Studies of surface processes of electrocatalytic reduction of CO_2 on Pt(210), Pt(310) and Pt(510)

Surface processes of CO2 reduction on Pt(210), Pt(310), and Pt(510) electrodes were studied by cyclic voltammetry. Different surface structures of these platinum single crystal electrodes were obtained by various treatment conditions. The experimental results illustrated that the electrocatalytic activity of Pt single crystal electrodes towards CO2 reduction is decreased in an order of Pt(210)>Pt(310)>Pt(510), i.e., with the decrease of (110) step density on well-defined surfaces. When the surfaces were reconstructed due to oxygen adsorption, the catalytic activity of all the three electrodes has been enhanced to a cer- tain extent. Although the activity order remains unchanged, the electrocatalytic activity has been en- hanced more significantly as the density of (110) step sites is more intensive on the Pt single crystal surface. It has revealed that the more open the surface structure is, the more active the Pt single crystal electrode will be, and the easier for the electrode to be transformed into a surface structure that exhib- its higher activity under external inductions. However, the relatively ordered surfaces of Pt single crystal electrode are comparatively stable under the same external inductions. The present study has gained knowledge on the interaction between CO2 and Pt single crystal electrode surfaces at a micro- scopic level, and thrown new insight into understanding the surface processes of electrocatalytic re- duction of CO2.     

Theoretical study on the charge transport property of Pt(CN(t)Bu)2(CN)2 nanowires induced by Pt···Pt interactions

To deeply understand the charge-transporting nature of Pt(CN(t)Bu)(2)(CN)(2) nanowires induced by intermolecular Pt···Pt interactions, calculations based on first-principle band structure and Marcus theory have been performed. The calculated bandwidths of the valence band, conducting band, and the effective masses of hole and electron are almost equal. This suggests that this complex has ambipolar transport characteristics, in agreement with experimental results. Density of states analysis revealed that the hole transport resulted mainly from the Pt···Pt interactions, while the electron transport was derived mainly from the CN groups. The character of the frontier molecular orbitals, reorganization energies and transfer integrals in different directions also supports the calculated first-principle band structure. Moreover, an investigation into the intermolecular interaction energy of neighbors revealed that there is a remarkable relationship between the intermolecular interaction energy and the transfer integral.     

Studies pertaining to the mechanism of “Pt(PCy3)“ addition. The reaction of MPt(μ-H)(μ-PnPr2)Pt(CO)(PCy3) with Pt(C2H4)2(PCy3)

The reaction of Pt(C₂H₄)₂(PCy₃) with (OC)₄M(μ-H)(μ-PⁿPr₂)Pt(CO)(PCy₃, (1: M  Cr, Mo, W) occurs in a highly specific, kinetically controlled manner to give MPt₂(μ²_MPt-CO)(η²_PtPt-H)(μ²_MPt-PⁿPr₂)(CO)₄ (PCy₃)₂ (5), as the first formed trimer. The trimer 5 (M  Mo, W) isomerizes to give MPt₂(μ²_PtPt-CO) ((μ²_MPtH)(μ²_MPt-PⁿPr₂)(CO)₄)PCy₃)₂ (6) which in turn isomerizes to MPt₂μ²_MPtCO)(μ²_MPt (μ²_PtPt-PⁿPr₂)(CO)₄(PCy₃)₂ (7, as the final isolable product. These results provide a detailed insight into the mechanism of “Pt(PCy₃) addition”, a cluster assembly process.     

Structures of Pd(CN)2 and Pt(CN)2: intrinsically nanocrystalline materials?

Analysis and modeling of X-ray and neutron Bragg and total diffraction data show that the compounds referred to in the literature as "Pd(CN)(2)" and "Pt(CN)(2)" are nanocrystalline materials containing small sheets of vertex-sharing square-planar M(CN)(4) units, layered in a disordered manner with an intersheet separation of ~3.44 ? at 300 K. The small size of the crystallites means that the sheets' edges form a significant fraction of each material. The Pd(CN)(2) nanocrystallites studied using total neutron diffraction are terminated by water and the Pt(CN)(2) nanocrystallites by ammonia, in place of half of the terminal cyanide groups, thus maintaining charge neutrality. The neutron samples contain sheets of approximate dimensions 30 ? × 30 ?. For sheets of the size we describe, our structural models predict compositions of Pd(CN)(2)·xH(2)O and Pt(CN)(2)·yNH(3) (x ≈ y ≈ 0.29). These values are in good agreement with those obtained from total neutron diffraction and thermal analysis, and are also supported by infrared and Raman spectroscopy measurements. It is also possible to prepare related compounds Pd(CN)(2)·pNH(3) and Pt(CN)(2)·qH(2)O, in which the terminating groups are exchanged. Additional samples showing sheet sizes in the range ~10 ? × 10 ? (y ~ 0.67) to ~80 ? × 80 ? (p = q ~ 0.12), as determined by X-ray diffraction, have been prepared. The related mixed-metal phase, Pd(1/2)Pt(1/2)(CN)(2)·qH(2)O (q ~ 0.50), is also nanocrystalline (sheet size ~15 ? × 15 ?). In all cases, the interiors of the sheets are isostructural with those found in Ni(CN)(2). Removal of the final traces of water or ammonia by heating results in decomposition of the compounds to Pd and Pt metal, or in the case of the mixed-metal cyanide, the alloy, Pd(1/2)Pt(1/2), making it impossible to prepare the simple cyanides, Pd(CN)(2), Pt(CN)(2), or Pd(1/2)Pt(1/2)(CN)(2), by this method.     

Study of Hydrogen Adsorption on Pt/WO3-ZrO2 through Pt Sites

The rate determining step and the energy barrier involved in hydrogen adsorption on Pt/WO_3- ZrO_2 were studied based on the assumption that the hydrogen adsorption occurs only through Pt sites. The rate of hydrogen adsorption on Pt/WO_3-ZrO_2 was measured in the adsorption temperature range of 323-573 K and an initial hydrogen pressure of 50 Torr.The rates of hydrogen uptake were very high for the initial few minutes and the adsorption continued for more than 5 h below 523 K.The hydrogen uptake far exceeded the H/Pt ratio of unity for all adsorption temperatures,indicating that the adsorption of hydrogen involved the dissociative adsorption of hydrogen on Pt sites to form hydrogen atoms,the spillover of hydrogen atoms onto the surface of the WO_3-ZrO2 catalyst,the diffusion of spiltover hydrogen atom over the surface of the WO_3-ZrO_2 catalyst,and the formation of protonic acid site originated from hydrogen atom by releasing an electron in which the electron may react with a second hydrogen atom to form a hydride near the Lewis acid site.The rate determining step was the spillover with the activation energy of 12.3 kJ/mol.The rate of hydrogen adsorption cannot be expressed by the rate equation based on the assumption that the rate determining step is the surface diffusion.The activity of Pt/WO_3-ZrO_2 was examined on n-heptane isomerization in which the increase of hydrogen partial pressure provided positive-effect on the conversion of n-heptane and negative-effect on the selectivity towards iso-heptane.     

A study of zinc complexes of the metalloligand [Pt2(μ-S)2(PPh3)4] of the type [Pt2(μ-S)2(PPh3)4ZnL]+ (L = bidentate chelating ligand)

Reactions of [Pt₂(μ-S)₂(PPh₃)₄] with zinc acetate and an ancillary chelating ligand L (HL = 8-hydroxyquinoline, 8-tosylaminoquinoline or maltol) with added trimethylamine in methanol give new cationic platinum–zinc sulfide aggregates [Pt₂(μ-S)₂(PPh₃)₄ZnL]⁺, isolated as their BF₄^? salts. The complexes were characterized by NMR spectroscopy, ESI mass spectrometry, microelemental analysis, and an X-ray structure determination of the tosylamidoquinoline derivative [Pt₂(μ-S)₂(PPh₃)₄Zn(TAQ)]BF₄, which showed a distorted tetrahedral coordination geometry at zinc. Additional examples, containing picolinate, dithiocarbamate, or dithiophosphinate ligands were also synthesized and partly characterized in order to demonstrate a wider range of available derivatives.     

Synthesis and Crystal Structure of Platinum Blue [(1,10-phen)Pt(μ-NHCOCH3)2Pt(1,10-phen)]2(NO3)4

The reaction of acetamide with PtphenCl₂ gave a mixed-valence black-brown-colored platinum complex Ptphen(NHCOCH₃)NO₃ (I), which was studied by X-ray diffraction. The monoclinic crystal (a = 16.389(6) Å, b = 19.664(6) Å, c = 11.049(4) Å; β = 122.8(3)°, V = 2993(18) ų, space group C2/m, Z = 4, R = 0.0432) is built of dimeric [Pt₂phen₂(NHCOCH₃)₂]²⁺ cations and NO ₃ ² . anions. Each platinum atom in the dimer is linked to two nitrogen or oxygen atoms of the two bridging (NHCOCH₃)^? groups and two phenanthroline nitrogen atoms. The Pt-Pt distance in the dimer is 2.8891(19) Å. In the crystal, the dimers form pairs (tetramers), the interdimer Pt…Pt distance being 3.167(2) Å. Four platinum atoms are arranged nearly linearly (the Pt(2)Pt(1)Pt(1)* angle is 178.71(4)°). The UV-Vis spectrum of an aqueous solution of compound I exhibits bands at 360, 480, 630, 680, and 880 nm in the visible region. The diffuse reflectance spectrum of a polycrystalline sample of I (in the 300–900 nm range) contains bands at ～360, ～500, ～600, ～690, and ～890 nm.     

A Kinetic Fluorimetric Method for Determination of Microamounts of Pt(IV) with 2-2′ Dipyridylketone Hydrazone

Abstract

A kinetic method for determination of traces of Pt(IV) based on the aerobic oxidation of the hydrazone of 2-2′ dipyridylketone, in which the formation of a fluorescent product (λ_ex = 359 nm, λ_em = 435 nm) takes place, is described. The reaction is followed by the measurement of the rate of appearance of the fluorescence. The proposed method suffers very few interferences.     

Variance of Solid-state Pt···Pt Interactions in Luminescent Cyclometalated Cationic Pt(Ⅱ)-isocyanide Complexes

Polymorphic structures of cyclometalated cationic Pt(Ⅱ)-isocyanide complexes(–)-1 [Pt((-)-NNC)(Dmpi)]Cl with different packing modes can be isolated before. In this paper, a series of solid-state powders with variable colors(yellow, orange and red) have been obtained from the evaporation of complex(–)-1 in different solvents. The crystallinity, thermogravimetric properties, absorption, luminescence and excited state lifetimes have been studied. In addition, intermolecular Pt···Pt interactions in the optimized configurations of different aggregates have been explored, and calculations of frontier molecular orbitals of monomer, dimer, trimer and tetramer have been carried out.     

Alkylation of [Pt2(μ-S)2(PPh3)4] with boronic acid derivatives

The reactivity of the metalloligand [Pt₂(μ-S)₂(PPh₃)₄] with the boron-functionalized alkylating agents BrCH₂(C₆H₄)B(OR)₂ (R = H or C(CH₃)₂) was investigated by electrospray ionization mass spectrometry (ESI-MS) in real time using pressurized sample infusion (PSI). The macroscopic reaction of [Pt₂(μ-S)₂(PPh₃)₄] with one mole equivalent of alkylating agents BrCH₂(C₆H₄)B{OC(CH₃)₂}₂ and BrCH₂(C₆H₄)B(OH)₂ gave the dinuclear monocationic μ-sulfide thiolate complexes [Pt₂(μ-S){μ-SCH₂(C₆H₄)B{OC(CH₃)₂}₂}(PPh₃)₄]⁺ and [Pt₂(μ-S){μ-S⁺CH₂(C₆H₄)B(OH)(O^?)}(PPh₃)₄]. The products were isolated as the [PF₆]^? salt and zwitterion, respectively, and fully characterized by ESI-MS, IR, ¹H and ³¹P NMR spectroscopy, and single-crystal X-ray structure determinations.     

(η~2C_(60))Pt (PPh_3)_2 as the Catalystfor the Hydrosilylation of Olefins

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Oxidation of coordinated ethylenediamine in platinum(IV) complexes with bromine. Crystal structures of [Pt(en)Py2Br2]Br2 · H2O, [Pt(HN-C(O)-C(O)-NH)Py2Br2] · H2O, and [Pt(en)PyBr3]NO3

Heating of an aqueous solution of [Pt(en)Py₂Cl₂]Cl₂ · 2H₂O (I) with KBr excess leads to the formation of [Pt(en)Py₂Br₂]Br₂ · H₂O (II). The interaction of a solution of II with bromine water results in the precipitation of polybromide ([Pt(en)Py₂Br₂]Br₂ · Br₂), which within a few days in the reaction solution partly transforms into oximide platinum(IV) complex, [Pt(HN-C(O)-C(O)-NH)Py₂Br₂] · H₂O (III). Complex [Pt(en)PyBr₃]Br · H₂O (IV) with an impurity of II was prepared by reacting KBr excess and the product of [Pt(en)Py₂]Cl₂ oxidation with chlorine in 0.05 N HCl. The action of HNO₃ on the solution of IV produced a nitrate derivative ([Pt(en)PyBr₃]NO₃, V). Complex IV, unlike II, does not react with bromine. The IR spectra of all the obtained compounds were recorded. Complexes II, III, and V were studied by X-ray crystallography. The crystals of II are monoclinic, space group P2₁/c, a = 15.640(2) Å, b = 9.345(1) Å, c = 14.167(2) Å, β = 102.63(1)°, V = 2020.5(5) ų, Z = 4, R _hkl = 0.033. The crystals of III are triclinic, space group P $\bar 1$ , a = 7.108(1) Å, b = 10.946(1) Å, c = 11.020(2) Å, α = 83.63(1)°, β = 80.31(1)°, γ = 75.02(1)°, V = 814.4(2) ų, Z = 2, R _hkl = 0.033. In the near-planar five-membered chelate ring (torsion angle NCCN is 7°), the C-O distances (1.23(1) Å) correspond to double bonds; the C-C (1.53(1) Å) and C-N (1.31(1) Å), distances correspond to ordinary bonds. The crystals of V are monoclinic, space group P2₁/c, a = 8.306(2) Å, b = 8.995(2) Å, c = 20.231(4) Å, β = 97.48(2)°, V = 1498.6(6) ų, Z = 4, R _hkl = 0.037.     

Synthesis and properties of ms- and β-substituted Pt(II) and Pt(IV) tetraphenylporphyrinates

The interaction of 5,10,15,20-tetraphenylporphyrin, 5,10,15,20-tetra-(4-chlorophenyl)porphyrin, 2-bromo-5,10,15,20-tetraphenylporphyrin, and 2,3,12,13-tetrabromo-5,10,15,20-tetraphenylporphyrin with platinum(II) chloride in boiling phenol has been studied. The corresponding platinum(II) porphyrinates have been synthesized; their subsequent treatment with bromine in chloroform resulted in platinum(IV) porphyrinates. The Pt(II) and Pt(IV)(Br)₂ porphyrinates have been identified by elemental analysis, electron absorption, IR, and ¹H NMR spectroscopy.     

Chemical and thermal destruction of the platinum blue {Pt(Bipy)(NHCOCH3)2NO3 · mH2O}. The molecular and crystal structures of new binuclear Pt(III) acetamide [Pt2(Bipy)2(NHCOCH3)2(μ-NHCOCH3)2](NO3)2 · H2O

The chemical reactivity of mixed-valence “platinum blue” of the composition [Pt(Bipy)(NHCOCH₃)₂NO₃ · mH₂O] _n (I) towards water, concentrated HCl, and ethanol was studied. The reaction of compound I with water gave previously unknown binuclear Pt(III) acetamide [Pt₂(Bipy)₂(μ-NHCOCH₃)₂(NHCOCH₃)₂](NO₃)₂ · H₂O (II) (yield 19%), which was studied by X-ray diffraction. Upon the reaction of “blue” I with HCl_conc, destruction took place to give PtBipyCl₃ and Pt(IV) oxonium hexachloroplatinate (H₃O)₂[PtCl₆] the structure of which was studied by X-ray diffraction; treatment of I with ethanol leads to partial reduction of the “blue” and destruction giving (according to X-ray diffraction data) the Pt(II) complex [Pt(Bipy)₂](NO₃)₂ · H₂O (III). Thermal decomposition of I under inert atmosphere was studied by DSC and TGA.     

Far infrared spectra of K2Pt(CN)4Br0.3·3.2H2O

Polarized far i.r. reflection spectra of K₂Pt(CN)₄Br_0.3·3.2H₂O were measured at 220, 150 and 80 K for the frequency range 15–400 cm⁻¹. The E|c and E ⊥ c spectra were analysed on the basis of the one- and four-oscillator model, respectively. Observed bands were interpreted based on the average structure (C¹_4υ, Z = 2), not taking into account Peierls distortion.     

Synthesis,characterization and electrocatalytic activity for ethanol oxidation of carbon supported Pt,Pt–Rh,Pt–SnO2 and Pt–Rh–SnO2 nanoclusters

Nanoclusters of Pt, Pt–Rh, Pt–SnO₂ and Pt–Rh–SnO₂ were successfully synthesized by polyol method and deposited on high-area carbon. HRTEM and XRD analysis revealed two phases in the ternary Pt–Rh–SnO₂/C catalyst: solid solution of Rh in Pt and SnO₂. The activity of Pt–Rh–SnO₂/C for ethanol oxidation was found to be much higher than Pt/C and Pt–Rh/C and also superior to Pt–SnO₂/C. Quasi steady-state measurements at various temperatures (30–60 °C), ethanol concentrations (0.01–1 M) and H₂SO₄ concentrations (0.02–0.5 M) showed that Pt–Rh–SnO₂/C is about 20 times more active than Pt/C in the potential range of interest for the fuel cell application.     

Sb在Pt(100),Pt(110),Pt(111)及Pt(320)上不可逆吸附的电化学特性

研究了Sb在Pt(1 0 0 ) ,Pt(1 1 0 ) ,Pt(1 1 1 )和Pt(32 0 )单晶面上不可逆吸附的电化学特性 .发现当扫描电位的上限Eu≤ 0 .45V时 ,Sbad可以稳定地吸附在Pt(1 0 0 ) ,Pt(1 1 0 )和Pt(1 1 1 )表面 ,而Sbad在Pt(32 0 )表面稳定的电位较低 ,为Eu≤ 0 .40V .从饱和吸附Sb的铂单晶电极出发 ,通过改变电位扫描上限Eu 和电位扫描圈数可以获得不同Sb覆盖度 (θSb)的电极 .根据Sb和H在铂单晶电极表面共吸附的定量数据 ,对Sb在不同铂单晶面上饱和吸附的模型进行了初步探讨 .     

Evidence for hydrogen bond network formation in microsolvated clusters of Pt(CN)4(2-): collision induced dissociation studies of Pt(CN)4(2-)·(H2O)(n) n = 1-4, and Pt(CN)4(2-)·(MeCN)(m) m = 1, 2 cluster ions

Low-energy collision induced dissociation has been used to investigate the structure and stability of microsolvated clusters of the prototypical, aprotic multiply charged anion, Pt(CN)(4)(2-), i.e. Pt(CN)(4)(2-)·(H(2)O)(n) n = 1-4, Pt(CN)(4)(2-)·(MeCN)(m) m =1, 2, and Pt(CN)(4)(2-)·(H(2)O)(3)·MeCN. For all of the systems studied, the lowest energy fragmentation pathway was found to correspond to decay of the cluster with loss of the entire solvent ensemble. No sequential solvent evaporation was observed. These observations suggest that the Pt(CN)(4)(2-) solvent clusters studied here form hydrogen-bonded "surface solvated" structures. Electronic structure calculations are presented to support the experimental results. In addition, the detailed fragmentation patterns observed are interpreted with reference to the differential solvation of the ionic fragmentation and electron detachment potential energy surfaces of the core Pt(CN)(4)(2-) dianion. The results described represent some of the first experiments to probe the microsolvation of this important class of multiply charged anions.     

A zwitterionic monoalkylated derivative of [Pt2(μ-S)2(PPh3)4] from 1,3-propanesultone

Reaction of dinuclear platinum(II) sulfido complex [Pt₂(μ-S)₂(PPh₃)₄] with 1,3-propanesultone gives the novel zwitterionic monoalkylated thiolate complex [Pt₂(μ-S){μ-S(CH₂)₃SO₃}·(PPh₃)₄], which was characterized by NMR spectroscopy, electrospray ionisation mass spectrometry, and a single crystal X-ray structure determination. Crystals are monoclinic, space group P2(1)/c with unit cell dimensions a = 16.8957(3) Å, b = 15.5031(3) Å, c = 28.0121(5) Å, β = 99.780(1)°, for Z = 4.     

A theoretical study of an unusual Y-shaped three-coordinate Pt complex: Pt(0) σ-disilane complex or Pt(II) disilyl complex?

The unusual Y-shaped structure of the recently reported three-coordinate Pt complex Pt[NHC(Dip)(2)](SiMe(2)Ph)(2) (NHC = N-heterocyclic carbene; Dip = 2,6-diisopropylphenyl) was considered a snapshot of the reductive elimination of disilane. A density functional theory study indicates that this structure arises from the strong trans influence of the extremely σ-donating carbene and silyl ligands. Though this complex can be understood to be a Pt(II) disilyl complex bearing a distorted geometry due to the Jahn-Teller effect, its (195)Pt NMR chemical shift is considerably different from those of Pt(II) complexes but close to those of typical Pt(0) complexes. Its Si···Si bonding interaction is ~50% of the usual energy of a Si-Si single bond. The interaction between the Pt center and the (SiMe(2)Ph)(2) moiety can be understood in terms of donation and back-donation interactions of the Si-Si σ-bonding and σ*-antibonding molecular orbitals with the Pt center. Thus, we conclude that this is likely a Pt(0) σ-disilane complex and thus a snapshot after a considerable amount of the charge transfer from disilane to the Pt center has occurred. Phenyl anion (Ph(-)) and [R-Ar](-) [R-Ar = 2,6-(2,6-iPr(2)C(6)H(3))(2)C(6)H(3)] as well as the divalent carbon(0) ligand C(NHC)(2) also provide similar unusual Y-shaped structures. Three-coordinate digermyl, diboryl, and silyl-boryl complexes of Pt and a disilyl complex of Pd are theoretically predicted to have similar unusual Y-shaped structures when a strongly donating ligand coordinates to the metal center. In a trigonal-bipyramidal Ir disilyl complex [Ir{NHC(Dip)(2)}(PH(3))(2)(SiMe(3))(2)](+), the equatorial plane has a similar unusual Y-shaped structure. These results suggest that various snapshots can be shown for the reductive eliminations of the Ge-Ge, B-B, and B-Si σ-bonds.