Metal Complex Precursors Research Articles

Preparation and Electrochemical Properties of a Gallium-Doped Zinc Oxide Electrode Decorated with Densely Gathered Palladium Nanoparticles

A novel method for chemically preparing densely gathered palladium nanoparticles (PdNPs) on a gallium-doped zinc oxide (GZO) electrode is reported. We found that PdCl42– could be captured directly on a bare GZO electrode surface simply by immersing a piece of GZO in an aqueous solution of K2PdCl4, resulting in a GZO electrode color change from transparent to yellow. The subsequent reduction of the composite electrode in an aqueous solution of NaBH4 produced a further color change to blackish-violet even after the PdCl42–-captured GZO had been washed and dried. X-ray photoelectron spectroscopy analysis confirmed the presence of Pd as PdCl42– and Pd0 on the GZO before and after reduction with NaBH4, respectively. The surface images collected using field emission scanning electronic microscopy revealed that the PdNPs were densely gathered and connected to one another. Although bare GZO electrodes have not been used extensively in voltammetric analysis, the present modification using densely gathered PdNPs shows promise as a new approach to constructing Pd-functionalized electrodes as confirmed by measuring voltammetric responses. The simple capture of metal complex precursors and nanostructuring followed by a simple reduction reaction on GZO is promising as a new and efficient fabrication method that conserves precious starting materials.

Chemical Fluid Deposition of Hf-Zr-O-based Thin Films using Supercritical Carbon Dioxide Fluid

ABSTRACTWe propose some chemical processing procedures for fabricating thin films in Hf-Zr-O system by a unique film deposition technique using supercritical carbon dioxide fluid (scCO2), i.e., supercritical fluid deposition (SCFD), which would be an prospective approach for fabricating metal-oxide films for integrated circuits because of its unique characteristics; e.g., extraction ability, transportation capability, and reaction equilibrium etc., are quite favorable for the film deposition from metal-complex precursors.The SCFD was accomplished in a closed batch-type reaction apparatus, consisting of two steps; (a) material deposition and (b) subsequent post-treatment under scCO2 atmosphere. Thin films of amorphous Hf-Zr-O were deposited on platinized silicon [(111)Pt/TiO2/(100)Si] substrates by SCFD using metal-complex precursors M[OCH(CH3)]2(C9H11O2)2 (M = Hf or Zr) at reaction temperature of 100 – 300 °C, significantly lower than those for MOCVD. These films possessed dielectric permittivity’s of approximately 20 – 25, comparable to those from conventional processes, although they still included residue of organic species that prompt the dielectric degradation under lower-frequency bias application.

Design of crystal structures, morphologies and functionalities of titanium oxide using water-soluble complexes and molecular control agents

Nature produces materials with excellent physical and chemical properties using water as a medium under ambient temperature and pressure. The current need for more highly functional and compact materials makes the mimicking of natural processes to produce these materials a very interesting approach, not only to obtain highly functionalized materials but also to reduce the environmental impact. Our research group is engaged in the development of new stable water-soluble compounds that follow natural processes for the synthesis of materials using water as a medium. This paper summarizes a hydrothermal synthesis of rutile-type titanium oxide using water-soluble titanium complexes, controlling the crystal morphology by utilizing organic molecules as shape-control agents as well as their speculative formation mechanism and superior dielectric properties of unusually shaped titanium oxide crystals. By recapitulating our results, we indicate that control of the nano- and macro-structures and functional improvement are accomplished through the development of new precursor compounds. Titanium dioxide (TiO2) with highly controlled nano (polymorph) and macro (morphology) structures was synthesized from water by hydrothermal method using a series of unique water-soluble titanium complexes. Thanks to their high stability in water, a variety of organic molecules, which act as a shape-controlling agent, can coexist, resulting in the formation of anistropically grown rutile-type TiO2. The obtained rutile crystals exhibited greatly improved functions with respect to their dielectric or photocatalytic performance. The results suggest that the chemical design of metal-complex precursors leads to achievement of high functionalization of materials.

Rh(I) Complexes Bearing N,N and N,P Ligands Anchored on Glassy Carbon Electrodes: Toward Recyclable Hydroamination Catalysts

A series of N,N-donor ligands (bis(pyrazol-1-yl)methane (bpm), bis(N-methylimidazol-2-yl)methane (bim), 1-(phenylmethyl)-4-(1H-pyrazol-1-yl methyl)-1H-1,2,3-triazole (PyT)), and one N,P-donor ligand precursor (1-(3,5-dimethylpyrazol-1-yl)(2-bromoethane) (dmPyBr)) were synthesized and functionalized with aniline. Diazotization of the aniline into an aryl diazonium, using nitrous acid in aqueous conditions, was performed in situ such that the ligands could be reductively adsorbed onto glassy carbon electrode surfaces. The N,N-donor ligands (bpm, bim, PyT) were immobilized in a single step, while several steps were required to immobilize the N,P-donor ligand (dmPyP) to prevent oxidation of the phosphine group. The complexation of the anchored ligands with the metal complex precursor ([Rh(CO)2(μ-Cl)]2) led to the formation of anchored Rh(I) complexes with each of the ligands (bpm, bim, PyT, dmPyP). X-ray photoelectron spectroscopy (XPS) confirmed the formation of the anchored ligands as well as the anchored complexes. The surface coverage of functionalized electrodes was estimated by means of cyclic voltammetry, and the nature of the coverage was close to being a monolayer for each immobilized complex. The anchored Rh(I) complexes were active as catalysts for the intramolecular hydroamination of 4-pentyn-1-amine to form 2-methyl-1-pyrroline.

Density Functional Theory Predictions of the Composition of Atomic Layer Deposition-Grown Ternary Oxides

The surface reactivity of various metal precursors with different alkoxide, amide, and alkyl ligands during the atomic layer deposition (ALD) of ternary oxides was determined using simplified theoretical models. Quantum chemical estimations of the Brønsted reactivity of a metal complex precursor at a hydroxylated surface are made using a gas-phase hydrolysis model. The geometry optimized structures and energies for a large suite of 17 metal precursors (including cations of Mg, Ca, Sr, Sc, Y, La, Ti, Zr, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, and Ga) with five different anionic ligands (conjugate bases of tert-butanol, tetramethyl heptanedione, dimethyl amine, isopropyl amidine, and methane) and the corresponding hydrolyzed complexes are calculated using density functional theory (DFT) methods. The theoretically computed energies are used to determine the energetics of the model reactions. These DFT models of hydrolysis are used to successfully explain the reactivity and resulting stoichiometry in terms of metal cation ratios seen experimentally for a variety of ALD-grown ternary oxide systems.

The secondary phosphite selenide, CpFe(CO)2P(Se)(OiPr)2, as an organometalloligand in heterometallic M–Se–P–Fe(Cp)-type complexes [M = Cr(0), W(0), Pd(ii), Pt(ii), Au(i)

The neutral metalloligand [CpFe(CO)2P(Se)(O(i)Pr)2] (Cp = η(5)-C5H5), which contains the rare secondary phosphite selenide moiety, reacts with different metal complex precursors to form six new heterobimetallic complexes containing M-Se-P-Fe(Cp) bond connectivity. The complexes [M(CO)5{CpFe(CO)2P(Se)(O(i)Pr)2}] (M = Cr, 1; M = W, 2), [MCl2{CpFe(CO)2P(Se)(O(i)Pr)2}2] (M = Pd, 3; M = Pt, 4), [Au4Cl4{CpFe(CO)2P(Se)(O(i)Pr)2}2], 5, and [AuI{CpFe(CO)2P(Se)(O(i)Pr)2}], 6, are all heterometallic, neutral, dinuclear (1, 2, 6), trinuclear (3, 4), and hexanuclear (5) complexes. The complexes were all prepared from straightforward substitution reactions (1-5) or as an adduct, 6. All new complexes were characterized by (1)H, (31)P, (77)Se NMR, infrared spectroscopy, elemental analysis and single crystal X-ray diffraction.

Laser induced forward transfer of SnO2 for sensing applications using different precursors systems

This paper presents the transfer of SnO2 by laser induced forward transfer (LIFT) for gas sensor applications. Different donor substrates of SnO2 with and without triazene polymer (TP) as a dynamic release layer were prepared. Transferring these films under different conditions were evaluated by optical microscopy and functionality. Transfers of sputtered SnO2 films do not lead to satisfactory results and transfers of SnO2 nanoparticles are difficult. Transfers of SnO2 nanoparticles can only be achieved when applying a second laser pulse to the already transferred material, which improves the adhesion resulting in a complete pixel. A new approach of decomposing the transfer material during LIFT transfer was developed. Donor films based on UV absorbing metal complex precursors namely, SnCl2(acac)2 were prepared and transferred using the LIFT technique. Transfer conditions were optimized for the different systems, which were deposited onto sensor-like microstructures. The conductivity of the transferred material at temperatures of about 400 ∘C are in a range usable for SnO2 gas sensors. First sensing tests were carried out and the transferred material proved to change conductivity when exposed to ethanol, acetone, and methane.

Synthesis and Characterization of Ce<sub>1-x</sub>Zr<sub>x</sub>O<sub>2</sub> Nanopaticles

A series of crystalline Ce1-xZrxO2 nanoparticles (where x = 0, 0.25, 0.5, 0.75 and 1.0) have been prepared by (i) hydrothermal (ii) polymer based metal-complex precursor solution reactions. Hydrothermal method was performed with diethanol amine as hydrolysis catalyst. The effect of reaction conditions on the size of particles and their morphology were investigated. In the polymer based method, by calcination of suitable polymer precursor solutions at a temperature range between 300 and 450 °C along with variation in the period of time, the metal oxide powders were subsequently obtained. The prepared powders have been characterized by powder X-ray diffraction (XRD), X-ray Fluorescence (XRF) .These studies reveled that zirconium is a good host for insertion into Cerium oxide in fluorite structure. The as-prepared samples were further characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The average diameter of the nanoparticles were calculated from line broadening of XRD peaks and confirmed by SEM and TEM studies.

Conversion of biomass products to energy sources in the presence of nanocatalysts and membrane-catalyst systems

A particular role in the harmonious exploitation of raw materials is assigned to organic sources of fuels based on renewable biomass. The most promising feedstocks of major energy sources, such as hydrogen and organic components of motor fuels, include ethanol and other bioalcohols, i.e., the primary products of its conversion. In this work, we describe the results for new reactions of conversion of ethanol and a mixture of ethanol and glycerol, which are the major products of biomass, to the C3–C10 alkane-olefin fraction in the presence of nanoscale mono- and bimetal-containing active components supported on γ-Al2O3 (〈d〉 = 5–8 nm) and on the inner surface of microchannels of ceramic membranes (〈d〉 = 15–20 nm). Mono- and bimetallic alkoxide and acetate complexes are used as precursors. It is found that the selectivity for the ethanol conversion to aliphatic hydrocarbons, as well as the content of branched structures, heavily depends on the nuclearity and composition of metal-complex precursors supported on γ-Al2O3. It is found for the first time that glycerol exhibits high reactionary ability in the reaction of cross-condensation of the carbon skeleton of alcohols of different nature. In the presence of a Ta-Re-containing system, a mixture of ethanol and glycerol is converted to 60% of C4–C10+ olefins, which contain up to 50% of branched structures. It is shown that by varying the composition of Pd-Zn-containing active components, it is possible to targetedly convert ethanol to the olefin, alkane, or alkane-olefin fraction. Porous membrane-catalyst systems are designed to produce hydrogen and syngas from biomass products; the systems exhibit high activity in the carbon dioxide and steam reforming of ethanol, a mixture of ethanol and glycerol, and acetic acid. A scheme for the production of a wide range of valuable organic products based on bioalcohols containing no toxic impurities and independent of crude oil is described. According to this scheme, alkanes derived from ethanol and other bioalcohols are the major components of motor fuels; a large number of organic synthesis products can be derived from olefins, hydrogen, and carbon monoxide in the carbonylation/hydrocarbonylation processes.

Polymer catenanes via a supramolecularly templated ATRP initiator

Synthesis of polymer catenanes via a living radical polymerization and supramolecular template approach are demonstrated. The ring closure was performed via atom transfer radical cross coupling (ATRC) to obtain polymer catenanes from the linear polymer metal complex precursor.

Photoactivated Biological Activity of Transition‐Metal Complexes

AbstractPhotochemical activation is a very attractive way to achieve precise spatial and temporal control of the biological action of transition‐metal complexes that behave as inactive “prodrugs” in the dark. A significant amount of work has been devoted to metal complexes that act on DNA. In this area, focus has been on ruthenium and rhodium polypyridyl compounds, but copper, iron, cobalt, and vanadium complexes also find increasing application as photoactivable DNA cleaving agents, with excitation sometimes even possible in the near IR region. Most often, the activity of these systems is based on the formation of reactive radical species. Another promising approach is the photochemical generation of covalent DNA binders from inactive precursors, as, for example, by some platinum(IV) compounds. The photolytic liberation of biologically active small molecules from inactive metal complex precursors has also become the target of recent research efforts and complements work on purely organic “caged” compounds. The significant progress made on light‐induced liberation of neurotransmitters as well as small molecule messengers like nitric oxide (NO) or carbon monoxide (CO) is also summarized here.

A Novel Approach for Monodisperse Samarium Orthovanadate Nanocrystals: Controlled Synthesis and Characterization

A new solvothermal approach has been developed for the synthesis of monodisperse and well-crystallized SmVO4 nanocrystals with different morphologies from the reaction of Sm(OA)3 and VO4(TOA)3 complexes in toluene in the presence of surfactant (oleylamine or oleic acid) through a solvothermal pathway. The present solvothermal approach is simple and reproducible and employs a relatively mild reaction temperature. The obtained SmVO4 nanocrystals were characterized by means of transmission electron microscopy, selected area electronic diffraction (SAED), X-ray diffraction (XRD), Elemental dispersive spectrum, X-ray photoelectron spectra (XPS), UV−visible, thermogravimetric differential thermal analysis TGA−DTA, FTIR, and N2 adsorption/desorption isotherms (BET) techniques. The SAED and XRD patterns confirmed that the structure of the synthized SmVO4 nanocrystals is single-crystalline tetragonal. The size, shape, and aspect ratio of products can be readily controlled by adjusting the reaction parameters, such as the nature and amount of surfactant, and the concentration of the metal complex precursors. The SmVO4 nanocrystals with spherical and hexagonal shapes were obtained by using oleylamine or oleic acid as a nonselective and selective surfactant, respectively, under the same synthesis conditions. Furthermore, the average particle size is tunable from 30 to 3 nm by increasing the oleylamine concentration from 0.025 to 0.43 M in the synthesis solution. The shape evolution from nanocores to nanowires can also be obtained by increasing the metal complex precursor concentration; it is associated with the increase in the chemical potential in the reaction solution. The XPS results revealed only one oxidation state for Sm3+ and V5+ on the SmVO4 nanocrystal surface, even after calcinations compared two oxidation states (e.g., Sm2+/Sm3+ and V4+/V5+) of the single samarium oxide and vanadium oxide NPs, respectively. Our synthetic approach can be further extended to the synthesis of other uniform rare earth orthovanadate, molybdate, and tungstate nanocrystals.

Synthesis of SrGa2S4:Mn,Ce and SrGa2S4:Mn,La phosphors by sulfurization of oxide precursors prepared by an amorphous metal complex method and a micro-gel freezing drying process

(Sr0.975Mn0.02Ln0.005)Ga2S4 (Ln = La and Ce) phosphor materials were synthesized by the sulfurization of oxide-carbonate precursors prepared using aqueous solution processes based on amorphous metal complex method or micro-gel freeze-drying method. As a group, multicomponent sulfide phosphors obtained from the amorphous metal complex precursors demonstrated stronger emission brightness than materials of the same composition synthesized by the micro-gel spray freeze-drying method. (Sr0.975Mn0.02Ce0.005)Ga2S4 phosphor demonstrated blue emission intensity reaching 40% intensity of one of the best commercially available BAM phosphors excited by 408 nm light. (Sr0.975Mn0.02La0.005)Ga2S4 red phosphor exhibited strong deep red emission when excited by 310 nm light, and in terms of emission intensity it outperformed Ba1.59Sr0.4ZnS4:Eu2+. Nevertheless, the former material can not be excited by visible or near UV light.

P.243 Blowout fracture in patients with binocular vision impairment

A bis-cyclometallating ligand bearing two different terdentate coordination sites (NCN: dipyridyI-benzene; PCP: diphosphaalkenebenzene moieties) has been synthesised. Selective reactions of appropriate metal complex precursors afforded a heterodinuclear ruthenium(II)-palladium(II) complex characterised by 1H, 13P NMR spectroscopy and FAB-MS techniques. We have compared its electrochemical and spectroscopic properties (absorption and emission) with the individual ruthenium(II) and palladium(II) subunits.

Formation of metallic Ni nanoparticles on titania surfaces by chemical vapor reductive deposition method

Metallic Ni nanoparticles were successfully prepared on the surface of titania thin film substrate by a novel method, named as chemical vapor reductive deposition (CVRD) method. The growth of the nanoparticles was based on the specific adsorption and heterogeneous nucleation on the surface of substrate, not via vapor-phase formation and subsequent sedimentation. The nanoparticle size was found to be well controllable between 10 and 30 nm by the preparation time and vapor pressure of metal complex precursor. ESCA and electron diffraction results clearly demonstrated Ni nanoparticles as metallic. Titania thin film with metallic Ni nanoparticles on its surface showed high efficiency in their photocatalysis of hydrogen evolution from decomposition of ethanol.

Catalyst design for selective oxidation with molecular oxygen by metal-complex attachment

We have prepared novel metal-ensemble catalysts by chemical attachment of metal-complex precursors, N-interstitial Re 10 cluster supported on HZSM-5 and chiral self-dimerized V-dimer on SiO 2, which are active and highly selective for selective oxidation with molecular oxygen. The Re 10(N) 2/HZSM-5 catalyst exhibited 87.7% (steady-state reaction) and 93.9% (pulse reaction) selectivity for direct phenol synthesis from benzene with molecular oxygen. The structures of active metal species were characterized by EXAFS, TPD and DFT calculations. The chiral self-dimerized V-dimer catalyst was found to be the first heterogeneous catalyst for the asymmetric oxidative coupling of 2-naphthol with molecular oxygen, which exhibited 100% selectivity and 90% enantioselectivity.

Controlling Structure from the Bottom-Up: Structural and Optical Properties of Layer-by-Layer Assembled Palladium Coordination-Based Multilayers

Layer-by-layer assembly of two palladium coordination-based multilayers on silicon and glass substrates is presented. The new assemblies consist of rigid-rod chromophores connected by terminal pyridine moieties to palladium centers. Both colloidal palladium and PdCl2(PhCN)2 were used in order to determine the effect of the metal complex precursor on multilayer structure and optical properties. The multilayers were formed by an iterative wet-chemical deposition process at room temperature in air on a siloxane-based template layer. Twelve consecutive deposition steps have been demonstrated resulting in structurally regular assemblies with an equal amount of chromophore and palladium added in each molecular bilayer. The optical intensity characteristics of the metal-organic films are clearly a function of the palladium precursor employed. The colloid-based system has a UV-vis absorption maximum an order of magnitude stronger than that of the PdCl2-based multilayer. The absorption maximum of the PdCl2-based film exhibits a significant red shift of 23 nm with the addition of 12 layers. Remarkably, the structure and physiochemical properties of the submicron scale PdCl2-based structures are determined by the configuration of the approximately 15 angstroms thick template layer. The refractive index of the PdCl2-based film was determined by spectroscopic ellipsometry. Well-defined three-dimensional structures, with a dimension of 5 microm, were obtained using photopatterned template monolayers. The properties and microstructure of the films were studied by UV-vis spectroscopy, spectroscopic ellipsometry, atomic force microscopy (AFM), X-ray reflectivity (XRR), scanning electron microscopy (SEM), and aqueous contact angle measurements (CA).

Ceramic membranes modified with catalytic oxide films as ensembles of catalytic nanoreactors

Hybrid catalytic membrane systems have been produced by modifying porous ceramic membranes with metal oxide films. A two-layer cermet membrane consisting of a flexible stainless steel layer and an overlying porous TiO2 ceramic layer and a ceramic titanium carbide membrane are examined. The membrane surfaces have been modified by the alkoxide method using colloidal organic solutions of metal complex precursors. Producing a tetragonal single-phase ZrO2/Y2O3 coating on the cermet surface increases the abrasion strength of the ceramic layer. CO oxidation and the oxidative conversion of methane into synthesis gas and light hydrocarbons can be markedly intensified by modifying the membrane channels with Cu0.03Ti0.97O2±δ and La + Ce/MgO catalysts, respectively. A method has been developed for depositing, onto the geometrical surface of a membrane, a film of the new single-phase oxide P0.03Ti0.97O2±δ with an anatase structure and uniform pores of mean diameter 〈d〉 ∼ 2 nm. Blocks of zeolite-like silicalite can be formed on the surface of the phosphorus-titanium oxide film. The resulting hybrid membrane is characterized by an anisotropic permeability depending on the flow direction. This property has an effect on conversion and selectivity in the nonoxidative dehydrogenation of methanol.

Polyelectrolyte-Mediated Assembly of Copper-Phthalocyanine Tetrasulfonate Multilayers and the Subsequent Production of Nanoparticulate Copper Oxide Thin Films

An approach to producing films of nanometer-sized copper oxide particulates, based on polyelectrolyte-mediated assembly of the precursor, copper(II)phthalocyanine tetrasulfonate (CPTS), is described. Multilayered CPTS and polydiallyldimethylammonium chloride (PDADMAC) were alternately assembled on different planar substrates via the layer-by-layer (LbL) procedure. The growth of CPTS multilayers was monitored by UV-visible spectrometry and quartz crystal microbalance (QCM) measurements. Both the UV-visible spectra and the QCM data showed that a fixed amount of CPTS could be attached to the substrate surface for a given adsorption cycle. Cyclic voltammograms at the CPTS/PDADMAC-covered gold electrode exhibited a decrease in peak currents with the layer number, indicating that the permeability of CPTS multilayers on the electrodes had diminished. When these CPTS multilayered films were calcined at elevated temperatures, uniform thin films composed of nanoparticulate copper oxide could be produced. Ellipsometry showed that the thickness of copper oxide nanoparticulate films could be precisely tailored by varying the thickness of CPTS multilayer films. The morphology and roughness of CPTS multilayer and copper oxide thin films were characterized by atomic force microscopy. X-ray diffraction (XRD) measurements indicated that these thin films contained both CuO and Cu2O nanoparticles. The preparation of such copper oxide thin films with the use of metal complex precursors represents a new route for the synthesis of inorganic oxide films with a controlled thickness.

Design of catalytic sites at oxide surfaces by metal-complex attaching and molecular imprinting techniques

This paper attempts to summarize our recent studies on the chemical design and characterization of catalytic sites at oxide surfaces such as Nb monomer, dimer and monolayer on SiO 2, Rh dimers on SiO 2, TiO 2, Al 2O 3, and MgO, and Au nanoparticles on TiO 2(1 1 0), prepared by using suitable metal-complex precursors in a molecular scale. The paper also reports performances of new molecular imprinting catalysts, SiO 2 overlayers/α-Al 2O 3 and Rh–SiO 2 overlayers/SiO 2, designed by surface molecular imprinting techniques.