6 to 18.5 nm by utilizing the amphiphilic diblock copolymer micelles with tunable block lengths. Additionally, the pore configuration of the HMFs can be changed from spherical to cylindrical by manipulating the concentration of the micelles. As a general approach, various new HMFs have been achieved successfully via a modular self-assembly of nanoclusters with switchable configurations (nanoring, Keggin-type, and cubane-like) and components (titanium-oxo, polyoxometalate, and organometallic clusters). As a demonstration, the titanium-oxo cluster-based HMFs show efficient photocatalytic activity for hydrogen evolution (3.6 mmol g-1h-1), with a conversion rate about 2 times higher than that of the unassembled titanium-oxo clusters (1.5 mmol g-1h-1). This demonstrates that HMFs exhibited enhanced photocatalytic activity compared with unassembled titanium-oxo clusters units.

Tuning the Chirality Evolution in Achiral Subnanometer Systems by Judicious Control of Molecule Interactions

Chirality evolution from molecule levels to the nanoscale in an achiral system is a fundamental issue that remains undiscovered. Here, we report the assembly of polyoxometalate (POM) clusters into chiral subnanostructures in achiral systems by programmable single-molecule interactions. Driven by the competing binding of Ca2+ and surface ligands, POM assemblies would twist into helical nanobelts, nanorings, and nanotubes with tunable helicity. Chiral molecules can be used to differentiate the formation energies of chiral isomers and immobilize the homochiral isomer, where strong circular dichroism (CD) signals are obtained in both solutions and films. Chiral helical nanobelts can be used as circularly polarized light (CPL) photodetectors due to their distinct chiroptic responsivity for right and left CPL. By the fine-tuning of interactions at single-molecule levels, the morphology and CD spectra of helical assemblies can be precisely controlled, providing an atomic precision model for investigation of the structure-chirality relationship and chirality manipulation at the nanoscale.

Electron-Delocalization-Stabilized Photoelectrocatalytic Coupling of Methane by NiO-Polyoxometalate Sub-1 nm Heterostructures

The oxidative coupling of methane to C2 oxygenates merits great scientific and technological potential yet remains a challenge due to its inferior selectivity. Subnanomaterials (SNMs) with "p-n-p-n"-type heteroconstructions feature enhanced external field coupling properties and tunable electronic structures, serving as promising catalysts for the selective partial oxidation of methane. Here we develop NiO-polyoxometalate (POM) subnanocoils with a thickness of 1.8 nm, showing excellent catalytic activity toward photoelectrochemical coupling of methane into a C2 product under mild conditions (1 bar, 25 °C) with a notable productivity (up to 4.48 mmol gcat-1 h-1) and a high selectivity (>99%). Under photoelectrochemical coupling, C-H bonds can be activated by NiO, and the resulted *COOH intermediates are stabilized by the delocalized electrons in POM clusters. The contiguous active sites of NiO and POM at the molecular level allow the in situ coupling of *COOH into oxalate. This work points out an economic way for the oxidation of methane under mild conditions and may enlighten the design of functional SNMs from fundamental standpoints.

Microchemical environmental regulation of POMs@MIL-101(Cr) promote photocatalytic nitrogen to ammonia

The polyoxometalates (POMs) have been shown to be highly effective as reactive sites for photocatalytic nitrogen fixation reactions. However, the effect of POMs regulation on catalytic performance has not been reported yet. Herein, a series of composites (SiW₉M₃@MIL-101(Cr) (M = Fe, Co, V, Mo) and D-SiW₉Mo₃@MIL-101(Cr), D, Disordered) were obtained by regulating transition metal compositions and arrangement in the POMs. The ammonia production rate of SiW₉Mo₃@MIL-101(Cr) is much higher than that of other composites, reaching 185.67 μmol·h^-1·g^-1_cat in N₂ without sacrificial agents. The structural characterization of composites reveals that the increase of the electron cloud density of W atom in composites is the key to improve the photocatalytic performance. In this paper, the microchemical environment of POMs was regulated by transition metal doping method, thereby promoting the efficiency of photocatalytic ammonia synthesis for the composites, which provides new insights into the design of POM-based photocatalysts with high catalytic activity.

A Cut-to-Link Strategy for Cubane-Based Heterometallic Sulfide Clusters with Giant Third-Order Nonlinear Optical Response

Although the synthesis of low-dimensional metal sulfides by assembling cluster-based units is expected to promote the development of optical materials and models of enzyme active centers such as dinitrogenase, it is faced with limited assembly methodology. Herein we present a cut-to-link strategy to generate high-nuclearity assemblies, inspired by the formation of a Z-type dimer of the W-S-Cu analogues of P^N cluster through in situ release of active linkers. Four new compounds with structures based on the same {Tp*WS₃Cu₃} incomplete cubane-like units were obtained using varied combinations of mild reagents. Open-aperture Z-scan measurements demonstrated the highest-nuclearity complex has the largest nonlinear optical absorption coefficient among discrete cluster-based materials reported to date. This approach enables building high-nuclearity metal sulfide clusters through cluster-based building blocks and opens a way to the design and exploration of materials based on well-identified building blocks.

Precise Assembly of Polyoxometalates at Single-cluster Levels

Polyoxometalate (POM) clusters with atomic precision structures are promising candidates construct functional nanomaterials via self-assembly. Non-covalent interactions at molecular levels can govern the self-assembly of POM clusters, for which the precise control of POM-based assemblies can be realized at single-cluster levels. This mini-review focuses on the synthesis and properties of POM-based nanostructures, including amphiphilic POM assemblies and co-assemblies of POM clusters and other subnanometer building blocks. Several synthetic strategies have been developed for rational control of POM-based assemblies in terms of morphologies, compositions and properties. 1D subnanometer POM assemblies demonstrate remarkable enhanced mechanical properties due to the topological interactions between nanowires and surroundings. The in-depth understanding of POM-based assemblies may help in the design of functional nanomaterials in fundamental perspectives and applications.