High‐Nuclear Organometallic Copper(I)–Alkynide Clusters: Thermochromic Near‐Infrared Luminescence and Solution Stability

Cu(CF₃COO)₂ reacts with tert‐butylacetylene (tBuC≡CH) in methanol in the presence of metallic copper powder to give two air‐stable clusters, [Cu^I₁₅(tBuC≡C)₁₀(CF₃COO)₅]?tBuC≡CH ( 1 ) and [Cu^I₁₆(tBuC≡C)₁₂(CF₃COO)₄(CH₃OH)₂] ( 2 ). The assembly process involves in situ comproportionation reaction between Cu²⁺ and Cu⁰ and the formation of two different clusters is controlled by reactants concentration. The clusters consist of Cu₁₅ and Cu₁₆ cores co‐stabilized by strong by σ‐ and π‐bonded tert‐butylethynide and CF₃COO^? (together with methanol molecule in 2 ). Their stabilities in solution were confirmed using electrospray ionization mass spectrometry in which the cluster core remains intact for 1 in chloroform and acetone, and for 2 in acetonitrile. Strong thermochromic luminescence in the near infrared (NIR) region was observed in the solid‐state. Of particular interest, the emission maximum of 1 is red‐shifted from 710 nm at 298 K to 793 nm at 93 K, along with a 17‐fold fluorescence enhancement. In contrast, 2 exhibits red shift from 298 to 123 K followed by blue shift from 123 to 93 K. The emission wavelength was correlated with the structural parameters using variable‐temperature X‐ray single‐crystal analyses. The rich cuprophilic interaction plays a significant role in the formation of ³LMCT (tBuC≡C→Cu_x) excited state mixed with cluster‐centered (³CC) characters, which can be considerably influenced by temperature, leading to thermochromic luminescence. The present work provides 1) a new synthetic protocol for the high‐nuclear Cu^I–alkynyl clusters; 2) a comprehensive insight into the mechanism of thermochromic luminescence; 3) unusual emissive materials with the characters of NIR and thermochromic luminescence simultaneously.     

Luminescent Thermochromism of 2D Coordination Polymers Based on Copper(I) Halides with 4‐Hydroxythiophenol

Solvothermal reactions between copper(I) halides and 4‐mercaptophenol give rise to the formation of three coordination polymers with general formula [Cu₃X(HT)₂]_n (X=Cl, 1 ; Br, 2 ; and I, 3 ). The structures of these coordination polymers have been determined by X‐ray diffraction at both room‐ and low temperature (110 K), showing a general shortening in Cu?S, Cu?X and Cu?Cu bond lengths at low temperatures. 1 and 2 are isostructural, consisting of layers in which the halogen ligands act as μ₃‐bridges joining two Cu1 and one Cu2 atoms whereas in 3 the iodine ligands is as μ₄‐mode but the layers are quasi‐isostructural with 1 or 2 . These compounds show a reversible thermochromic luminescence, with strong orange emission for 1 and 2 , but weaker for 3 at room temperature, whereas upon cooling at 77 K 1 and 2 show stronger yellow emission, and 3 displays stronger green emission. DFT calculations have been used to rationalize these observations. These results suggest a high potential for this novel and promising stimuli‐responsive materials.     

An All‐Alkynyl Protected 74‐Nuclei Silver(I)–Copper(I)‐Oxo Nanocluster: Oxo‐Induced Hierarchical Bimetal Aggregation and Anisotropic Surface Ligand Orientation

The hardness of oxo ions (O^2?) means that coinage‐metal (Cu, Ag, Au) clusters supported by oxo ions (O^2?) are rare. Herein, a novel μ₄‐oxo supported all‐alkynyl‐protected silver(I)–copper(I) nanocluster [Ag_74?xCu_xO₁₂(PhC≡C)₅₀] ( NC‐1 , avg. x=37.9) is characterized. NC‐1 is the highest nuclearity silver–copper heterometallic cluster and contains an unprecedented twelve interstitial μ₄‐oxo ions. The oxo ions originate from the reduction of nitrate ions by NaBH₄. The oxo ions induce the hierarchical aggregation of Cu^I and Ag^I ions in the cluster, forming the unique regioselective distribution of two different metal ions. The anisotropic ligand coverage on the surface is caused by the jigsaw‐puzzle‐like cluster packing incorporating rare intermolecular C?H???metal agostic interactions and solvent molecules. This work not only reveals a new category of high‐nuclearity coinage‐metal clusters but shows the special clustering effect of oxo ions in the assembly of coinage‐metal clusters.     

Superior Na‐Storage Performance of Low‐Temperature‐Synthesized Na3(VO1−xPO4)2F1+2x (0≤x≤1) Nanoparticles for Na‐Ion Batteries

Na‐ion batteries are becoming comparable to Li‐ion batteries because of their similar chemical characteristics and abundant sources of sodium. However, the materials production should be cost‐effective in order to meet the demand for large‐scale application. Here, a series of nanosized high‐performance cathode materials, Na₃(VO_1?xPO₄)₂F_1+2x (0≤x≤1), has been synthesized by a solvothermal low‐temperature (60–120 °C) strategy without the use of organic ligands or surfactants. The as‐synthesized Na₃(VOPO₄)₂F nanoparticles show the best Na‐storage performance reported so far in terms of both high rate capability (up to 10 C rate) and long cycle stability over 1200 cycles. To the best of our knowledge, the current developed synthetic strategy for Na₃(VO_1?xPO₄)₂F_1+2x is by far one of the least expensive and energy‐consuming methods, much superior to the conventional high‐temperature solid‐state method.     

Atomic‐Level Alloying and De‐alloying in Doped Gold Nanoparticles

Atomically precise alloying and de‐alloying processes for the formation of Ag–Au and Cu–Au nanoparticles of 25‐metal‐atom composition (referred to as Ag_xAu_25?x(SR)₁₈ and Cu_xAu_25?x(SR)₁₈, in which R=CH₂CH₂Ph) are reported. The identities of the particles were determined by matrix‐assisted laser desorption ionization mass spectroscopy (MALDI‐MS). Their structures were probed by fragmentation analysis in MALDI‐MS and comparison with the icosahedral structure of the homogold Au₂₅(SR)₁₈ nanoparticles (an icosahedral Au₁₃ core protected by a shell of Au₁₂(SR)₁₈). The Cu and Ag atoms were found to preferentially occupy the 13‐atom icosahedral sites, instead of the exterior shell. The number of Ag atoms in Ag_xAu_25?x(SR)₁₈ (x=0–8) was dependent on the molar ratio of Ag^I/Au^III precursors in the synthesis, whereas the number of Cu atoms in Cu_xAu_25?x(SR)₁₈ (x=0–4) was independent of the molar ratio of Cu^II/Au^III precursors applied. Interestingly, the Cu_xAu_25?x(SR)₁₈ nanoparticles show a spontaneous de‐alloying process over time, and the initially formed Cu_xAu_25?x(SR)₁₈ nanoparticles were converted to pure Au₂₅(SR)₁₈. This de‐alloying process was not observed in the case of alloyed Ag_xAu_25?x(SR)₁₈ nanoparticles. This contrast can be attributed to the stability difference between Cu_xAu_25?x(SR)₁₈ and Ag_xAu_25?x(SR)₁₈ nanoparticles. These alloyed nanoparticles are promising candidates for applications such as catalysis.     

Development and Properties of Surfactant‐Free Water‐Dispersible Cu2ZnSnS4 Nanocrystals: A Material for Low‐Cost Photovoltaics

A simple, yet novel hydrothermal method has been developed to synthesize surfactant‐free Cu₂ZnSnS₄ nanocrystal ink in water. The environmentally friendly, 2–4 nm ultrafine particles are stable in water for several weeks. Detailed X‐ray diffraction (XRD) and high‐resolution transmission electron microscopy revealed the formation of single‐crystalline‐kesterite‐phase Cu₂ZnSnS₄. Elemental mapping by scanning electron microscopy/energy dispersive spectrometry corroborated the presence of all four elements in a stoichiometric ratio with minor sulfur deficiency. Finally, Raman spectroscopy ruled out the possible presence of impurities of ZnS, Cu₂SnS₃, SnS, SnS₂, Cu_2?xS, or Sn₂S₃, which often interfere with the XRD and optical spectra of Cu₂ZnSnS₄. X‐ray photoelectron spectroscopic studies of the as‐synthesized samples confirmed that the oxidation states of the four elements match those of the bulk sample. Optical absorption analyses of thin film and solution samples showed high absorption efficiency (>10⁴ cm^?1) across the visible and near‐infrared spectral regions and a band gap E_g of 1.75 eV for the as‐synthesized sample. A non‐ohmic asymmetric rectifying response was observed in the I–V measurement at room temperature. The nonlinearity was more pronounced for this p‐type semiconductor when the resistance was measured against temperature in the range 180–400 K, which was detected in the hot‐point probe measurement.     

Solid-state ionics: The electrical conductivity in the Ag1−xCuxI-substituted ammonium iodide double salts

The temperature dependence of the electrical conductivity in the Ag_1?xCu_xIQI (Q = NH₄, (CH₃)₄N, and C₅H₅NCH₃) systems were measured at temperatures ranging from ?20 to 130°C under nitrogen gas flow. Temperature T_d, at which a high ionic conductivity compound decomposes to a poor conductivity compound, was determined as a function of x. Temperature T_d was raised with the increase of x in the Ag_1?xCu_xINH₄I and Ag_1?xCu_xI(CH₃)₄NI systems, but did not depend on the x value in the Ag_1?xCu_xIC₅H₅NCH₃I system; that is, the disproportionation reaction in the Ag_1?xCu_xINH₄I and (CH₃)₄NI systems was different from that in the Ag_1?xCu_xIC₅H₅NCH₃I system.     

Identification of the Chromophore in the Apatite Pigment [Sr10(PO4)6(CuxOH1−x−y)2]: Linear OCuO− Featuring a Resonance Raman Effect,an Extreme Magnetic Anisotropy,and Slow Spin Relaxation

A new chromophore has been identified in copper‐doped apatite pigments having the general composition [Sr₁₀(PO₄)₆(Cu_xOH_1?x?y)₂], in which x=0.1, 0.3 and y=0.01–0.42. By using X‐ray absorption spectroscopy, low‐temperature magnetization measurements, and synchrotron X‐ray powder structure refinement, it has been shown that the oxygenated compounds contain simultaneously diamagnetic Cu¹⁺ and paramagnetic Cu³⁺ with S=1. Cu³⁺ is located at the same crystallographic position as Cu¹⁺, being linearly coordinated by two oxygen atoms and forming the OCuO^? anion. The Raman spectroscopy study of [A₁₀(PO₄)₆(Cu_xOH_1?x?y)₂,], in which A=Ca, Sr, Ba, reveals resonance bands at 651–656 cm^?1 assigned to the symmetric stretching vibration (ν₁) of OCuO^?. The strontium apatite pigment exhibits a strong paramagnetic anisotropy with an unprecedentedly large negative zero‐field splitting parameter (D) of ≈?400 cm^?1. The extreme magnetic anisotropy causes slow magnetization relaxation with relaxation times (τ) up to 0.3 s at T=2 K, which relates the compounds to single‐ion magnets. At low temperature, τ is limited by a spin quantum‐tunneling, whereas at high temperature a thermally activated relaxation prevails with U_eff≈48 cm^?1. Strong dependence of τ on the paramagnetic center concentration at low temperature suggests that the spin‐spin relaxation dominates in the spin quantum‐tunneling process. The compound is the first example of a d‐metal‐based single‐ion magnet with S=1, the smallest spin at which an energy barrier arises for the spin flipping.     

Controllable Synthesis of Bandgap‐Tunable CuSxSe1−x Nanoplate Alloys

Composition engineering is an important approach for modulating the physical properties of alloyed semiconductors. In this work, ternary CuS_xSe_1?x nanoplates over the entire composition range of 0≤x≤1 have been controllably synthesized by means of a simple aqueous solution method at low temperature (90 °C). Reaction of Cu²⁺ cations with polysulfide/‐selenide ((S_nSe_m)^2?) anions rather than independent S_n^2? and Se_m^2? anions is responsible for the low‐temperature and rapid synthesis of CuS_xSe_1?x alloys, and leads to higher S/Se ratios in the alloys than that in reactants owing to different dissociation energies of the Se?Se and the S?S bonds. The lattice parameters ‘a’ and ‘c’ of the hexagonal CuS_xSe_1?x alloys decrease linearly, whereas the direct bandgaps increase quadratically along with the S content. Direct bandgaps of the alloys can be tuned over a wide range from 1.64 to 2.19 eV. Raman peaks of the S?Se stretching mode are observed, thus further confirming formation of the alloyed CuS_xSe_1?x phase.     

Synthesis and Structural Determination of the Disordered Bixbyite Cu3‐xSb1+xO5.5+3x/2 with Spin‐Glass Behaviour

The ternary copper antimony oxide Cu_3‐xSb_1+xO_5.5+3x/2 (x=0.23) has been synthesized under 0.8–1.3 MPa pO₂ at 1022–1082 °C. Rietveld refinements of X‐ray and neutron powder diffraction patterns concluded that the oxide adopts a bixbyite type structure, crystallising in the cubic space group Ia‐3 with the unit cell parameter a=9.61164(4) Å at room temperature from powder neutron diffraction data. The cationic 8b and 24d sites were found to be occupationally disordered where both Cu and Sb could be found on both sites. This is supported by X‐ray absorption spectroscopy experiments showing more than one possible Cu environment. There was a significant net deficiency of oxygen in the compound which was first inferred from observations of a thermochromic‐like phenomena and also seen from in situ high temperature neutron diffraction experiments. Magnetic susceptibility and magnetization measurements show paramagnetic behaviour with spin‐glass like transition below 6 K.     

Ag5Te2Cl1−xBrx (x = 0 – 0.65) and Ag5Te2−ySyCl (y = 0 – 0.3): Variation of Physical Properties in Silver(I) Chalcogenide Halides

The structures, thermal and physical properties of ion conducting polymorphic Ag₅Te₂Cl_1?xBr_x and Ag₅Te_2?ySyCl have been investigated. A maximum substitution degree of x = 0.65 and y = 0.3 was derived from X‐ray powder diffraction. Mixtures of silver halides, silver chalcogenides and Ag₃TeBr were observed for higher substitution degrees. Both silver chalcogenide halide systems show a Vegard type behaviour. Single crystal structure determinations of selected materials were performed at different temperatures to analyse the silver distribution in the tetragonal high temperature α‐ and the monoclinic room temperature β‐phases. After non‐harmonic refinement of the silver positions detailed joint probability density function analysis (jpdf) and determination of one particle potentials (opp) were carried out to investigate the diffusion pathways and bottlenecks of ion transport for those materials. A preferred anisotropic ion transport along the diffusion pathways for the α‐ and 1D zig‐zag diffusion pathways for the β‐phases were found. α–β and β‐γ phase transitions were determined by DSC and DTA methods and conductivities were measured using temperature dependent impedance spectroscopy. The substitution of tellurium by sulphur lowered the α–β phase transition from 334 K (Ag₅Te₂Cl) to 270 K (Ag₅Te_1.8S_0.2Cl) while the opposite trend was found for the Ag₅Te₂Cl_1?xBrx phases. The α–β phase transition of Ag₅Te₂Cl_0.35Br_0.65 at 343 K represents the highest transition observed for the silver chalcogenide halides under discussion. Total conductivities of approx. 1 Ω^?1 cm^?1 (α‐Ag₅Te₂Cl_0.5Br_0.5) and 0.24 Ω^?1 cm^?1 (α‐Ag₅Te_1.8S_0.2Cl) at 473 K were found being slightly higher (Br) and lower (S) than the conductivity observed for α‐Ag₅Te₂Cl. A conductivity jump of more than two orders of magnitude, related to the α–β phase transitions, within the temperature range from 270 to 343 K is adjustable by simple variation of the composition and is therefore an extraordinary feature of these materials. The total conductivity is linearly correlated to the volume of the anion substructure and can be varied within more than half an order of magnitude.     

Luminescent Metal–Organic Frameworks (MOFs) as a Chemopalette: Tuning the Thermochromic Behavior of Dual‐Emissive Phosphorescence by Adjusting the Supramolecular Microenvironments

Two classical copper(I)‐cluster‐based luminophores, namely, Cu₄I₄ and [Cu₃Pz₃]₂ (Pz=pyrazolate), are immobilized in a supramolecular system through the formation of metal–organic framework (MOF) materials. This series of luminescent MOF materials, namely, [Cu₄I₄(NH₃)Cu₃( L1 )₃]_n, [Cu₄I₄(NH₂CH₃)Cu₃( L1 )₃]_n, and [Cu₄I₄Cu₃( L2 )₃]_n ( L1 =3‐(4‐pyridyl)‐5‐(p‐tolyl)pyrazolate; L2 =3‐(4‐pyridyl)‐5‐(2,4‐dimethylphenyl)pyrazolate), exhibit diverse thermochromism attributed to the relative functioning efficacy of the two coordination luminophores. Such an intriguing chemopalette effect is regulated by the different supramolecular microenvironments between the two‐dimensional layers of these MOFs, and in particular, by the fine‐tuned Cu–Cu distances in the excimeric [Cu₃Pz₃]₂ luminophore. The structure–property elucidation of the thermochromic behavior allows one to understand these optical materials with unusual dual‐emissive properties.     

Polyaniline‐Modified Silver and Binary Silver‐Cobalt Catalysts for Oxygen Reduction Reaction

Novel dendrite‐like silver particles were electrodeposited on Ti substrates from a supporting electrolyte‐free 30 mmol L^?1 Ag(NH₃)₂⁺ solution, to synthesize the den‐Ag/Ti electrode. Binary Ag_xCo_y/Ti electrodes with different Ag:Co atomic ratios were further obtained by electrodeposition of Co particles on the den‐Ag/Ti electrode. Polyaniline (PANI) modified den‐Ag/Ti and Ag_xCo_y/Ti electrodes, PANI(n)‐den‐Ag/Ti and PANI(n)‐Ag_xCo_y/Ti, were also obtained by cyclic voltammetry at different numbers of cycles (n) in acidic and alkaline solutions containing aniline, respectively. All these electrodes exhibit high electroactivity for oxygen reduction reaction (ORR) in alkaline solution and their electroactivities follow the order: PANI(15)‐Ag₃₁Co₆₉/Ti>Ag₃₁Co₆₉/Ti>PANI(20)‐den‐Ag/Ti>den‐Ag/Ti. Among them, PANI(15)‐Ag₃₁Co₆₉/Ti displays the highest electrocatalytic activity for ORR with a much positive onset potential of 0 V (vs. Ag/AgCl) and a high ORR current density of 1.2 mA cm^?2 at ?0.12 V (vs. Ag/AgCl). The electrocatalysts are electrochemically insensitive to methanol and ethanol oxidation, and, as cathode electrocatalysts of direct alcohol fuel cells, can resist poisoning by the possible alcohol crossover from the anode.     

Tandem Silver Cluster Isomerism and Mixed Linkers to Modulate the Photoluminescence of Cluster‐Assembled Materials

Silver chalcogenolate cluster assembled materials (SCAMs) are a category of promising light‐emitting materials the luminescence of which can be modulated by variation of their building blocks (cluster nodes and organic linkers). The transformation of a singly emissive [Ag₁₂(SBu^t)₈(CF₃COO)₄(bpy)₄]_n (Ag₁₂bpy, bpy=4,4′‐bipyridine) into a dual‐emissive [(Ag₁₂(SBu^t)₆(CF₃COO)₆(bpy)₃)]_n (Ag₁₂bpy‐2) via cluster‐node isomerization, the critical importance of which was highlighted in dictating the photoluminescence properties of SCAMs. Moreover, the newly obtained Ag₁₂bpy‐2 served to construct visual thermochromic Ag₁₂bpy‐2/NH₂ by a mixed‐linker synthesis, together with dichromatic core–shell Ag₁₂bpy‐2@Ag₁₂bpy‐NH₂‐2 via solvent‐assisted linker exchange. This work provides insight into the significance of metal arrangement on physical properties of nanoclusters.     

Synthese,Kristallstruktur und festkörper‐NMR‐spektroskopische Untersuchung neuer Oxonitridosilicate der Mischkristallreihe Ba4−xCaxSi6N10O

The new oxonitridosilicates Ba_4?xCa_xSi₆N₁₀O have been synthesized by means of high‐temperature synthesis in a radio‐frequency furnace, starting from calcium, barium, silicon diimide and amorphous silicon dioxide. The maximum reaction temperature was at about 1450 °C. The solid solution series Ba_4?xCa_xSi₆N₁₀O with a phase width 1.81 ≤ x ≤ 2.95 was obtained. The crystal structure of Ba_1.8Ca_2.2Si₆N₁₀O was determined by X‐ray single‐crystal structure determination (P2₁3, no. 198), a = 1040.2(1) pm, Z = 4, wR2 = 0.082). It can be described as a highly condensed network of corner‐sharing SiN₄ and SiON₃ tetrahedra, the voids of which are occupied by the alkaline earth ions. The structure is isotypic with that of BaEu(Ba_0.5Eu_0.5)YbSi₆N₁₁. In the ²⁹Si solid‐state MAS‐NMR spectrum two isotropic resonances at ?50.0 and ?53.6 ppm were observed.     

Copper‐Based Ternary and Quaternary Semiconductor Nanoplates: Templated Synthesis,Characterization, and Photoelectrochemical Properties

Two‐dimensional (2D) copper‐based ternary and quaternary semiconductors are promising building blocks for the construction of efficient solution‐processed photovoltaic devices at low cost. However, the facile synthesis of such 2D nanoplates with well‐defined shape and uniform size remains a challenge. Reported herein is a universal template‐mediated method for preparing copper‐based ternary and quaternary chalcogenide nanoplates, that is, CuInS₂, CuIn_xGa_1?xS₂, and Cu₂ZnSnS₄, by using a pre‐synthesized CuS nanoplate as the starting template. The various synthesized nanoplates are monophasic with uniform thickness and lateral size. As a proof of concept, the Cu₂ZnSnS₄ nanoplates were immobilized on a Mo/glass substrate and used as semiconductor photoelectrode, thus showing stable photoelectrochemical response. The method is general and provides future opportunities for fabrication of cost‐effective photovoltaic devices based on 2D semiconductors.     

Post‐Synthetic Monovalent Central‐Metal Exchange,Specific I2 Sensing,and Polymerization of a Catalytic [3×3] Grid of [CuII5CuI4L6]⋅(I)2⋅13 H2O

From a predesigned grid, [Cu^II₅Cu^I₄L₆] ? (I)₂ ? 13 H₂O ( 1 ), in which LH₂ was a pyrazinyl‐triazolyl‐2,6‐substituted pyridine, we successfully synthesized an extended 3D complex, ¹_∞[{Cu^II₅Cu^I₈L₆}{μ‐[Cu^I₃(CN)₆]}₂ ? 2 CH₃‐ CN] ( 2 ), that displayed unprecedented coexistence of all the five known coordination geometries of copper. Grid 1 displayed monovalent central metal exchange (CME) of Cu^I for Ag^I for the first time, as well as the formation of tri‐iodide in the crystalline state. These systems were investigated for their magnetic properties. Remarkably, grid 1 showed much higher catalytic activity than the Ag‐exchanged product for synthesis of a substituted triazole, 1‐benzyl‐4‐phenyl‐1H‐1,2,3‐triazole.     

Combined Experimental and Computational Studies of a Na2Ni1−xCuxFe(CN)6 Cathode with Tunable Potential for Aqueous Rechargeable Sodium‐Ion Batteries

Herein, potential‐tunable Na₂Ni_1?xCu_xFe(CN)₆ nanoparticles with three‐dimensional frameworks and large interstitial spaces were synthesized as alternative cathode materials for aqueous sodium‐ion batteries by controlling the molar ratio of Ni^II to Cu^II at ambient temperature. The influence of the value of x on the crystalline structure, lattice parameters, electrochemical properties, and charge transfer of the resultant compound was explored by using powder X‐ray diffractometry, density functional theory, cyclic voltammetry, galvanostatic charge–discharge techniques, and Bader charge analysis. Of the various formulations investigated, that with x=0.25 delivered the highest reversible capacity, superior rate capability, and outstanding cycling performance. These attributes are ascribed to its unique face‐centered cubic structure for facile sodium‐ion insertion/extraction and the strong interactions between Cu and N atoms, which promote structural stability.     

Composition-induced phase transition in a [Ag<Subscript>2</Subscript>HgI<Subscript>4</Subscript>:0.2AgI] mixed composite system doped with CuI

A novel composite superionic system, [Ag₂HgI₄:0.2AgI]:xCuI, (x = 0.2, 0.4, 0.6 mol. wt.%), was prepared and [Ag₂HgI₄:0.2AgI] mixed system was used as the host. Electrical conductivity was measured to study the transition behavior at frequencies of 100 Hz, 120 Hz, 1 kHz, and 10 kHz in the temperature range 90°–170°C by a Gen Rad 1659 RLC Digibridge. Sharp increase in conductivity was observed for β-α phase transitions. As a result of increase in the dopant-to-host ratio, the conductivity of the system exhibited Arrhenius (thermally activated)-type behavior. X-ray powder diffraction, differential scanning calorimetry (DSC), differential thermal analysis (DTA) and thermo-gravimetric analysis (TGA) studies confirmed the doping effect on the transition in the host, the phase transition temperature increased with an increase in the dopant concentration. Activation energies for the system in eV both for the pretransition and post-transition phase transformations are reported. The addition of CuI to [Ag₂HgI₄:0.2AgI] shifted the phase transition of the host [Ag₂HgI₄:0.2AgI], due to an interaction between [Ag₂HgI₄:0.2AgI] and CuI.     

Cu Doping-Induced Transformation from [Ag62S12(SBut)32]2+ to [Ag62−xCuxS12(SBut)32]4+ Nanocluster

The change in the valence state of nanocluster can induce remarkable changes in the properties and structure. However, achieving the valence state changes in nanoclusters is still a challenge. In this work, we use Cu²⁺ as dopant to “oxidize” [Ag₆₂S₁₂(SBu^t)₃₂]²⁺ (4 free electrons) to obtain the new nanocluster: [Ag_62−xCu_xS₁₂(SBu^t)₃₂]⁴⁺ with 2 free electrons. As revealed by its structure, the [Ag_62−xCu_xS₁₂(SBu^t)₃₂]⁴⁺ (x=10∼21) has a similar structure to that of [Ag₆₂S₁₂(SBu^t)₃₂]²⁺ precursor and all the Cu atoms occupy the surface site of nanocluster. It′s worth noting that with the Cu atoms doping, the [Ag_62−xCu_xS₁₂(SBu^t)₃₂]⁴⁺ nanocluster is more stable than [Ag₆₂S₁₂(SBu^t)₃₂]²⁺ at higher temperature and in electrochemical cycle. This result has laid a foundation for the subsequent application and exploration. Overall, this work reveals crystals structure of a new Ag−Cu nanocluster and offers a new insight into the electron reduction/oxidation of nanocluster.