Substituent Effect to Fine-Tune Energy Levels of Atom-Precise [MoOS3 ]2- Modified Copper(I) Thiolate Clusters Boosting Recyclable Photocatalysis.

The propulsion of photocatalytic hydrogen (H2 ) production is limited by the rational design and regulation of catalysts with precise structures and excellent activities. In this work, the [MoOS3 ]2- unit is introduced into the CuI clusters to form a series of atomically-precise MoVI -CuI bimetallic clusters of [Cu6 (MoOS3 )2 (C6 H5 (CH2 )S)2 (P(C6 H4 -R)3 )4 ] ⋅ xCH3 CN (R=H, CH3 , or F), which show high photocatalytic H2 evolution activities and excellent stability. By electron push-pull effects of the surface ligand, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of these MoVI -CuI clusters can be finely tuned, promoting the resultant visible-light-driven H2 evolution performance. Furthermore, MoVI -CuI clusters loaded onto the surface of magnetic Fe3 O4 carriers significantly reduced the loss of catalysts in the collection process, efficiently addressing the recycling issues of such small cluster-based catalyst. This work not only highlights a competitively universal approach on the design of high-efficiency cluster photocatalysts for energy conversion, but also makes it feasible to manipulate the catalytic performance of clusters through a rational substituent strategy.

Atom-Precise Modification of Silver(I) Thiolate Cluster by Shell Ligand Substitution: A New Approach to Generation of Cluster Functionality and Chirality.

To realize the molecular design of new functional silver(I) clusters, a new synthetic approach has been proposed, by which the weakly coordinating ligands NO3- in a Ag20 thiolate cluster precursor can be substituted by carboxylic ligands while keeping its inner core intact. By rational design, novel atom-precise carboxylic or amino acid protected 20-core Ag(I)-thiolate clusters have been demonstrated for the first time. The fluorescence and electrochemical activity of the postmodified Ag20 clusters can be modulated by alrestatin or ferrocenecarboxylic acid substitution. More strikingly, when chiral amino acids were used as postmodified ligands, CD-activity was observed for the Ag20 clusters, unveiling an efficient way to obtain atom-precise chiral silver(I) clusters.

Ni@NiO Nanowires on Nickel Foam Prepared via "Acid Hungry" Strategy: High Supercapacitor Performance and Robust Electrocatalysts for Water Splitting Reaction.

Ni/NiO core-shell nanowires on nickel foam (NF) are successfully synthesized using an "acid-hungry" strategy. The 3D electrode with large accessible active sites and improved conductivity, possesses an optimized ionic and electronic transport path during electrochemical processes. High areal capacitance of 1.65 F cm-2 is obtained at an ultrahigh current density of 100 mA cm-2 , which is 19.88 times higher than pristine NF. The direct growth of nanowires makes the present supercapacitor electrode robust for long-term cycling test. By virtue of the favorable hydrogen adsorption energies on Ni0 and OHads energy on NiO or NiOOH, the 3D electrode exhibits high performance in hydrogen evolution reaction with 146 mV at η10 mA cm-2 and Tafel value of 72 mV dec-1 , and oxygen evolution reaction with 382 mV at η10 mA cm-2 and Tafel value of 103 mV dec-1 in 1 m KOH. An electrolyzer using 3D electrodes as both anode and cathode can yield a current density of 10 mA cm-2 at 1.71 V, and possesses superior long-term stability to an electrolyzer consisting of Pt/C||Ir/C. The present work develops an effective and low-cost method for the large-scale fabrication of Ni/NiO core-shell nanowires on commercial NF, providing a promising candidate for supercapacitors, fuel cells, and electrocatalysis.

Smart Transformation of a Polyhedral Oligomeric Silsesquioxane Shell Controlled by Thiolate Silver(I) Nanocluster Core in Cluster@Clusters Dendrimers.

Using polyhedral oligomeric silsesquioxane (POSS) modified by a thiol group as a protected ligand, atom-precise multi-heteorocluster-based dendrimers Ag12 @POSS6 (1 a and 1 b) were assembled. Through the reactive -SH groups, six POSS shell ligands stabilize the central 12-core silver(I) cluster by diverse Ag-S interactions. When such Ag12 @POSS6 complex was stimulated by different solvents (acetone or tetrahydrofuran), the core Ag12 silver(I) cluster underwent reversible structural transformation between flattened cubo-octahedral (in 1 a) and normal cubo-octahedral (in 1 b); concomitantly shell POSS clusters rearranged from pseudo-octahedral to quasi-octahedral. Furthermore, the film matrix modified by 1 a or 1 b showed different hydrophobicity.

A Silver(I)-Estrogen Nanocluster: GSH Sensitivity and Targeting Suppression on HepG2 Cell.

A structure-determined silver nanocluster of [Ag10 (Eth)4 (CF3 COO)6 (CH3 OH)3 ]·3C-H3 OH (Eth = ethisterone) (1), is firstly demonstrated by self-assembly of silver salt and ethisterone. Due to the thiophilicity of silver(I) ions, complex 1 shows reactivity with glutathione (GSH) molecules in solution and induces the fluorescence quenching behavior. Thus, complex 1 can be used as a fluorescent sensor for GSH. In consideration of the higher level of GSH in cancerous cells, complex 1 presents significant tumor suppression reactivity toward the human hepatocellular carcinoma (HepG2) cells with IC50 value of 165 × 10-9 m. Especially, complex 1 displays 3.4-fold higher in vitro cytotoxicity to HepG2 cells than that of the normal CCC-HEL-1 cells, which makes complex 1 a potential targeting suppression agent for cancerous cells. The molecular design of complex 1 not only generates a new medicine-silver(I) cluster family, but also opens a new avenue to the targeting anticancer organosilver(I) materials.

Acid-Base-Triggered Structural Transformation of a Polyoxometalate Core Inside a Dodecahedrane-like Silver Thiolate Shell.

Self-assembly of metavanadate and organosilver(I) salts leads to a novel dodecahedrane-like [Ag30 ((t) BuS)20 ](10+) silver(I) thiolate nanocage that tightly wraps an unusual C2h polyoxovanadate anion. The polyoxovanadate core undergoes transformation to a D3d configuration upon acidification, and reverts back to its original C2h structure upon addition of base. Chromism was observed for the silver(I) thiolate cluster during the configurational change of the central polyoxovanadate core; the color of the solution changes reversibly from green to dark yellow. This work represents the first reported example of chromic polyoxometalate-templated silver(I) thiolate shells that respond to external acid-base stimuli. It also represents an important advance in providing crystallographic proof that structural transformations occur in a nanoscale core-shell cluster.

Thermochromic luminescent nest-like silver thiolate cluster.

A novel discrete open high-nuclearity nest-like silver thiolate cluster complex, [Ag33 S3 (StBu)16 (CF3 COO)9 (NO3 )(CH3 CN)2 ](NO3 ) (1), has been isolated with nitrate and S(2-) anions acting as structure-directing templates. Its similar nest-like structure has been assembled into an extended layer [Ag31 S3 (StBu)16 (NO3 )9 ]n (2) by adjustment of auxiliary ligand. More interestingly, both complexes exhibit temperature-dependent luminescence of high sensitivity with a large fluorescence enhancement (12-fold for 1, 21-fold for 2), which can be easily recognized by the naked-eye (dramatic red-shift Δ=104 nm for 1, larger Δ=113 nm for 2 at 77 K compared to those at 298 K). The correlation between luminescent thermochromism and temperature-dependent variation of the coordination modes of template NO3 (-) anion, Ag⋅⋅⋅S and Ag⋅⋅⋅Ag distances are also elucidated through variable-temperature single-crystal X-ray crystal structure (VT-SCXRD) analyses.

Low-level expression of purine bases in BALB/3T3 cells monitored by ultrasensitive graphene-based glass carbon electrode.

Using an ultrasensitive chemically reduced graphene oxide and ionic liquid modified glass carbon electrode (RGI-GCE), separated electrochemical signals of adenine and hypoxanthine in both human breast cancer (MCF-7) and mouse embryonic fibroblast (BALB/3T3) cells were observed. For the first time, low-level expression of purine bases in noncancerous BALB/3T3 cells can be electrochemically monitored. The metabolism of purine bases in carcinogen agent-contaminated BALB/3T3 cells was also investigated through the change of electrochemical signals ascribed to different purine bases, which opens a new electrochemical approach to the exploration of a low-level purine mechanism in noncancerous cells.

Enhanced catalysis of a vanadium-substituted Keggin-type polyoxomolybdate supported on the M3O4/C (M = Fe or Co) surface enables efficient and recyclable oxidation of HMF to DFF.

In the reaction of oxidizing 5-hydroxymethylfurfural (HMF), attaining high efficiency and selectivity in the conversion of HMF into DFF presents a challenge due to the possibility of forming multiple products. Polyoxometalates are considered highly active catalysts for HMF oxidation. However, the over-oxidation of products poses a challenge, leading to decreased purity and yield. In this work, metal-organic framework-derived Fe3O4/C and Co3O4/C were designed as carriers for the vanadium-substituted Keggin-type polyoxomolybdate H5PMo10V2O40·35H2O (PMo10V2). In this complex system, spinel oxides can effectively adsorb HMF molecules and cooperate with PMo10V2 to catalyze the aerobic oxidation of HMF. As a result, the as-prepared PMo10V2@Fe3O4/C and PMo10V2@Co3O4/C catalysts can achieve efficient conversion of HMF into DFF with almost 100% selectivity. Among them, PMo10V2@Fe3O4/C exhibits a higher conversion rate (99.1%) under milder reaction conditions (oxygen pressure of 0.8 MPa). Both catalysts exhibited exceptional stability and retained their activity and selectivity even after undergoing multiple cycles. Studies on mechanisms by in situ diffuse reflectance infrared Fourier transform spectroscopy and X-ray photoelectron spectroscopy revealed that the V5+ and Mo6+ in PMo10V2, together with the metal ions in the spinel oxides, act as active centers for the catalytic conversion of HMF. Therefore, it is proposed that PMo10V2 and M3O4/C (M = Fe, Co) cooperatively catalyze the transformation of HMF into DFF via a proton-coupled electron transfer mechanism. This study offers an innovative approach for designing highly selective and recyclable biomass oxidation catalysts.

Graphene-supported polyoxometalate entrapped in a MIL-88A network with highly efficient conversion of polysulfides in Li-S batteries.

It has been demonstrated that polyoxometalates (POMs) have strong anchoring abilities with efficient catalysis of lithium polysulfides (LiPSs). However, the severe aggregation that buries the effective active sites of POMs along with poor electrical conductivity limits the practical application of POMs in lithium sulfur batteries (LSBs). In our strategy, we utilized reduced graphene oxide (rGO) to support a POM catalyst entrapped in a MIL-88A(FeCo) network with a hollow shell skeleton as the sulfur host material. H4PW11VO40 (PW11V) with optimal vanadium atom implantation ensures the ruggedness and integrity of the hollow structure, which is conducive to achieving high sulfur loading as well as accommodating the volume change of the sulfur cathode during the charging and discharging process. Importantly, PW11V can capture polysulfides through firm chemical adsorption and accelerate redox reactions of LiPS conversion by effective electrochemical catalysis. Furthermore, the satisfactory electrical conductivity of rGO provides access for electrons to reach the interface of PW11V and polysulfides and trigger Li-S conversion reactions. Thus, the constructed PW11V-based sulfur cathode exhibited a superior specific capacity of 905 mA h g-1 after 100 cycles under 0.2 C and long cycling life with a capacity recession rate of 0.046% for each cycle upon 500 cycles under 3 C. This research reveals the effect of vanadium atom substitution of POMs on the cycling performance of a sulfur cathode and affords insight for developing high-performance LSBs.

Manipulation of the MoO2/MoSe2 Heterointerface Boosting High Rate and Durability for Sodium/Potassium Storage.

The main challenge for sodium/potassium ion storage is to find the suitable host materials to accommodate the larger-sized Na+/K+ and conquer the sluggish chemical kinetics. Herein, by selenation of polyoxometalate in electrospinning fiber, a novel MoO2/MoSe2 heterostructure embedded in one-dimensional (1D) N,P-doped carbon nanofiber (MoO2/MoSe2@NPC) is rationally constructed to show distinct enhancement of rate performance and cycle life for sodium ion batteries (SIBs) and potassium ion batteries (PIBs). The 1D skeleton of MoO2/MoSe2@NPC decreases the diffusion pathway of Na+/K+, and the doping of N/P heteroatoms in carbon fiber creates abundant active sites and provides good reachability for Na+/K+ transportation. MoSe2 nanosheets grow in the bulk phase of MoO2 via in situ local phase transformation to achieve effective and firm heterointerfaces. Especially, the exposure extent of heterointerfaces can be controlled by treatment temperature during the preparation process, and the optimized heterointerfaces result in an ideal synergic effect between MoO2 and MoSe2. DFT calculations confirm that the internal electric field in the heterogeneous interface guides the electron transfer from MoO2 to MoSe2, combined with strong adsorption capacity toward sodium/potassium, facilitating ion/electron transfer kinetics. It is confirmed that the MoO2/MoSe2@NPC anode for SIBs delivers 382 mA h g-1 under 0.1 A g-1 upon 200 cycles; meanwhile, a reversible capacity of 266 mA h g-1 is maintained even under 2 A g-1 after 2000 cycles. For PIBs, it can reach up to 216 mA h g-1 in the 200th cycle and still retain 125 mA h g-1 after 2000 cycles under 1 A g-1. This study opens up a new interface manipulation strategy for the design of anode materials to boost fast Na+/K+ storage kinetics.

A 20-core copper(I) nanocluster as electron-hole recombination inhibitor on TiO2 nanosheets for enhancing photocatalytic H2 evolution.

For the design of atom-precise copper nanoclusters, besides the exploration of their aesthetic cage-like architectures, their structural modulation and potential applications are being extensively explored. Herein, an atom-precise 20-core copper(I)-alkynyl nanocluster (UJN-Cu20) protected by ethinyloestradiol ligands issynthesized. By virtue of outer-shell hydroxyl groups, UJN-Cu20 could be uniformly modified on the surface of TiO2 nanosheets via hydrogen bonding interactions, thus forming an efficient nanocomposite photocatalyst for hydrogen evolution. By constructing a Z-scheme heterojunction, the photocatalytic hydrogen evolution activity of the nanocomposite (13 mmol g-1 h-1) significantly improved as compared to that of TiO2 nanosheets (0.4 mmol g-1 h-1). As a narrow bandgap cocatalyst, UJN-Cu20 is confirmed to effectively inhibit the electron-hole recombination on the surface of the TiO2 nanosheet, which provides a new concept for the design of copper cluster-assisted effective photocatalysts.

Polyoxometalate@MOF derived porous carbon-supported MoO2/MoS2 octahedra boosting high-rate lithium storage.

Structural stability and rapid charge-discharge capability of electrode materials are required for high performance lithium-ion batteries (LIBs). The materials derived from polyoxometalates (POMs) show special advantages in inhibiting capacity attenuation, and good dispersion or combination of POMs with metal-organic frameworks (MOFs) is an important method to obtain high activity anode composites for LIBs. In this study, a uniform MoO2/MoS2 heterostructure with surface supported carbon (C-MoO2/MoS2) was successfully fabricated from a [Cu2(BTC)4/3(H2O)2]6[H3PMo12O40] precursor, which showed not only the designed octahedral morphology but also fast charge transfer, long working life, and high rate performance. Superior reversible lithium storage capacity of 1047 mA h g-1 after 300 cycles was obtained at 1 A g-1. Even after 700 cycles at 5 A g-1, the discharge specific capacity of 646 mA h g-1 was maintained, and rate capability of 610 mA h g-1 could be achieved at 10 A g-1. The high capacitive contribution could be explained by the relatively large specific surface area of porous C-MoO2/MoS2, which was mainly caused by the supported carbon network and MoS2 nanosheets, resulting in fast lithiation/delithiation processes.

Pt-Substituted polyoxometalate modification on the surface of low-cost TiO2 with highly efficient H2 evolution performance.

In this study, Pt-substituted polyoxometalate was first modified on the surface of commercially available TiO2, forming an efficient photocatalyst with high reactivity for hydrogen evolution. During the photocatalytic process, Pt-polyoxometalates not only increase the mobility rate of electrons but also improve the separation efficiency of photoinduced electrons and holes. After photoreduction, the in situ generated Pt0 species are anchored on the surface of polyoxometalate anion, which prevents further agglomeration. Then, the in situ formed Pt0 species and polyoxometalates synergistically promote the efficiency of photoinduced electron transfer from TiO2 to the protons adsorbed on the Pt0 surface. Although the content of Pt0 in the nanocomposite is only 0.6%, the photocatalytic hydrogen production rate reaches 5.6 mmol g-1 h-1 and remains stable at 4.5 mmol g-1 h-1 after the continuous catalytic process. Due to the modification of TiO2 by Pt-substituted polyoxometalate, this nanocomposite represents a practical model that possesses highly efficient photoelectric conversion performance. The presented work not only extends the family of new TiO2-polyoxometalate-based materials but also takes a further step toward the practical application of commercial TiO2 in photocatalytic hydrogen production.

Stepwise Achievement of Circularly Polarized Luminescence on Atomically Precise Silver Clusters.

The weakly coordinated anionic nitrate ligands in a centrosymmetric Ag20 cluster are replaced in a stepwise manner by chiral amino acids and two achiral luminescent sulfonic-group-containing ligands while nearly maintaining the original silver(I) cage structure. This surface engineering enables the atomically precise Ag20 clusters to exhibit the high-efficiency synergetic effects of chirality and fluorescence, producing rare circularly polarized luminescence among the metal clusters with a large dissymmetry factor of (|glum|) ≈ 5 × 10-3. This rational approach using joint functional ligands further opens a new avenue to diverse multifunctional metal clusters for promising applications.

Acid-induced surface functionalization of polyoxometalate by enclosure in a polyhedral silver-alkynyl cage.

Surface functionalization of polyoxometalate anions with silver(I) tert-butylethynide in an organic solution medium has been achieved for the first time using an acid-induced facile approach. The generated neutral hybrid monomeric complexes [Ag(40)(C[triple bond]C(t)Bu)(22)(CF(3)COO)(12)(V(10)O(28))].4CH(3)OH (1) and [Ag(40)(C[triple bond]C(t)Bu)(20)(CF(3)COO)(12)(Mo(6)O(22))].2CH(3)OH (2) constitute members of a new silver(I)-polyoxometalate family in which the polyoxometalate anion is embedded in a polyhedral silver(I) cluster assembled by multiple argentophilic Ag...Ag interactions.

A disulfur ligand stabilization approach to construct a silver(i)-cluster-based porous framework as a sensitive SERS substrate.

An atomically-precise silver(i)-cluster-based three-dimensional (3D) framework (UJN-1) stabilized by a ditiocarb (diethyldithiocarbamate) ligand has been unveiled for the first time by self-assembly. UJN-1 is composed of both Ag9 clusters and Ag5 subunits, of which the Ag9 clusters are bonded with Ag5 subunits by sharing the ditiocarb ligand to form a microporous 3,4-connected topological framework. The chemically reduced nano-sized derivative of UJN-1 exhibits highly sensitive surface enhanced Raman scattering (SERS) towards 4-mercaptobenzoic acid (4-MBA) signal molecules, which is ascribed to the porosity as well as the distribution of abundant crystalline Ag0 active sites. This work sheds light on a new bottom-up approach to construct SERS-active silver(i)-cluster-based 3D materials by disulfur ligand stabilization.

Oxidase-like mimic of Ag@Ag3PO4 microcubes as a smart probe for ultrasensitive and selective Hg(2+) detection.

An oxidase-like mimic system based on facilely synthesized Ag@Ag3PO4 microcubes (Ag@Ag3PO4MCs) was designed and utilized to detect mercury ions with high selectivity and ultrasensitivity. Ag@Ag3PO4MCs with an average size of ca. 1.6 µm were synthesized by the reaction of [Ag(NH3)2](+) complex and Na2HPO4 and subsequent photoreduction under ultraviolet light. The as-prepared Ag@Ag3PO4MCs can effectively catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) and o-phenylenediamine (OPD) in the presence of dissolved oxygen in slightly acidic solution, exhibiting oxidase-like activities rather than peroxidase-like activity. Interestingly, the introduction of Ag nanoparticles (AgNPs) on the surfaces of Ag3PO4MCs can dramatically enhance the oxidase-like activities due to a synergistic effect between AgNPs and Ag3PO4MCs, as evidenced by the faster oxidation speed of TMB and OPD than that of native Ag3PO4MCs in the presence of dissolved oxygen. The enzyme kinetics can be well-explained by the Michaelis-Menten equation. As "poisoning" inhibitor, Hg(2+) ions can inhibit the enzyme reaction catalyzed by Ag3PO4MCs or Ag@Ag3PO4MCs. On the basis of this effect, a colorimetric Hg(2+) sensor was developed by the enzyme inhibition reaction of Ag3PO4MCs or Ag@Ag3PO4MCs. The excellent specific interaction of Hg-Ag or Hg(2+)-Ag(+) provides high selectivity for Hg(2+) over interfering metal ions. Meanwhile, the sensitivity of this sensor to Hg(2+) is extremely excellent with a limit of detection as low as 0.253 nM for Ag@Ag3PO4MCs. Considering the advantages of low detection limit, low cost, facile preparation, and visualization, the colorimetric Ag@Ag3PO4MCs sensor shows high promise for the testing of Hg(2+) in water samples.

A silver-alkynyl cluster encapsulating a fluorescent polyoxometalate core: enhanced emission and fluorescence modulation.

A new silver(I)-alkynyl cluster with a [Eu(W5O18)2](9-) polyoxoanionic core of [Ag42{Eu(W5O18)2}((t)BuC≡C)28Cl4] [OH]·H2O (1) has been designed and synthesized. The [Eu(W5O18)2](9-) polyoxoanion acts as a template to induce the formation of the surrounding 42-core Ag(I) cage. Due to the hydrophobic silver(I)-alkynyl shell, 1 features an unusual fluorescence enhancement as compared to the precursor of the [Eu(W5O18)2](9-) polyoxoanionic core. Interestingly, the silver ions in the shell silver(I)-alkynyl cage can only be reduced to silver atoms by irradiation with high energy UV light (2 kW). Upon high UV irradiation, fluorescence quenching of 1 has been observed. Moreover, the solution fluorescence of 1 can be modulated by addition of S(2-) ions into the system, which also leads to the fluorescence quenching phenomenon. The successful synthesis of 1 demonstrates a new route to the detection of high energy UV irradiation or S(2-) ions by elaborate design of fluorescence quenching of silver(I)-alkynyl clusters.

Self-assembly of an unprecedented polyoxomolybdate anion [Mo20O66]12- in a giant peanut-like 62-core silver-thiolate nanocluster.

A polyoxometalate-templated silver thiolate nanocluster, [Ag62(S(t)Bu)40(Mo20O66)(Mo6O19)3(CH3CN)2]·(CF3SO3)4 (1), has been isolated, in which a giant peanut-like silver(i)-thiolate cluster [Ag62(S(t)Bu)40](22+) encapsulates an unprecedented [Mo20O66](12-) polyoxoanion core. It opens a new approach for the synthesis of both elusive polyoxometalates and high-nuclearity silver(i)-thiolate nanoclusters.