A strategy to find minimal energy nanocluster structures

An unbiased strategy to search for the global and local minimal energy structures of free standing nanoclusters is presented. Our objectives are twofold: to find a diverse set of low lying local minima, as well as the global minimum. To do so, we use massively the fast inertial relaxation engine algorithm as an efficient local minimizer. This procedure turns out to be quite efficient to reach the global minimum, and also most of the local minima. We test the method with the Lennard–Jones (LJ) potential, for which an abundant literature does exist, and obtain novel results, which include a new local minimum for LJ₁₃, 10 new local minima for LJ₁₄, and thousands of new local minima for . Insights on how to choose the initial configurations, analyzing the effectiveness of the method in reaching low‐energy structures, including the global minimum, are developed as a function of the number of atoms of the cluster. Also, a novel characterization of the potential energy surface, analyzing properties of the local minima basins, is provided. The procedure constitutes a promising tool to generate a diverse set of cluster conformations, both two‐ and three‐dimensional, that can be used as an input for refinement by means of ab initio methods. © 2013 Wiley Periodicals, Inc.     

Neutron activation analysis of high purity noble metals (palladium,platinum, rhodium,gold and silver)

Methods of neutron activation analysis of high purity noble metals have been developed based on the selective extraction procedures for matrix activities separation. These procedures are shown to provide purification coefficients from matrix of about 10⁶–10⁸. High-resolution gamma-spectrometry makes possible the determination of 25–30 elements simultaneously in aqueous phases remained after matrix separation. Complex standard for NA analysis of pure materials has been described.     

Ruthenium,rhodium and palladium complexes of pyridines

Summary The syntheses, chemical reactivity, physicochemical properties and applications in solar energy conversion and storage of ruthenium, rhodium and palladium complexes of pyridines are described.     

Particle size determination of platinum, palladium and rhodium

Simple and sufficiently accurate equations are suggested for calculating the particle size of most frequently used supported or unsupported platinum metal catalysts from the amount of chemisorbed gas.

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Acetothioacetanilide as a gravimetric reagent for palladium, platinum and rhodium

Acetothioacetanilide, CH(3)CO . CH(2) . CS . NH . C(6)H(5) is found to be a very suitable gravimetric reagent for Pd(II), Pt(II) and Rh(III). The complexes [composition, M(C(10)H(10)NOS)(2); for M = Pd(II) and Pt(II), and M(C(10)H(10)NOS)(3)] are stable and can be weighed after drying at 105-110 degrees . Separation from base metals has been studied, and a structural interpretation made from DTA, TG and infrared data.     

A new solvent extraction scheme for the separation of platinum,palladium, rhodium and iridium

A new scheme is proposed for the separation of platinum, palladium, rhodium and iridium in hydrochloric acid solutions, by solvent extraction. Platinum and palladium are complexed with 2-mercaptobenzothiazole and potassium iodide and simultaneously extracted into chloroform, thus separating them from rhodium and iridium. Palladium is separated from platinum by extracting its dimethylglyoxime complex into chloroform, while rhodium is separated from iridium by extracting its 2-mercaptobenzothiazole complex into chloroform after reduction with tin(II) chloride.     

A new tripod PPN bridging ligand and its copper,silver and palladium complexes: syntheses,characterizations and X-ray structures

A new tripod bridging ligand 2-{bis(diisopropylphosphino)methyl}-1-methylimidazole, MeImCH(Pi-Pr₂)₂ (PPN) was synthesized conveniently by reacting 2-{bis(trimethylsilyl)methyl}-1-methylimidazole and chlorodiisopropylphosphine. The dicationic dinuclear complex [Cu₂(PPN)₂][ClO₄]₂ (1) was prepared by the reaction of the ligand with [Cu(MeCN)₄]ClO₄ in acetonitrile. The reaction of the ligand with AgNO₃ in propane-2-ol followed by addition of NH₄PF₆ led to the formation of a similar type complex [Ag₂(PPN)₂][PF₆]₂ (2). The X-ray diffraction studies of 1 and 2 revealed a μ₂-η¹:η² tripod-like bonding of the PPN ligand, with one P and one N atom chelating to one metal ion and the remaining one P atom binds to another metal ion, affording a face-to-face type molecule. An eight-membered M₂P₄C₂ and a 10-membered M₂P₂N₂C₄ ring are thus formed with this new functional diphosphine ligand. In both complexes the two metal ions are held in very close proximity [2.6707 Å for 1 and 2.859(3) Å for 2]. Complex 1 underwent a rapid ligand exchange process in solution. Besides these dinuclear complexes the ligand also afforded a mononuclear palladium complex, [PdCl₂(PPN)] (3), when it was treated with an equimolar amount of [PdCl₂(PhCN)₂] in benzene. In 3 the ligand acts as a bidentate chelate through its two phosphorus atoms, leaving the imidazole donor dangling. On the other hand, a P,P-bridged dinuclear Pd(I) complex [Pd₂Cl₂(PPN)₂] (4) was achieved by reacting two moles of the ligand with one mole of [PdCl₂(PhCN)₂], followed by the addition of one mole of Pd(dba)₂ [dba=dibenzylideneacetone].     

Neutron activation analysis for iridium,palladium and silver in platinum

A sensitive procedure for the simultaneous determination of trace levels of iridium, palladium and silver in a platinum stock, by thermal-neutron activation analysis utilizing gamma-ray spectrometry, was developed. The radiochemical-separation scheme involved an elution of the chloro complexes of iridium and silver, and subsequently palladium, through a strongly-basic anion-exchange resin, followed by further chemical-separation methods. The ion-exchange method served to greatly reduce the hazard from radiations emitted by the bulk of the activities in the matrix. Activities of 13.5-hr¹⁰⁹Pd, 74.2-d¹⁹²Ir and 255-d^110m Ag were monitored by accumulation of pulses from a 3-in diam. NaI(T1) crystal detector. Further discrimination was attained by resolution of decay curves. The procedure provided analyses for a platinum stock of 0.015±0.0021 ppm Ir; 0.028±0.0043 ppm Pd and 2.4±0.27 ppm Ag.     

Structure of supported palladium,silver and gold clusters

Clusters nucleated by inert gas aggregation have been studied by HREM. The clusters were supported by amorphous carbon films and by crystalline graphite fibres. Multiply twinned particles with 5-fold axes of symmetry were observed whose structures and orientations are discussed. It is also demonstrated that crystalline graphite substrates can be used to calibrate lattice distances and to improve the image processing. With the help of computer simulations complex structures were resolved.     

Neutron activation analysis of palladium,platinum and rhodium in lead foam

The determination of palladium, platinum and rhodium in industrial concentrates such as lead foam and raw lead by neutron activation analysis is described. The noble elements are separated from the matrix by spontaneous deposition on amalgamated copper powder prior to activation. After the determination of palladium and platinum, rhodium is coprecipitated on iron hydroxide, and the precipitate irradiated for the determination of rhodium. The results are compared with those obtained by fire assay. Research Associate of I.I.K.W., Belgium.     

A solvent-extraction scheme for the determination of platinum,palladium, rhodium,iridium and gold in platiniferous materials

The integrated scheme described for the determination of five noble metals, combines solvent extraction procedures with atomic absorption spectrometric finishes. It comprises an initial extraction of gold, a simultaneous extraction of platinum and palladium as iodides, and a subsequent simultaneous extraction and preconcentration of rhodium and indium as their 2-mercaptobenzothiazol? complexes. The same solvent, methyl isobutyl ketone, and the same acidity, 6 M, are used throughout the extractions. As large amounts of platinum and palladium can be extracted quantitatively as readily as small amounts, the proposed scheme is applicable to a wide range of platiniferous materials, particularly to those with extremely high Pt + Pd to Rh + Ir ratios.     

Reductive coprecipitation as a separation method for the determination of gold,palladium, platinum,rhodium, silver,selenium and tellurium in geological samples by graphite furnace atomic absorption spectrometry

A method for the separation of Au, Pd, Pt, Rh, Ag, Te and Se from geological samples at trace levels is presented. The elements are separated from the matrix after dissolution by reductive coprecipitation using mercury as a collector and tin(II) chloride as a reductant. The efficiency of coprecipitation is studied by varying the acidity of the solutions and the amount of collector. The analyte elements are determined by graphite furnace atomic absorption spectrometry. In the determination of volatile elements (Te, Au and Ag), matrix modification with iridium is used. Selenium is determined with a mixed matrix modifier containing ascorbic acid and iridium. The method is tested by analysing geochemical reference samples.     

Microwave-assisted aqua regia digestion for determining platinum,palladium, rhodium and lead in catalyst materials

This study investigated a microwave-assisted aqua regia digestion of catalyst samples prior to the determination of Pt, Pd, Rh and Pb by ICP-OES. While optimising the method, the effect of digestion temperature on the digestion efficiency was investigated. Few aqua regia digestions were also carried out using a high pressure asher, with a digestion temperature of 280 °C. In addition, XRD (X-ray diffractometry) was used to characterise digestion residue. The study showed that accurate and reliable results for Pt, Pd, Rh and Pb in a recycled monolith catalyst (NIST SRM 2557) were obtained by ICP-OES after the microwave assisted aqua regia digestion. The amounts of Pt, Pd and Rh in the prepared catalyst samples were also at the expected levels. Furthermore, the results indicated that the main part of the impurities and supporting material elements can be quantitatively extracted from the catalyst samples by using the microwave-assisted aqua regia sample pre-treatment.     

Some new transformations of cyclopropylacetylene catalyzed by rhodium,palladium, and cobalt complexes

The linearand cyclic dimerization and trimerization of cyclopropylacetylene were carried out by the action of rhodium, palladium, and cobalt catalysts to give 2,4-dicyclopropyl-1-buten-3-yne, 1,3,6-tricyclopropylfulvene, and 1,3,5-and 1,2,4-tricyclopropylbenzenes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2360–2362, October, 1989.     

Synthesis and investigation of mono- and binuclear cyano-bridged complexes of rhodium,ruthenium, and palladium

Binuclear Rh^III and Ru^II complexes of the [M¹-CN-M²]⁺BF ₄ ^– (M¹ and/or M² are (⁵-Cp)(³-C₃H₅)Rh and (⁶-C₆H₆)(³-C₃H₅)Ru) type, heteronuclear organometallic compound (⁵-Cp)(³-C₃H₅)RhCNPd(³-C₃H₅)Cl, and mononuclear Rh^III and Ru^II complexes [(³-C₃H₅)LM(MeCN)]⁺ _BF4 ^– (M = Rh, L = ⁵-Cp; M = Ru, L = ⁶-C₆H₆) were synthesized. An electrochemical study of these compounds in solutions demonstrates that the bond between the bridged CN ligand and the metal atoms is rather strong, and there is no dissociation into mononuclear fragments in solutions. The kinetics of the reaction of [(⁵-Cp)(³-C₃H₅)Rh(MeCN)]⁺ _BF4 ^– with halide ions was studied by electrochemical methods. The ligand exchange proceeds by a bimolecular dissociative-exchange mechanism.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 968–973, May, 1995.