[Ag115S34(SCH2C6H4t Bu)47(dpph)6]: synthesis, crystal structure and NMR investigations of a soluble silver chalcogenide nanocluster

Three in One: Three Different Molybdates Trapped in a Thiacalix[4]arene Protected Ag72 Nanocluster for Structural Transformation and Photothermal Conversion

Polyoxometalates (POMs) represent crucial intermediates in the formation of insoluble metal oxides from soluble metal ions, however, the rapid hydrolysis-condensation kinetics of MoVI or WVI makes the direct characterization of coexisted molecular species in a given medium extremely difficult. Silver nanoclusters have shown versatile capacity to encapsulate diverse POMs, which provides an alternative scene to appreciate landscape of POMs in atomic precision. Here, we report a thiacalix[4]arene protected silver nanocluster (Ag72b) that simultaneously encapsulates three kinds of molybdates (MoO4 2- , Mo6 O22 8- and Mo7 O25 8- ) in situ transformed from classic Lindqvist Mo6 O19 2- , providing more deep understanding on the structural diversity and condensation growth route of POMs in solution. Ag72b is the first silver nanocluster trapping so many kinds of molybdates, which in turn exert collective template effect to aggregate silver atoms into a nanocluster. The post-reaction of Ag72b with AgOAc or PhCOOAg produces a discrete Ag24 nanocluster (Ag24a) or an Ag28 nanocluster based 1D chain structure (Ag28a), respectively. Moreover, the post-synthesized Ag28a can be utilized as potential ignition material for further application. This work not only provides an important model for unlocking dynamic features of POMs at atom-precise level but also pioneers a promising approach to synthesize silver nanoclusters from known to unknown.

Thermally Hypsochromic or Bathochromic Emissions? The Silver Nuclei Does Matter

Structural modulation of core-shell silver nanoclusters from the inside is a huge challenge but of great importance in their syntheses. Herein, two silver nanoclusters [Ag₃ S₉ @Ag₄₂ ] (SD/Ag45b) and [Ag₉ S₉ @Ag₄₂ ] (SD/Ag51a) are isolated in the presence of different kinds of sulfonic acids. Uniquely, SD/Ag45b and SD/Ag51a show typical core-shell structures with the similar Ag₄₂ shell but different cores. The outer shell of 42 silver atoms comprises two Ag₃ trigons at two poles encircled by three equatorial distorted square cupolas (J₄ , Ag₁₂ ). The core in SD/Ag45b is a silver trigon ligated by nine S^2- ions (Ag₃ S₉ ), while a tricapped triangular prismatic Ag₉ also ligated by the same amount of S^2- ions (Ag₉ S₉ ) is observed in the inner core of SD/Ag51a. The electrospray ionization mass spectrometry (ESI-MS) indicates that the introduction of p-toluenesulfonic acid can realize the transformation from SD/Ag45b to Ag₅₁ . SD/Ag45b and SD/Ag51a show inverse luminescence thermochromic behaviors in the near-infrared (NIR) region, mainly dictated by the inner silver cores. This work not only realizes the synthesis of new silver nanoclusters by core modulation but also provides a prototype to get molecular-level insight into the correlation between structure and luminescence thermochromism.

Promoting Room Temperature Phosphorescence through Electron Transfer from Carbon Dots to Promethazine

Room temperature phosphorescence (RTP) as a fascinating phenomenon shows great potential toward multiple applications. Howbeit, it is challengeable to improve the phosphorescence efficiency of carbon dots (CDs) owing to their short lifetime. Herein, we proposed a facile, rapid, and gram-scale strategy to synthesize the cross-linked carbon dots (named N-CDs) with both bright blue fluorescence and green RTP emissions. To be specific, the polymer of polyethylenimine (PEI) served as the cross-linking agent and carbon source, during which process phosphoric acid accelerated the formation of the compact carbon core within 30 s. Subsequently, the cross-linked carbon dots with the rigid network formed a small singlet-triplet energy splitting (ΔE_ST) of 0.490 eV, thus exhibiting a long RTP lifetime of 429.880 ms while coated on the filter paper through the hydrogen bonds. Taking advantage of the double luminescence, we successfully achieved the dual-channel detection of promethazine by N-CDs. The fluorescence of N-CDs was obviously quenched by promethazine through the electron-transfer process, displaying the linear range from 0.4 to 8 mM. Significantly, the electron transfer (ET) from carbon dots to promethazine boosted their phosphorescence efficiency and prolonged the lifetime to 565.190 ms, and the enhanced phosphorescence facilitated the sensitive recognition of promethazine with the concentration range of 1-3000 μM. Meanwhile, the possible autofluorescence interference from biological samples could be avoided through this RTP assaying mode, providing the more accurate results. Also, their RTP and fluorescence endowed the current N-CDs with the ability of dual-signal painting and imaging. This strategy may broaden the new approaches to produce the long-lifetime and high-efficiency RTP material toward the sensing purpose.

Truly Monodisperse Molecular Nanoparticles of Cerium Dioxide of 2.4 nm dimensions: A {Ce100 O167 } Cluster

Ultra-small nanoparticles of CeO₂ obtained in molecular form, so-called molecular nanoparticles, have been limited to date to a family whose largest member is of nuclearity Ce₄₀ with a {Ce₄₀ O₅₈ } core atom count. Herein we report that a synthetic procedure has been developed to the cation [Ce₁₀₀ O₁₄₉ (OH)₁₈ (O₂ CPh)₆₀ (PhCO₂ H)₁₂ (H₂ O)₂₀ ]¹⁶⁺ , a member with a much higher Ce₁₀₀ nuclearity and a {Ce₁₀₀ O₁₆₇ } core that is more akin to the smallest ceria nanoparticles. Its crystal structure reveals it to possess a 2.4 nm size and high D_2d symmetry, and it has also allowed identification of core surface features including facet composition, the presence and location of Ce³⁺ and H⁺ (i.e. HO^- ) ions, and the binding modes of the ligand monolayer of benzoate, benzoic acid, and water ligands.

Thermochromism and piezochromism of an atomically precise high-nuclearity silver sulfide nanocluster

A novel high-nuclearity silver sulfide nanocluster [Ag₅₀S₇(SC₆H₄F)₃₆(dppp)₆]·4DMI, (hereafter abbreviated as 1⋅4DMI) was synthesised. Solvent-free crystals of 1 displayed a completely reversible narrowing and broadening of the optical band gap that was accompanied by visual thermochromism and piezochromism changeovers, when stimulated by varying temperatures between 113 and 413 K or by changing the pressure from 1 atm to 7.5 GPa.

Progress in controlling the synthesis of atomically precise silver nanoclusters

This short review was designed to summarize the advances in synthesis methods of silver nanoclusters.

A construction guide for high-nuclearity (≥50 metal atoms) coinage metal clusters at the nanoscale: bridging molecular precise constructs with the bulk material phase

Synthesis remains a major strength in chemistry and materials science and relies on the formation of new molecules and diverse forms of matter. The construction and identification of large molecules poses specific challenges and has historically lain in the realm of biological (organic)-type molecules with evolved synthesis methods to support such endeavours. But with the development of analytical tools such as X-ray crystallography, new synthesis methods toward large metal-based (inorganic) molecules and clusters have come to the fore, making it possible to accurately determine the precise distribution of hundreds of atoms in large clusters. In this review, we focus on different synthesis protocols used to form new metal clusters such as templating, alloying and size-focusing strategies. A specific focus is on group 11 metals (Cu, Ag, Au) as they currently predominate large metal cluster investigations and related Au and Ag bulk surface phenomena. This review focuses on metal clusters that have very high-nuclearity, i.e. with 50 or more metal centers within the isolated cluster. This size domain, it is believed, will become increasingly important for a variety of applications as these metal clusters are positioned at the interface between the molecular and bulk phases, whilst remaining a classic nanomaterial and retaining unique nano-sized properties.

tert-Butyl thiol and pyridine ligand co-protected 50-nuclei clusters: the effect of pyridines on Ag-SR bonds

Constructing silver(i)-thiolate clusters from simple building blocks usually involves elusive self-assembly processes and remains a long-standing challenge. In this work, we report 6 silver(i)-thiolate clusters protected by pyridines, namely, [Ag3(tBuS)2(Py)(NO3)]n (Py = pyridine) (1), [Ag10(tBuS)6(Py)6(CF3CO2)4]·3Py (2), [Ag12(iPrS)6(Py)8(NO3)6]·2H2O (3), Ag12(iPrS)6(Py)8(CF3CO2)6 (4), Ag12(iPrS)6(4-ap)6(NO3)6 (4-ap = 4-aminopyridine) (5), and [Ag50S13(tBuS)20(Py)12]·4BF4·4Py·4CH3OH·2H2O (6). Single-crystal X-ray crystallography analysis reveals that six clusters are constructed by four types of structural blocks, including the PyAg(tBuS)2 monomer, Py2Ag2(tBuS)2 dimer, Py3Ag3(tBuS)3 trimer and (4-ap)6Ag6(iPrS)6 hexamer. Notably, cluster 6 consists of a rhombic dodecahedron S@Ag14 kernel with 12 interstitial S2- atoms encapsulated by 8 μ4-tBuS- ligands, as well as six unique butterfly-like (Py)2Ag6(tBuS)2 staple motifs composed of a Py2Ag2(tBuS)2 dimer and four silver ions. Moreover, it is found that pyridine ligands have important influence on the construction of silver thiolate clusters and their Ag-SR bond lengths.

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.

New protective ligands for atomically precise silver nanoclusters

Atomically precise silver nanoclusters (NCs) have emerged as a hot topic attracting immense research interest. Protecting ligands are needed for direct capping on cluster surfaces in order to prevent aggregation and to stabilize NCs. It has been demonstrated that protective ligands are critical to determining the sizes, structures and properties of silver NCs. The past decades have witnessed conventionally used organic ligands (thiolates/selenols, phosphines and alkynyls) and inorganic ligands (chalcogens and halogens) being extensively used to passivate NC surfaces. However, only in the most recent years have new-type protecting ligands beyond the conventional ones begun to be introduced in the protecting sphere of new functional silver NCs. The present Frontier article covers the most recent examples of some new protective agents for well-defined silver NCs. We describe four classes of novel silver NCs stabilized by newly-developed surface ligands, namely, nitrogen-donor organic ligands, oxygen-donor inorganic ligands, metalloligands and macrocyclic hosts, paying attention to the synthesis, structures and properties of these silver NCs. This Frontier article will hopefully attract more cluster scientists to explore more freshly ligated atomically precise silver NCs with novel structures and properties in the years ahead. The literature survey in this review is based on publications up to February 2020. Some suggestions for future directions in this field are also given.

Ag18(μ8-S)(p-TBBT)16(PPh3)8: symmetry breaking induced by the core to generate chirality

A chiral silver-sulfur nanocluster with a μ₈-S inside, Ag₁₈(μ₈-S)(p-TBBT)₁₆(PPh₃)₈, was successfully synthesized and characterized. This nanocluster is composed of a crown-like Ag₈S core and an Ag₁₀S₁₆P₈ meso-shell. The presence of the core induces symmetry breaking of the nanocluster from S₈ to C₄, and therefore endows the cluster with chirality.

Facile synthesis of silver alkynide cluster and coordination polymers using picolinic acid as a co-ligand

We describe five 1D-coordination polymers and two discrete silver clusters consisting of alkynides and picolinic carboxylates as co-ligands. In some cases, DMSO or EtOH further solvated the structural motifs. Utilising the sterically demanding tri-isopropylsilyl acetylene afforded a tridecanuclear cluster that possessed an unprecedented core with a silver center surrounded by six octahedrally arranged silver atoms.

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.

Controlling magnetism of Au133(TBBT)52 nanoclusters at single electron level and implication for nonmetal to metal transition

The [Au₁₃₃(SR)₅₂]^q nanocluster is discovered to possess one spin per particle when q = 0, but no unpaired electron when q = +1.

The transition from the discrete, excitonic state to the continuous, metallic state in thiolate-protected gold nanoclusters is of fundamental interest and has attracted significant efforts in recent research. Compared with optical and electronic transition behavior, the transition in magnetism from the atomic gold paramagnetism (Au 6s¹) to the band behavior is less studied. In this work, the magnetic properties of 1.7 nm [Au₁₃₃(TBBT)₅₂]⁰ nanoclusters (where TBBT = 4-tert-butylbenzenethiolate) with 81 nominal “valence electrons” are investigated by electron paramagnetic resonance (EPR) spectroscopy. Quantitative EPR analysis shows that each cluster possesses one unpaired electron (spin), indicating that the electrons fill into discrete orbitals instead of a continuous band, for that one electron in the band would give a much smaller magnetic moment. Therefore, [Au₁₃₃(TBBT)₅₂]⁰ possesses a nonmetallic electronic structure. Furthermore, we demonstrate that the unpaired spin can be removed by oxidizing [Au₁₃₃(TBBT)₅₂]⁰ to [Au₁₃₃(TBBT)₅₂]⁺ and the nanocluster transforms from paramagnetism to diamagnetism accordingly. The UV-vis absorption spectra remain the same in the process of single-electron loss or addition. Nuclear magnetic resonance (NMR) is applied to probe the charge and magnetic states of Au₁₃₃(TBBT)₅₂, and the chemical shifts of 52 surface TBBT ligands are found to be affected by the spin in the gold core. The NMR spectrum of Au₁₃₃(TBBT)₅₂ shows a 13-fold splitting with 4-fold degeneracy of 52 TBBT ligands, which are correlated to the quasi-D₂ symmetry of the ligand shell. Overall, this work provides important insights into the electronic structure of Au₁₃₃(TBBT)₅₂ by combining EPR, optical and NMR studies, which will pave the way for further understanding of the transition behavior in metal nanoclusters.

Distinct photophysical properties in atom-precise silver and copper nanocluster analogues

The synthesis of atom-precise analogues of homometallic nanoclusters remains a great challenge. Herein we report the first pair of atom-precise copper/silver-thiolate halide cluster analogues, namely [Cu17/Ag17I3S(C2B10H10S2)6(CH3CN)11] (Cu17 and Ag17), obtained by bottom-up self-assembly and complete-metal-exchange-induced cluster-to-cluster transformation, respectively. The differences in optical absorption and emission of these analogues were fully elucidated by experimental and theoretical methods.

From nano-balls to nano-bowls

Pentaphosphaferrocene [Cp*Fe(η5-P5)] in combination with Cu(i) halides is capable of a template-directed synthesis of fullerene-like spheres. Herein, we present the use of a triple decker complex as template that leads to the formation of unprecedented 'nano-bowls'. These spherical domes resemble the truncated fullerenes I h-C80 and represent a novel spherical arrangement in the chemistry of spherical molecules.

Formation of an NIR-emitting Ag34S3SBB20(CF3COO)62+ cluster from a hydride-protected silver cluster

Formation of an NIR emitting Ag₃₄S₃SBB₂₀(CF₃COO)₆²⁺ cluster.

Synthesis, structure, and condensed-phase reactivity of [Ag3(μ3-H)(μ3-BH4)LPh3](BF4) (LPh = bis(diphenylphosphino)amine) with CS2

Electrospray ionisation mass spectrometry (ESI-MS) was used to monitor the reaction of AgBF₄, bis(diphenylphosphino)amine (dppa = (Ph₂P)₂NH = L^Ph) and NaBH₄ in acetonitrile.

Small size yet big action: a simple sulfate anion templated a discrete 78-nuclearity silver sulfur nanocluster with a multishell structure

A discrete 78-nuclearity Ag nanocluster with a sulfate-centered multishell structure was obtained, indicating that simple anions can induce the formation of high-nuclearity Ag clusters.

Multi-ligand-directed synthesis of chiral silver nanoclusters

Engineering the surface ligands of metal nanoclusters is critical for tuning their sizes, structures and properties at the atomic level. Herein, we report the synthesis and total structure determination of [Ag₃₂(Dppm)₅(SAdm)₁₃Cl₈]³⁺ and [Ag₄₅(Dppm)₄(S-Bu^t)₁₆Br₁₂]³⁺ (where Dppm = bis(diphenyphosphino)methane, HSAdm = 1-adamantanethiol and HS-Bu^t = tert-butyl mercaptan). The compositions of these two silver nanoclusters are determined by single-crystal X-ray diffraction (SC-XRD) and X-ray photoelectron spectroscopy (XPS), respectively. Remarkably, the asymmetric distribution of the three types of ligands (thiolate, phosphine, and halogen) on the cluster surface is responsible for the chirality of the clusters. It is worth noting that these findings demonstrate the key principles of ligand-shell anchoring for the tri-ligand protected silver clusters. Our work will offer further insights into the synthesis of chiral metal clusters by tailoring the surface ligands.

Formation and Structural Diversity of Organo-Functionalized Tin-Silver Selenide Clusters

When reacting the organic functionalized tin selenide clusters [(SnR¹ )₃ Se₄ Cl] (A, R¹ =CMe₂ CH₂ C(O)Me) or [(SnR¹ )₄ Se₆ ] (B) with (SiMe₃ )₂ Se and [Ag(PPh₃ )₃ Cl] at -78 °C in CH₂ Cl₂ , a microcrystalline intermediate (compound 1) precipitates, which was investigated by magic angle spinning (MAS) NMR spectroscopy, powder X-ray diffraction (PXRD), energy dispersive X-ray (EDX) spectroscopy, and quantum chemistry calculations, to derive information about its composition and structure. Compound 1 re-dissolves under reorganization into the organo-functionalized Ag/Sn/Se cluster compound [Ag₆ (μ₆ -Se)(Ag₈ Se₁₂ ){(R¹ Sn)₂ Se₂ }₆ ] (2), or the mixed-valence cluster [(AgPPh₃ )₂ (Sn^II Cl)₂ Se₂ {(R¹ Sn^IV )₂ Se₂ }₂ ] (3), depending on the presence or the exclusion of daylight, respectively. The addition of N₂ H₄ ⋅H₂ O to a solution of 1 yields selectively [Ag₇ (μ₇ -Se)(Ag₇ Se₁₂ ){(R² Sn)₂ Se₂ }₆ ] (4, R² =CMe₂ CH₂ C(N₂ H₂ )Me), the Ag/Sn/Se core of which is isomeric to that of 2. 2-4 were characterized by X-ray diffraction. NMR spectroscopic studies on solutions of 1 indicate the co-existence of different species.