Adsorbate-Induced Phase Transformation of Ambient Stable Noncubic Lattices in Au Microcrystallites

Metals possess crystal structure-dependent properties, be it in the bulk, micro-, or in nanostructures. The stability of Au microcrystallites stabilized in unconventional body-centered orthorhombic and tetragonal [termed as bc­(o,t)] lattices, under common chemical adsorbates, hexadecanethiol (HDT) and Na2S, is explored in this study. Treatment with HDT selectively enhances the (101)bc(o,t) diffraction intensity while with Na2S results in an irreversible bc­(o,t) to fcc lattice transformation, which is remarkable, given the extraordinary stability of these lattices, even under high pressures and temperatures. These observations were further supported by selected area electron diffraction measurements. Importantly, the overall crystallite morphology remained similar as examined using high-resolution scanning electron microscopy. The calculated adsorption energies using density functional theory for S adsorption on various crystallite facets reveal higher stability for fcc over the metastable bc­(o,t) lattices, and the trend is opposite for the adsorption of thiol. With the latter, the (101)bc(o,t) facets are favored over (002)bc(o,t), which reflects in the selective enhancement of the diffraction intensity and indeed in the overall crystallinity itself. The aspect related to facet reorientation induced by adsorbates relates to similar changes observed in polycrystalline fcc Au itself under similar conditions

Enhanced Air Stability in REPb₃ (RE = Rare Earths) by Dimensional Reduction Mediated Valence Transition

We conceptually selected the compounds REPb3 (RE = Eu, Yb), which are unstable in air, and converted them to the stable materials in ambient conditions by the chemical processes of “nanoparticle formation” and “dimensional reduction”. The nanoparticles and the bulk counterparts were synthesized by the solvothermal and high-frequency induction furnace heating methods, respectively. The reduction of the particle size led to the valence transition of the rare earth atom, which was monitored through magnetic susceptibility and X-ray absorption near edge spectroscopy (XANES) measurements. The stability was checked by X-ray diffraction and thermogravimetric analysis over a period of seven months in oxygen and argon atmospheres and confirmed by XANES. The nanoparticles showed outstanding stability toward aerial oxidation over a period of seven months compared to the bulk counterpart, as the latter one is more prone to the oxidation within a few days

A Ligand-Bridged Heterotetranuclear (Fe₂Cu₂) Redox System with Fc/Fc⁺ and Radical Ion Intermediates

The redox pair [(μ-abcp)­{Cu­(dppf)}₂]^2+/+ (abcp = 2,2′-azobis­(5-chloropyrimidine) and dppf =1,1′-bis­(diphenylphosphino)­ferrocene) has been structurally characterized to reveal the lengthening of the NN and shortening of the CN_azo bonds on reduction, each by about 0.04 Å. These and other charge forms, [(μ-abcp)­{Cu­(dppf)}₂]^<i>n</i>+ (n = 0, 3+, 4+), have been investigated spectroelectrochemically (UV–vis–near-IR, EPR) to reveal an abcp-based second reduction and a stepwise ferrocene-centered oxidation of the 2+ precursor. In contrast to the small but detectable comproportionation constant of <i>K</i>_c = 17 for the Fc/Fc⁺ mixed-valence (3+) charge state, the monocationic radical complex exhibits a very large <i>K</i>_c value of 10¹⁶

Red-Emitting Copper Nanoclusters: From Bulk-Scale Synthesis to Catalytic Reduction

A large-scale, easy synthesis of red fluorescent copper nanoclusters (CuNCs) from a cheap source copper acetate, monohydrate has been reported. A proteinaceous amino acid cysteine has been used to stabilize these clusters at room temperature. These nanoclusters have been thoroughly characterized by UV–vis absorption, fluorescence spectroscopy, matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) spectrometry, transmission electron microscopy (TEM), X-ray powder diffraction analysis, cyclic voltametry (CV), and X-ray photoelectron spectroscopy. MALDI-TOF analysis indicates that the nanocluster is a Cu5(Cys)3 species. Computational studies revealed the energy optimized structure of Cu5(Cys)3 with most possible arrangements of Cu atoms and their interactions with stabilizing ligands. It is evident from the structure that vacant Cu sites are available; hence, these sites can be used for binding with substrate molecules for catalytic reactions. Interestingly, these as-synthesized red-emitting nanocluster catalyze the degradation of 4-nitrophenol (toxic chemical used in industries) to almost nontoxic 4-aminophenol at room temperature. These nanoclusters (powdered) can also be recycled as catalyst for another time. This type of new nanocatalyst for the organic transformation of a toxic to nontoxic material holds future promise for the development of novel large-scale nanocatalytic materials

A Ligand-Bridged Heterotetranuclear (Fe₂Cu₂) Redox System with Fc/Fc⁺ and Radical Ion Intermediates

The redox pair [(μ-abcp)­{Cu­(dppf)}₂]^2+/+ (abcp = 2,2′-azobis­(5-chloropyrimidine) and dppf =1,1′-bis­(diphenylphosphino)­ferrocene) has been structurally characterized to reveal the lengthening of the NN and shortening of the CN_azo bonds on reduction, each by about 0.04 Å. These and other charge forms, [(μ-abcp)­{Cu­(dppf)}₂]^<i>n</i>+ (n = 0, 3+, 4+), have been investigated spectroelectrochemically (UV–vis–near-IR, EPR) to reveal an abcp-based second reduction and a stepwise ferrocene-centered oxidation of the 2+ precursor. In contrast to the small but detectable comproportionation constant of <i>K</i>_c = 17 for the Fc/Fc⁺ mixed-valence (3+) charge state, the monocationic radical complex exhibits a very large <i>K</i>_c value of 10¹⁶

Electrochemical Evidence for Hemilabile Coordination of 1,3-Dimethyllumazine to [1,1′-Bis(diorganophosphino)ferrocene]copper(I)

The complex cations [Cu­(dippf)­(DML)]+ ([1]+) and [Cu­(dppf)­(DML)]+ ([2]+), where dippf = 1,1′-bis­(diisopropylphosphino)­ferrocene, dppf = 1,1′-bis­(diphenylphosphino)­ferrocene, and DML = 1,3-dimethyllumazine, were prepared and crystallized as BF4– or PF6– salts. Structure determinations of the tetrafluoroborates revealed asymmetric O4,N5 chelation of DML to copper­(I) with longer Cu–O bonds of about 2.25 Å. Reversible oxidation to [1]2+ and [2]2+ proceeds at the ferrocene units, while reduction leads to the neutral radical complexes [1] and [2] with the unpaired electron localized on the DML ligand. The occurrence of two voltammetric steps for the one-electron-reduction process is attributed to a two-species equilibrium caused by the hemilabile coordination of DML. Electrochemical and spectroelectrochemical measurements (UV–vis, IR) reveal increased coordination lability of the reduced complexes and their slow fragmentation

Copper Nanoclusters for Catalytic Carbon–Carbon and Carbon–Nitrogen Bond Formations

Newly synthesized blue-emitting few-atom copper nanoclusters (CuNCs) have been successfully utilized for catalyzing C­(sp2)–C­(sp2) and C­(sp2)–N­(sp3) bond formations. Various substituted biphenyls and 2° aromatic amines have been synthesized in good yield using this copper catalyst at facile reaction conditions in dimethyl sulfoxide. The amount of required nanocatalysts is as low as merely 2 mol % for carrying out these reactions. These types of copper nanoclusters are promising as potential and cheap catalysts for replacing conventional metal nanoparticles and heavy-metal-ion-based organic catalysts. The optimized structure of Cu6(GS)2 [GS = C10H16N3O6S] from computational studies revealed the perfect arrangements of Cu atoms in CuNCs and their interactions with stabilizing ligands. It is evident from the structure that some free Cu sites are available in the nanocluster species. These kinds of coordinatively unsaturated sites are highly active toward the catalytic reactions. Matrix-assisted laser desorption ionization–time-of-flight (MALDI–TOF) analysis also supports the computational hypothesis. Interestingly, matrix-assisted laser desorption ionization–time-of-flight mass spectrometry (MALDI–TOF MS) and computational studies revealed the formation of several reaction key intermediates in catalyzing C­(sp2)–C­(sp2) bond formation

Epitaxial Orientation Angle Tuned Disk-on-Rod Nanoheterostructures for Boosting Charge Transfer

Controlling the compositions of Se­(VI) and Te­(VI) ions in a 2D disk on 1D structures of Sb­(V) chalcogenides, disk-on-rod heterostructures having three different epitaxial angles with different surface facets are reported. Te injection temperature determined the composition, ensuring heterostructure formation with trigonal Sb2SexTe3–x disks on orthorhombic Sb2Se3 rods having orientation angles 180°, 135°, and 90°. The growth kinetics of disks connected at one/two heads of parent rods is manipulated using an Se precursor as a limiting reagent. Theoretical calculations established the energy minimization of different orientations, their possible formation, and suitability in energy transfer applications. Electrochemical measurements were also in agreement with theoretical calculations. Hence, this is a case study of advanced modular synthesis of disk-on-rod nanostructures, leading a step further in nanocrystal engineering for more desirable complex structures and their charge transfer property

Electrochemical Evidence for Hemilabile Coordination of 1,3-Dimethyllumazine to [1,1′-Bis(diorganophosphino)ferrocene]copper(I)

The complex cations [Cu­(dippf)­(DML)]⁺ ([<b>1</b>]⁺) and [Cu­(dppf)­(DML)]⁺ ([<b>2</b>]⁺), where dippf = 1,1′-bis­(diisopropylphosphino)­ferrocene, dppf = 1,1′-bis­(diphenylphosphino)­ferrocene, and DML = 1,3-dimethyllumazine, were prepared and crystallized as BF₄^– or PF₆^– salts. Structure determinations of the tetrafluoroborates revealed asymmetric O⁴,N⁵ chelation of DML to copper­(I) with longer Cu–O bonds of about 2.25 Å. Reversible oxidation to [<b>1</b>]²⁺ and [<b>2</b>]²⁺ proceeds at the ferrocene units, while reduction leads to the neutral radical complexes [<b>1</b>] and [<b>2</b>] with the unpaired electron localized on the DML ligand. The occurrence of two voltammetric steps for the one-electron-reduction process is attributed to a two-species equilibrium caused by the hemilabile coordination of DML. Electrochemical and spectroelectrochemical measurements (UV–vis, IR) reveal increased coordination lability of the reduced complexes and their slow fragmentation

Eu₃Ir₂In₁₅: A Mixed-Valent and Vacancy-Filled Variant of the Sc₅Co₄Si₁₀ Structure Type with Anomalous Magnetic Properties

A new compound, Eu₃Ir₂In₁₅, has been synthesized using indium as an active metal flux. The compound crystallizes in the tetragonal <i>P</i>4/<i>mbm</i> space group with lattice parameters <i>a</i> = 14.8580(4) Å, <i>b</i> = 14.8580(4) Å, and <i>c</i> = 4.3901(2) Å. It was further characterized by SEM-EDX studies. The effective magnetic moment (μ_eff) of this compound is 7.35 μ_B/Eu ion with a paramagnetic Curie temperature (θ_p) of −28 K, suggesting antiferromagnetic interaction. The mixed-valent nature of Eu observed in magnetic measurements was confirmed by XANES measurements. The compound undergoes demagnetization at a low magnetic field (10 Oe), which is quite unusual for Eu-based intermetallic compounds. Temperature-dependent resistivity studies reveal that the compound is metallic in nature. A comparative study was made between Eu₃Ir₂In₁₅ and hypothetical vacancy-variant Eu₅Ir₄In₁₀, which also crystallizes in the same crystal structure. However, our computational studies along with control experiments suggest that the latter is thermodynamically less feasible compared to the former, and hence we propose that it is highly unlikely that an RE₅T₄X₁₀ would exist with X as a group 13 element