Tip Shaping for ZnO Nanorods via Hydrothermal Growth of ZnO Nanostructures in a Stirred Aqueous Solution

To enhance the field emission (FE) properties of emitters based on ZnO nanostructures, the growth of ZnO nanostructures on ZnO nanorods (NRs) (1–1.2 μm in length and ∼200 nm in diameter) in a disturbed hydrothermal growth (HTG) solution is demonstrated. Experimental results reveal that the degree of disturbance of the aqueous solution determines both the shape and location of the synthesized ZnO nanostructures. For stirring speeds of 300 and 600 rpm (rpm), NR-like ZnO nanostructures with a reduced uniform diameter (70–120 nm) and a tapered shape but a rough surface are grown on the basal plane of ZnO NRs, respectively. For stirring speeds of 900 and 1150 rpm, ZnO needles (40–70 nm and 15–20 nm in diameter, respectively) were synthesized along the {101̅0} planes of the ZnO NRs with coherent c-planes. FE characteristics of ZnO-NRs emitters with and without the second stage growth of ZnO nanostructures are reported and compared. Possible growth mechanisms which govern the physical characteristics of the ZnO nanostructures synthesized in the HTG process are proposed and discussed

[Ag₇(H){E₂P(OR)₂}₆] (E = Se, S): Precursors for the Fabrication of Silver Nanoparticles

Reactions of Ag­(I) salt, NH₄(E₂P­(OR)₂) (R = ⁱPr, Et; E = Se, S), and NaBH₄ in a 7:6:1 ratio in CH₂Cl₂ at room temperature, led to the formation of hydride-centered heptanuclear silver clusters, [Ag₇(H)­{E₂P­(OR)₂}₆] (R = ⁱPr, E = Se (<b>3</b>): R = Et; E = S­(<b>4</b>). The reaction of [Ag₁₀(E)­{E₂P­(OR)₂}₈] with NaBH₄ in CH₂Cl₂ produced [Ag₈(H)­{E₂P­(OR)₂}₆]­(PF₆) (R = ⁱPr, E = Se (<b>1</b>): R = Et; E = S­(<b>2</b>)), which can be converted to clusters <b>3</b> and <b>4</b>, respectively, via the addition of 1 equiv of borohydride. Intriguingly clusters <b>1</b> and <b>2</b> can be regenerated via adding 1 equiv of Ag­(CH₃CN)₄PF₆ to the solution of compounds <b>3</b> and <b>4</b>, respectively. All complexes have been fully characterized by NMR (¹H, ⁷⁷Se, ¹⁰⁹Ag) spectroscopy, UV–vis, electrospray ionization mass spectrometry (ESI-MS), FT-IR, thermogravimetric analysis (TGA), and elemental analysis, and molecular structures of <b>3</b>_<b>H</b> and <b>4</b>_<b>H</b> were clearly established by single crystal X-ray diffraction. Both <b>3</b>_<b>H</b> and <b>4</b>_<b>H</b> exhibit a tricapped tetrahedral Ag₇ skeleton, which is inscribed within an E₁₂ icosahedron constituted by six dialkyl dichalcogenophosphate ligands in a tetrametallic-tetraconnective (μ₂, μ₂) bonding mode. Density functional theory (DFT) calculations on the models [Ag₇(H)­(E₂PH₂)₆] (E = Se: <b>3′</b>; E = S: <b>4′</b>) yielded to a tricapped, slightly elongated tetrahedral silver skeleton, and time-dependent DFT (TDDFT) calculations reproduce satisfyingly the UV–vis spectrum with computed transitions at 452 and 423 nm for <b>3′</b> and 378 nm for <b>4′</b>. Intriguingly further reactions of [Ag₇(H)­{E₂P­(OR)₂}₆] with 8-fold excess amounts of NaBH₄ produced monodisperse silver nanoparticles with an averaged particle size of 30 nm, which are characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD), and UV–vis absorption spectrum

Ferrocene-Functionalized Cu(I)/Ag(I) Dithiocarbamate Clusters

A series of compounds, namely, [Cu₈(μ₄-H)­{S₂CN­MeCH₂Fc}₆]­(PF₆) (<b>1</b>), [Cu₇(μ₄-H) {S₂CN^<i>i</i>PrCH₂Fc}₆] (<b>2</b>), [Cu₃{S₂CN­(Bz) (CH₂Fc)}₂(dppf)₂]­(PF₆) (<b>3</b>), and [Ag₂{S₂CNMe­(CH₂Fc)}₂(PPh₃)₂] (<b>4</b>) (dppf = 1,1′-bis­(diphenylphosphino)­ferrocene), supported by multiferrocene assemblies, were synthesized. All the compounds were characterized by ¹H NMR, Fourier transform infrared, elemental analysis, and electrospray ionization mass spectrometry techniques. Single-crystal X-ray structural analysis revealed that <b>1</b> is a monocationic octanuclear Cu^I cluster and that <b>2</b> is a neutral heptanuclear Cu^I cluster with tetracapped tetrahedral (<b>1</b>) and tricapped tetrahedral (<b>2</b>) geometries entrapped with an interstitial hydride, anchored by six ferrocene units at the periphery of the core. Compounds <b>3</b> and <b>4</b> comprise trimetallic Cu^I and dimetallic Ag^I cores enfolded by four and two ferrocene moieties. Interestingly both chelating and bridging modes of binding are observed for dppf ligand in <b>3</b>. Further the formation and isolation of polyhydrido copper clusters [Cu₂₈H₁₅{S₂CN^<i>i</i>PrCH₂Fc}₁₂]­(PF₆) (<b>5</b>) and [Cu₂₈H₁₅{S₂CN^<i>n</i>Bu₂}₁₂]­(PF₆) (<b>7</b>), stabilized by bulky ferrocenyl and <i>n</i>-butyl dithiocarbamate ligands, was demonstrated. They are readily identified by ²H NMR studies on their deuterium analogues, [Cu₂₈D₁₅{S₂CN^<i>i</i>PrCH₂Fc}₁₂]­(PF₆) (<b>6</b>) and [Cu₂₈D₁₅{S₂CN^<i>n</i>Bu₂}₁₂]­(PF₆) (<b>8</b>). Though the structure details as well as spectroscopic characterizations of <b>5</b> are yet to be investigated, the compound <b>7</b> is fully characterized by variety of spectroscopy including single-crystal X-ray diffraction. The cyclic voltammetry studies for compounds <b>1</b>, <b>2</b>, and <b>4</b> display irreversible redox peaks for Fe²⁺/Fe³⁺ couple wherein the reduction peaks are not well-resolved due to some adsorption of the complex onto the electrode surface

Anion Encapsulation and Geometric Changes in Hepta- and Hexanuclear Copper(I) Dichalcogeno Clusters: A Theoretical and Experimental Investigation

Whereas stable octanuclear clusters of the type M^I₈(E^∩E)₆ (M = Cu, Ag; E^∩E = dithio or diseleno ligand) are known for being able to encapsulate a hydride or main-group anion under some circumstances, only the related hydride-containing heptanuclear [M^I]₇(H)­(E^∩E)₆ and empty hexanuclear [M^I]₆(E^∩E)₆ species have been characterized so far. In this paper we investigate by the means of theoretical calculations and experiments the viability of empty and anion-centered clusters of the type [Cu^I]₇(X)­(E^∩E)₆ and [Cu^I]₆(X)­(E^∩E)₆ (X = vacancy, H or a main-group atom). The theoretical prediction for the existence of anion-containing heptanuclear species, the shape of which is modulated by the anion nature and size, have been fully confirmed by the synthesis and characterization of [Cu₇(X)­{S₂P­(OⁱPr)₂}₆] (X = H, Br). This consistency between experiment and theory allows us to predict the stability and shape-modulated structure of a whole series of [Cu^I]₇(X)­(E^∩E)₆ (X = vacancy, H, O, S, halogen) and [Cu^I]₆(X)­(E^∩E)₆ (X = H, halogen) clusters

Anion Encapsulation and Geometric Changes in Hepta- and Hexanuclear Copper(I) Dichalcogeno Clusters: A Theoretical and Experimental Investigation

Whereas stable octanuclear clusters of the type M^I₈(E^∩E)₆ (M = Cu, Ag; E^∩E = dithio or diseleno ligand) are known for being able to encapsulate a hydride or main-group anion under some circumstances, only the related hydride-containing heptanuclear [M^I]₇(H)­(E^∩E)₆ and empty hexanuclear [M^I]₆(E^∩E)₆ species have been characterized so far. In this paper we investigate by the means of theoretical calculations and experiments the viability of empty and anion-centered clusters of the type [Cu^I]₇(X)­(E^∩E)₆ and [Cu^I]₆(X)­(E^∩E)₆ (X = vacancy, H or a main-group atom). The theoretical prediction for the existence of anion-containing heptanuclear species, the shape of which is modulated by the anion nature and size, have been fully confirmed by the synthesis and characterization of [Cu₇(X)­{S₂P­(OⁱPr)₂}₆] (X = H, Br). This consistency between experiment and theory allows us to predict the stability and shape-modulated structure of a whole series of [Cu^I]₇(X)­(E^∩E)₆ (X = vacancy, H, O, S, halogen) and [Cu^I]₆(X)­(E^∩E)₆ (X = H, halogen) clusters

A Nanospheric Polyhydrido Copper Cluster of Elongated Triangular Orthobicupola Array: Liberation of H₂ from Solar Energy

An unprecedented air-stable, nanospheric polyhydrido copper cluster, [Cu₂₀H₁₁(S₂P­(OⁱPr)₂)₉] (<b>1</b>_<b>H</b>), which is the first example of an elongated triangular orthobicupola array of Cu atoms having <i>C</i>_3<i>h</i> symmetry, was synthesized and characterized. Its composition was primarily determined by electrospray ionization mass spectrometry, and it was fully characterized by ¹H, ²H, and ³¹P NMR spectroscopy and single-crystal X-ray diffraction (XRD). The structure of complex <b>1</b>_<b>H</b> can be expressed in terms of a trigonal-bipyramidal [Cu₂H₅]^3– unit anchored within an elongated triangular orthobicupola containing 18 Cu atoms, which is further stabilized by 18 S atoms from nine dithiophosphate ligands and six capping hydrides. The positions of the 11 hydrides revealed by low temperature XRD were supported by a density functional theory investigation on the simplified model [Cu₂₀H₁₁(S₂PH₂)₉] with <i>C</i>_3<i>h</i> symmetry. <b>1</b>_<b>H</b> is capable of releasing H₂ gas upon irradiation with sunlight, under mild thermal conditions (65 °C), or in the presence of acids at room temperature

A Nanospheric Polyhydrido Copper Cluster of Elongated Triangular Orthobicupola Array: Liberation of H₂ from Solar Energy

An unprecedented air-stable, nanospheric polyhydrido copper cluster, [Cu₂₀H₁₁(S₂P­(OⁱPr)₂)₉] (<b>1</b>_<b>H</b>), which is the first example of an elongated triangular orthobicupola array of Cu atoms having <i>C</i>_3<i>h</i> symmetry, was synthesized and characterized. Its composition was primarily determined by electrospray ionization mass spectrometry, and it was fully characterized by ¹H, ²H, and ³¹P NMR spectroscopy and single-crystal X-ray diffraction (XRD). The structure of complex <b>1</b>_<b>H</b> can be expressed in terms of a trigonal-bipyramidal [Cu₂H₅]^3– unit anchored within an elongated triangular orthobicupola containing 18 Cu atoms, which is further stabilized by 18 S atoms from nine dithiophosphate ligands and six capping hydrides. The positions of the 11 hydrides revealed by low temperature XRD were supported by a density functional theory investigation on the simplified model [Cu₂₀H₁₁(S₂PH₂)₉] with <i>C</i>_3<i>h</i> symmetry. <b>1</b>_<b>H</b> is capable of releasing H₂ gas upon irradiation with sunlight, under mild thermal conditions (65 °C), or in the presence of acids at room temperature

Shape Modulation of Octanuclear Cu(I) or Ag(I) Dichalcogeno Template Clusters with Respect to the Nature of their Encapsulated Anions: A Combined Theoretical and Experimental Investigation

M₈L₆ clusters (M = Cu­(I), Ag­(I); L = dichalcogeno ligand) are known for their ability to encapsulate various kinds of saturated atomic anions. Calculations on the models [M₈(E₂PH₂)₆]²⁺ (M = Cu­(I), Ag­(I); E = S, Se) and the ionic or neutral [M₈(X)­(E₂PH₂)₆]^<i>q</i> (X = H, F, Cl, Br, O, S, Se, N, P, C) indicate that the cubic M₈L₆ cage adapts its shape for maximizing the host–guest bonding interaction. The interplay between size, covalent and ionic bonding favors either a cubic, tetracapped tetrahedral, or bicapped octahedral structure of the metal framework. Whereas the large third- and fourth-row main group anions maintain the cubic shape, a distortion toward a tetracapped tetrahedral arrangement of the metals occurs in the case of hydride, fluoride, and oxide. The distortion is strong in the case of hydride, weak in the case of fluoride, and intermediate in the case of oxide. Density functional theory (DFT) calculations predict a bicapped octahedral architecture in the case of nitride and carbide. These computational results are supported by X-ray structures, including those of new fluorine- and oxygen-containing compounds. It is suggested that other oxygen-containing as well as so far unknown nitride-containing clusters should be feasible. For the first time, the dynamical behavior of the encapsulated hydride has been investigated by metadynamics simulations. Our results clearly demonstrate that the interconversion mechanism between two identical tetracapped tetrahedral configurations occurs through a succession of M-H bonds breaking and forming which present very low activation energies and which involve a rather large number of intermediate structures. This mechanism is full in accordance with ¹⁰⁹Ag and ¹H state NMR measurements