Die thermodynamische Stabilität der Molekeln Pd6Cl12, Pd6Br12 und Pt6Cl12

Thermodynamic Stability of Pd₆Cl₁₂, Pd₆Br₁₂, and Pt₆Cl₁₂ Molecules Vapour pressure data of PdCl₂ and PdBr₂ taken from the literature have been used to get new informations regarding the vapourization of Pd₆Cl₁₂ molecules. Using mixtures of PdCl₂ and AgBr as source materials, besides Pd₆Cl₁₂ molecules the vapourization of Pd₆Cl_12-nBr_n with n = 1 – 8 has been observed in a mass spectrometer. Semi quantitative observations concerning the vapourization of Pt₆Cl₁₂ molecules from a PtCl₂ solid are reported. Heats of formation and standard entropy data for the molecules Pd₆Cl₁₂, Pd₆Br₁₂ and Pt₆Cl₁₂ are given.     

DFT studies of the characteristics of Pd−Pt core-shell clusters

It is reported that Pd?Pt core-shell type nanoclusters in which the inner atoms of the Pd cluster are substituted by Pt significantly enhance the catalytic activity for cycloocatdiene hydrogenation. In order to discuss the electronic states of core-shell clusters, DFT calculations were carried out for Pd₁₃, Pt₁₃, Pt/Pd₁₂, Pd/Pt₁₂ Pd₃₈ and Pd₆/Pt₃₂ clusters. From these calculations, it was found that the charge transfer between the core atoms and the shell atoms played an important role for the modification of the electronic state of the surface atoms in them.     

195Pt-NMR-spektroskopischer Nachweis gemischter Hexahalogenodiplatinate(II), [Pt2ClnBr6 − n]2−, n = 0 – 6

¹⁹⁵Pt NMR Spectroscopic Evidence of Mixed Hexahalogenodiplatinates(II), [Pt₂Cl_nBr_{6 ? n}]^2?, n = 0 – 6 The complete system of the mixed complex ions [¹⁹⁵Pt₂Cl_nBr_{6 – n}]^2?, n = 0 – 6, is formed by stirring a suspension of the tetrabutylammonium salt(TBA)₂[¹⁹⁵PtCl₄] in an aqueous solution of KBr at 80°C. The mixture recrystallized from acetone/diethyl ether contains the 24 possible species, 12 with two equivalent ¹⁹⁵Pt atoms resulting in 12 singlets and 12 with inequivalent ¹⁹⁵Pt atoms resulting in 24 dublets. The expected 60 signals are really observed in the high resolution 1D-¹⁹⁵Pt-nmr spectrum. Using characteristic increments of chemical shifts, differentiating ²J(¹⁹⁵Pt ? ¹⁹⁵Pt) coupling constants and a 2D-¹⁹⁵Pt/¹⁹⁵Pt-COSY spectrum the complete and unambiguous assignment of all resonances is achieved. The presence of all components including the geometric isomers and their distribution derived from measured intensities reveal the statistical formation.     

Thermal decomposition of nickel(II), palladium(II), and platinum(II) complexes of <Emphasis Type="Italic">N</Emphasis>-allyl-<Emphasis Type="Italic">N</Emphasis>′-pyrimidin-2ylthiourea

Thermal decomposition of Ni(II), Pd(II), and Pt(II) complexes of N-pyrimidin-2ylthiourea (AllPmTu) have been studied by TG, DTG, and DTA and by electron impact (EI) mass spectra. The complexes have the molecular formulae as [Ni(AllPmTu)Cl₂(H₂O)], [Ni(AllPmTu)₂Cl₂(H₂O)₂], and [M(AllPmTu)Cl₂], where M = Pd^II or Pt^II, and [Pt(AllPmTu)₂]. The TG curves show that Ni(II) complexes decompose in three stages to yield NiO as a residue, while Pd(II) and Pt(II) decompose in two stages to yield MS residues. The initial mass losses correspond to elimination of allylamine for Pd(II) and Pt(II) complexes but, allyisothiocyanate for both Ni(II) complexes revealing that sulfur atom of thiourea part is involved in coordination to Pd(II) and Pt(II) but does not to Ni(II). Kinetic parameters (E ^#, n, ΔH ^#, ΔS ^#, ΔG ^#) of the decomposition stages are determined and correlated with bonding and structural properties of the complexes. The EI mass spectra of the complexes show fragments corresponding to the evolved and intermediate species.     

Coordination compounds of 2-mercapto-1-methylimidazole with platinum(II), palladium(II), rhodium(III) and ruthenium(III)

Summary Complexes of 2-mercapto-1-methylimidazole (TMZ) with Pt^II, Pd^II, Rh^III and Ru^III of the general formulae Pt(TMZ)₂Cl₂, Pd(TMZ)₄Cl₂. Rh(TMZ)Cl₃ and Ru(TMZ)Cl₃ have been obtained. The thermal stabilities of the compounds were estimated by derivatographic measurements and the electron-donating atom of the measurements and the electron-donating atom of the ligand was identified from the i.r. absorbtion spectra. Lattice constants for the Pt^II and Pd^II complexes were estimated from their x-ray powder diffraction patterns.     

Synthesen,Eigenschaften und Kristallstrukturen der Cluster‐Salze Bi6[PtBi6Cl12] und Bi2/3[PtBi6Cl12]

Syntheses, Properties and Crystal Structures of the Cluster Salts Bi₆[PtBi₆Cl₁₂] and Bi_2/3[PtBi₆Cl₁₂] Melting reactions of Bi with Pt and BiCl₃ yield shiny black, air insensitive crystals of the subchlorides Bi₆[PtBi₆Cl₁₂] and Bi_2/3[PtBi₆Cl₁₂]. Despite the substantial difference in the bismuth content the two compounds have almost the same pseudo‐cubic unit cell and follow the structural principle of a CsCl type cluster salt. Bi₆[PtBi₆Cl₁₂] consists of cuboctahedral [PtBi₆Cl₁₂]^2? clusters and Bi₆²⁺ polycations (a = 9.052(2) Å, α = 89.88(2)°, space group P 1, multiple twins). In the electron precise cluster anion, the Pt atom (18 electron count) centers an octahedron of Bi atoms whose edges are bridged by chlorine atoms. The Bi₆²⁺ cation, a nido cluster with 16 skeletal electrons, has the shape of a distorted octahedron with an opened edge. In Bi_2/3[PtBi₆Cl₁₂] the anion charge is compensated by weakly coordinating Bi³⁺ cations which are distributed statistically over two crystallographic positions (a = 9.048(2) Å, α = 90.44(3)°, space group ). Bi₆[PtBi₆Cl₁₂] is a semiconductor with a band gap of about 0.1 eV. The compound is diamagnetic at room temperature though a small paramagnetic contribution appears towards lower temperature.     

Alloyed Tetranuclear Metal Chains of Pd4−nPtn (n=0–3) Scaffolded by a New Linear Tetraphosphine Containing a PNP Bridge

A new linear tetraphosphine containing a PNP phosphazane bridge, rac-bis[(diphenylphosphinomethyl)phenylphosphino]phenylamine (rac-dpmppan), was synthesized and utilized to support a series of Pd/Pt mixed metal tetranuclear chains, [Pd_4−nPt_n(μ-rac-dpmppan)₂(XylNC)₂](PF₆)₂ (XylNC=xylyl isocyanide; n=0: Pd₄ ( 1 ), 1: PtPd₃ ( 2 ), 2: PtPd₂Pt ( 3 ), 2: Pt₂Pd₂ ( 4 ), 3: Pt₂PdPt ( 5 )), in which the number and positions of additional Pt atoms were successfully controlled depending on the respective synthetic procedures using transformations from 1 to 3 through 2 and from 4 to 5 by redox-coupled exchange reactions. The ³¹P{¹H} NMR and ESI mass spectra and X-ray diffraction analyses revealed almost identical tetranuclear structures, with slight contraction of metal-metal bonds according to incorporation of Pt atoms. The electronic absorption spectra of 1 – 5 exhibited characteristic bands at 635–510 nm with an energy propensity depending on the number and positions of Pt centres, which were assigned to HOMO (dσ*σσ*) to LUMO (dσ*σ*σ*) transition by theoretical calculations. The present results demonstrated that the electronic structures of Pd/Pt mixed-metal tetranuclear complexes are finely tuned as orbital-overlapping alloyed metal chains by atomically precise Pt incorporation in the Pd₄ chain.     

Zur Kenntnis von Ba6Ru2PtO12Cl2

About Ba₆Ru₂PtO₁₂Cl₂ Single crystals of Ba₆Ru₂PtO₁₂Cl₁₂ were prepared by a BaCl₂ flux and investigated by X-ray methods (D? P3 M1; a = 5,805; c = 15.006 Å; Z = 1). The characteristic face shared M₃O₁₂-octahedratriples show an ordered (Ru/Pt/Ru) occupation. Calculation of the Coulomb term of lattice energy support the charge distribution (5⁺/4⁺/5⁺) ions engage three point sites with different coordinations. The connection to other compounds are discussed.     

One-Pot Synthesis of Pd@PtnL Core-Shell Icosahedral Nanocrystals in High Throughput through a Quantitative Analysis of the Reduction Kinetics

The rational design and implementation of a one-pot method is reported for the facile synthesis of Pd@Pt_nL (nL denotes the number of Pt atomic layers) core-shell icosahedral nanocrystals in a single step. The success of this method relies on the use of Na₂PdCl₄ and Pt(acac)₂ as the precursors to Pd and Pt atoms, respectively. Our quantitative analysis of the reduction kinetics indicates that the Pd^II and Pt^II precursors are sequentially reduced with a major gap between the two events. Specifically, the Pd^II precursor is reduced first, leading to the formation of Pd-based icosahedral seeds with a multiply-twinned structure. In contrast, the Pt^II precursor prefers to take a surface reduction pathway on the just-formed icosahedral seeds. As such, the otherwise extremely slow reduction of the Pt^II precursor can be dramatically accelerated through an autocatalytic process for the deposition of Pt atoms as a conformal shell on each Pd icosahedral core. Compared to the conventional approach of seed-mediated growth, the throughput for the one-pot synthesis of Pd@Pt_nL core-shell nanocrystals can be increased by more than 30-fold. When used as catalysts, the Pd@Pt_4.5L core-shell icosahedral nanocrystals show specific and mass activities of 0.83 mA cm⁻² and 0.39 A mg_Pt⁻¹, respectively, at 0.9 V toward oxygen reduction. The Pt-based nanocages derived from the core-shell nanocrystals also show enhanced specific (1.45 mA cm⁻²) and mass activities (0.75 A mg_Pt⁻¹) at 0.9 V, which are 3.8 and 3.3 times greater than those of the commercial Pt/C, respectively.     

Palladium(II) and Platinum(II) Complexes of N-Phenyl- and N-Ethyl-N′-pyrimidin-2-ylthiourea

Palladium(II) and platinum(II) complexes of N-ethyl-N′-pyrimidin-2-ylthiourea(HL¹) and N-phenyl-N′-pyrimidin-2-ylthiourea (HL²) have been prepared, and the complexes [M(HL)Cl₂], [Pt(L)₂], [Pd(HL¹)₂]Cl₂, and [Pd(L²)₂] (where M = Pd^II or Pt^II) were characterized. The spectroscopic data are consistent with coordination of thioureas as neutral or monoanionic ligands to Pd^II and Pt^II through S and a pyrimidine-N. The IR spectra show shifts of CS and pyrimidine ring stretch bands to lower and higher frequencies, respectively. The ¹H NMR spectra differentiate between H(4′) and H(6′) resonances and indicate downfield shifts for all protons of pyrimidine [H(4′), H(5′), and H(6′)], two resonances for two N?H protons for complexes containing the neutral ligand (HL), and only one N?H proton chemical shift for complexes containing the monoanion (L). ¹³C NMR chemical shifts of pyrimidine carbons are correlated with the type of bonding between Pd^II or Pt^II and pyrimidine-N. The magnetic susceptibilities suggest a diamagnetic planar structure for all complexes.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

萘在贵金属Pd、Pt及Pd-Pt催化剂上的加氢活性及耐硫性能

采用等体积浸渍法制备了SiO2-Al2O3负载的Pd、Pt单金属催化剂及Pd/Pt摩尔比分别为1∶1、1∶4、4∶1的双金属催化剂(Pd1Pt1、Pd1Pt4、Pd4Pt1),对其进行X射线衍射(XRD)、透射电镜(TEM)、CO化学吸附和X射线光电子能谱(XPS)表征,并详细考察了各催化剂的萘加氢活性和耐硫性能.结果表明,在实验考察范围内,Pd4Pt1催化剂上的萘转化率最高可达98.2%,全饱和产物十氢萘选择性最高可达93.6%,十氢萘反/顺生成率之比最高可达7.8,均高于单金属Pd(97.5%,59.1%,4.3)和Pt(96.8%,39.9%,2.9)催化剂的值.萘在三种催化剂上的加氢速率顺序为vPd4Pt1vPdvPt.添加二苯并噻吩(DBT)后Pd4Pt1上的萘转化率和十氢萘选择性仍然最高,十氢萘反/顺比在Pt催化剂上不受影响,在Pd4Pt1催化剂上稍有降低,而在Pd催化剂上降低明显.在三种不同Pd/Pt摩尔比的双金属催化剂中,Pd4Pt1催化剂上的萘转化率和十氢萘选择性在添加DBT前后都是最佳的.     

Can Serendipity Still Hold Any Surprises in the Coordination Chemistry of Mixed-Donor Macrocyclic ligands? The Case Study of Pyridine-Containing 12-Membered Macrocycles and Platinum Group Metal ions PdII,PtII, and RhIII

This study investigates the coordination chemistry of the tetradentate pyridine-containing 12-membered macrocycles L¹-L³ towards Platinum Group metal ions Pd^II, Pt^II, and Rh^III. The reactions between the chloride salts of these metal ions and the three ligands in MeCN/H₂O or MeOH/H₂O (1:1 v/v) are shown, and the isolated solid compounds are characterized, where possible, by mass spectroscopy and ¹H- and ¹³C-NMR spectroscopic measurements. Structural characterization of the 1:1 metal-to-ligand complexes [Pd(L¹)Cl]₂[Pd₂Cl₆], [Pt(L¹)Cl](BF₄), [Rh(L¹)Cl₂](PF₆), and [Rh(L³)Cl₂](BF₄)·MeCN shows the coordinated macrocyclic ligands adopting a folded conformation, and occupying four coordination sites of a distorted square-based pyramidal and octahedral coordination environment for the Pd^II/Pt^II, and Rh^III complexes, respectively. The remaining coordination site(s) are occupied by chlorido ligands. The reaction of L₃ with PtCl₂ in MeCN/H₂O gave by serendipity the complex [Pt(L³)(μ-1,3-MeCONH)PtCl(MeCN)](BF₄)₂·H₂O, in which two metal centers are bridged by an amidate ligand at a Pt1-Pt2 distance of 2.5798(3) Å and feature one square-planar and one octahedral coordination environment. Density Functional Theory (DFT) calculations, which utilize the broken symmetry approach (DFT-BS), indicate a singlet d⁸-d⁸ Pt^II-Pt^II ground-state nature for this compound, rather than the alleged d⁹-d⁷ Pt^I-Pt^III mixed-valence character reported for related dinuclear Pt-complexes.     

Die Fällung des PdII als [Pd(NH3)2Cl2] sowie das Verhalten verschiedener Begleitelemente

Precipitation of Pd^II as [Pd(NH₃)₂Cl₂] and the Behaviour of Various Impurities The dependence of [Pd(NH₃)₂Cl₂] precipitation upon reaction conditions (pH, Cl^? content, reaction time, temperature) has been studied. The dependence of residual Pd content in the mother liquor upon these parameters was found to be significant only for the precipitation temperature (c_Pd at 20°C: 1.65 ± 0.11 mM; at 50°C: 6.70 ± 0.58 mM). The increase of Pd concentration was due to the formation of Pd(NH₃)Cl₃^?. Among the impurities studied Cr, Ru, and Au were largely precipitated in the NH₃ medium. In subsequent precipitation of [Pd(NH₃)₂Cl₂] the following order of coprecipitation was found: The first four elements could be separated only incompletely by repeated reprecipitation. The coprecipitation of the platinum-group metals and of Au was highly dependence upon preceding formation of ammine complexes of these elements. The considerable coprecipitation of Pt^IV is presumably due to the formation of mixed Pd/Pt compounds, whereas the other impurities are adsorbed by [Pd(NH₃)₂Cl₂].     

Metalizing carbon nanotubes with Pd–Pt core–shell nanowires enhances electrocatalytic activity and stability in the oxygen reduction reaction

We describe an electrostatically induced self-assembly method to prepare ultrathin Pd nanowires (NWs) surrounding individual multiwalled carbon nanotubes, i.e., Pd_NW/MWNTs, that are noticeable for improving performance in the oxygen reduction reaction (ORR) of their supported Pt_ML electrocatalyst. The carbonaceous by-products in MWNTs, rather than the nanotubes themselves, are modified with the oxygenated terminals to allow the negatively charged and hydrophilic surface while retaining the intrinsic nature of the MWNTs. Encompassing the nanotubes' length are 2-nm-thick Pd NWs that are closely packed and homogeneously dispersed due to the unique processes for preparing Pd_NW/MWNTs and its components. Although the crystal lattice of the Pd NWs expands somewhat, which should cause an unfavorable interaction with supported Pt_ML, this adverse effect is counterweighed by the shape-determined features of Pd NWs, including their high specific surface area, excellent contiguousness, and low-energy atomic configuration. Consequently, these distinct chemical and physical properties substantially expedite the desorption of the intermediates to refresh the active centers during the reduction of oxygen with the Pt_ML electrocatalyst while ensuring a desirable electron transfer rate, so improving the overall ORR kinetics. Indeed, Pt_ML/Pd_NW/MWNTs exhibits the Pt mass and specific activities of 1.45 A/mg_Pt and 0.65 mA/cm² _Pt, respectively, each of which are several times those of the Pt/C and even higher than those of the Pt_ML supported on Pd nanoparticles. These high activities remained over a long-term stability test using the latest US Department of Energy-established protocol.     

Synthesis and structures of Sc7Cl12 and Zr6Cl15

The indicated nine-electron clusters of scandium and zirconium are formed in transport reactions at 880/900°C and 750/600°C, respectively. Sc₇Cl₁₂ (R¯3, a – 12.959(2), c – 8.825(2), Z – 3) can be described as c.c.p. Sc₆Cl₁₂ clusters with isolated metal atoms in all octahedral interstices or as Sc³⁺(Sc₆Cl₆ⁱCl₆^i?a) ^3? with Sc³⁺ in Clⁱ octahedra between Sc₆Cl sheets. Metal-metal distances within the cluster are 3.201?3.230(2) Å. Zr₆Cl₁₂ⁱCl crystallizes in the Ta₆Cl₁₅ structure (Ia3d, a – 21.141(3) Å, Z – 16) with d(Zr? Zr) = 3,199–3.214(4) Å. Apparent residual electron density is found in the center of both clusters, amounting to Z～7.6 (Sc) and ～6 (Zr) based of refinement of oxygen in these positions. The effect is thought to probably arise from errors in the diffraction data rather than partial incorporation of light nonmetal atoms such as oxygen or fluorine. Observed metal-metal distances are compared with those in other clusters.     

Bromsulfenyl(trihalogen)phosphonium-Salze Cl3−nBrnPSBr+AsF6− (n = 0 – 3) und Cl3PSBr+SbF6− — Oxidative Bromierung von Thiophosphorylhalogeniden

Bromosulfenyl(trihalogeno)phosphonium Salts Cl_3?nBr_nPSBr⁺AsF₆^? (n = 0 – 3) and Cl₃PSBr⁺SbF₆^? — Oxidative Bromination of Thiophosphorylhalides The bromosulfenyl(trihalogeno)phosphonium salts Cl_3?nBr_nPSBr⁺AsF₆^? (n = 0 – 3) and Cl₃PSBr⁺SbF₆^? are prepared by oxidative bromination of the corresponding thiophosphorylhalides with Br₂/MF₅ (M = As, Sb) and characterized by vibrational and NMR spectroscopy.     

Structure and Bonding of the Hexameric Platinum(II) Dichloride,Pt6Cl12 (β‐PtCl2)

The crystal structure of Pt₆Cl₁₂ (β‐PtCl₂) was redetermined ( a_h = 13.126Å, c_h = 8.666Å, Z = 3; a_rh = 8.110Å, α = 108.04°; 367 hkl, R = 0.032). As has been shown earlier, the structure is in principle a hierarchical variant of the cubic structure type of tungsten (bcc), which atoms are replaced by the hexameric Pt₆Cl₁₂ molecules. Due to the 60° rotation of the cuboctahedral clusters about one of the trigonal axes, the symmetry is reduced from to ( ). The molecule Pt₆Cl₁₂ shows the (trigonally elongated) structure of the classic M₆X₁₂ cluster compounds with (distorted) square‐planar PtCl₄ fragments, however without metal‐metal bonds. The Pt atoms are shifted outside the Cl₁₂ cuboctahedron by Δ = +0.046Å ( (Pt—Cl) = 2.315Å; (Pt—Pt) = 3.339Å). The scalar relativistic DFT calculations results in the full symmetry for the optimized structure of the isolated molecule with d(Pt—Cl) = 2.381Å, d(Pt—Pt) = 3.468Å and Δ = +0.072Å. The electron distribution of the Pt‐Pt antibonding HOMO exhibits an outwards‐directed asymmetry perpendicular to the PtCl₄ fragments, that plays the decisive role for the cluster packing in the crystal. A comparative study of the Electron Localization Function with the hypothetical trans‐(Nb₂Zr₄)Cl₁₂ molecule shows the distinct differences between Pt₆Cl₁₂ and clusters with metal‐metal bonding. Due to the characteristic electronic structure, the crystal structure of Pt₆Cl₁₂ in space group is an optimal one, which results from comparison with rhombohedral Zr₆I₁₂ and a cubic bcc arrangement.     

Solvolysis of palladium(II) and platinum(II) complexes of asymmetric ligands: Synthesis and structural characterization of [Pd(AMP)(dmso)Cl]BF4 and [Pt(AMP)(dmso)Cl]ClO4

Treatment of [M(AMP)Cl₂] (M = Pt^II, Pd^II; AMP = 2-aminomethylpyridine) with 1 mole of AgX (X = ClO₄, BF₄, PF₆) in dmso yields [M(AMP)(dmso)Cl]X. Single crystal X-ray structure determinations of the Pd^II and Pt^II complexes indicate that dmso is S-bondedtrans to the pyridyl ring in both complexes. (2-Aminomethylpyridine)chloro(dimethylsulphoxide-S) palladium(II) tetrafluoroborate.     

Addition of protic molecules to coordinated 2-pyridinecarboxaldehyde in gold(III), palladium(II), and platinum(II) complexes

The reactions of Au^III, Pt^II and Pd^II complexes with 2-pyridinecarboxaldehyde (2CHO-py) have been examined in protic (H₂O, MeOH, EtOH) and aprotic (DMF, CH₂Cl₂) solvents. Compounds in which the pyridine ligand is N-coordinated, either in the original aldehydic form or in a new form derived from addition of one or two protic molecules, have been isolated, namely: [Au(2CHO-py · H₂O)Cl₃], [Au(2CHO-py · MeOH)Cl₃], [Au(2CHO-py · 2EtOH)Cl₃], cis-[Pt(2CHO-py)₂Cl₂], trans-[Pd(2CHO-py)₂Cl₂], trans-[Pt(dmso)(2CHO-py)Cl₂], [Pt{C₅H₄N-(CH₂SMe)}Cl(2CHO-py)](ClO₄), [Pt(terpy)(2CHOpy)](ClO₄)₂, [Pt(terpy)(2CHO-py · H₂O)](ClO₄)₂ (terpy = 2,2′:6′,2′′-terpyridine). ¹H-n.m.r. experiments show that the addition of the protic molecule(s) to the Pt^II and Pd^II complexes is reversible. The effects of the nature of the metal ion and the ancillary ligands as well as of the total charge of the complexes on the relative stability of the addition products are discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Pt6Cl12·(1,2,4‐C6H3Cl3), a Structurally Characterized Cocrystallization Product of Pt6Cl12

The reaction of platinum(II) chloride with 1,2,4‐trichlorobenzene gives the novel platinum complex Pt₆Cl₁₂·(1,2,4‐C₆H₃Cl₃). It is the first example of an cocrystallization product of platinum(II) chloride and organic molecules whose crystal structure has been established.