Thermochemistry of Pd–In,Pd–Sn and Pd–Zn alloy systems

The standard enthalpy of formation of several Pd–M alloys (M = In, Sn and Zn) has been measured using a high temperature direct drop calorimeter. The reliability of the calorimetric results has been determined and supported by using different analytical techniques: light optical microscopy, scanning electron microscopy equipped with electron probe microanalysis (EPMA with EDS detector) and X-ray powder diffraction analysis. The values of Δ_fH (kJ/mol atoms) for the following phases were obtained for the formation in the solid state at 300 K: PdIn (49 at.%In): ?69.0 ± 1.0; Pd₂In₃ ?57.0 ± 1.0; Pd₃In₇: ?43.0 ± 1.0; PdSn₂: ?50.0 ± 1.0; Pd₂Zn₉ (77 at.%Zn): ?33.7 ± 1.0; Pd₂Zn₉ (78 at.%Zn): ?34.0 ± 1.0; Pd₂Zn₉ (80 at.%Zn): ?35.0 ± 1.0. The results show exothermic values which increase from the Pd–Zn to the Pd–Sn and Pd–In systems; the data obtained have been discussed in comparison with those available in literature.     

Synthesis,spectroscopic, luminescent and electrochemical studies of new Ru–Ni–Ru and Pd–Ni–Pd trinuclear complexes with an azolo-linked tetraaza macrocycle

Ru–Ni–Ru and Pd–Ni–Pd trinuclear complexes containing azolo [thiazolo (L¹) and triazolo (L²)] linked 6,8,15,17-tetramethyldibenzo-5,9,14,18-tetraazacyclotetradecene nickel(II) diacetate as a bridging ligand were synthesised and characterized by elemental analysis, conductance and i.r., u.v.–vis., ¹H-n.m.r. spectra and FAB-mass data. The luminescent and electrochemical properties of the complexes were also studied.     

Volatile Pd–Pb and Cu–Pb heterometallic complexes: structure,properties, and trans-to-cis isomerization under cocrystallization of Pd and Cu β-diketonates with Pb hexafluoroacetylacetonate

Preparation of volatile heterometallic precursors is a significant step on the way to advanced multicomponent materials. Study of molecular transformations in solution upon precursor synthesis is of importance to optimize the preparation of the stable solid product of desired composition. Two new volatile heterobimetallic complexes, cis-PdL₂*Pb(hfa)₂ and cis-CuL₂*Pb(hfa)₂, were obtained (L = 2-methoxy-2,6,6-trimethylheptane-3,5-dionate, hfa = 1,1,1,5,5,5-hexafluoropentane-2,4-dionate) under cocrystallization of trans-bis-beta-diketonates of Pd(II) and Cu(II) with Pb(hfa)₂ from organic solvents. Crystals of these compounds are built of discrete bimetallic molecules where transition metal complex isomerized from trans-to-cis form. Complexation followed by isomerization was studied by solution NMR. The bimetallic molecular species were formed early in solution. Enthalpy and activation energy of isomerization were estimated to be 49 and 93 kJ mol^?1, respectively. A new synthesis technique of Pd(II) beta-diketonates which is distinguished by simplicity and selectivity as well as the crystal structure of trans-PdL₂ is described. Volatility of all obtained compounds was confirmed by thermogravimetric analysis and fractional sublimation in vacuum; Pd-containing heterobimetallic complex appeared to be more volatile than both the initial monometallic complexes and Cu-containing complex.     

Heterobimetallic Re–Pd,Re–Au and Re–Cu complexes derived from diphenylphosphino cyrhetrene: Synthesis and X-ray structure

Diphenylphosphinecyrhetrene ligand (η⁵-C₅H₄PPh₂)Re(CO)₃ (1) reacts with 1 equiv. of PdCl₂(NCPh)₂ to form, after workup, the square-planar trans-[(η⁵-C₅H₄PPh₂)Re(CO)₃]PdCl₂(NCMe) (2). Similarly, reaction of 1 with (tetrahydrothiophene)AuCl produces, in excellent yield, the bimetallic complex [(η⁵-C₅H₄PPh₂)Re(CO)₃]AuCl (3) with a linear P–Au–Cl moiety. From the reaction of 2 equiv. of 1 with CuBr(SMe₂) the planar-trigonal complex [(η⁵-C₅H₄PPh₂)Re(CO)₃]₂CuBr (4) was obtained. ³¹P NMR and X-ray crystallography demonstrate, for the three cases, that (η⁵-C₅H₄PPh₂)Re(CO)₃ acts as a monodentate ligand. The structural parameters of the bimetallic complexes are compared with related diphenylphosphinoferrocene metal complexes, described in the literature.     

Low-temperature sol–gel synthesis of anatase nanoparticles modified by Au, Pd and Pt and activity of TiO2/Au, Pd, Pt photocatalysts in water splitting

Base catalyzed hydrolysis and condensation of Ti isopropoxide with water at ambient temperature and molar ratio H₂O/Ti(i-PrOH)₄ varied from 1 to 100 was studied. It was found that molar ratio H₂O/Ti(i-PrOH)₄ = 100 originated amorphous TiO₂-precursor of summary composition TiO_1.9(OH)_0.2 with a specific surface area of 354 m²/g. Low-temperature crystallization of amorphous TiO₂-precursor to nanostructured anatase at 80 °C in a slightly reducing environment of d-glucose was studied. It was found that the low-temperature nucleation and crystallization of anatase was initiated (activated) by combined effects of d-glucose and Au⁰, Pd⁰ and Pt⁰ nanoparticles, generated in situ by slow reduction of Au³⁺, Pd²⁺ and Pt⁴⁺ ions using d-glucose. Considerable photocatalytic activity of Ti-hydroxide-oxide/Au, Pd, Pt catalysts prepared at low-temperature was associated with high content of nanostructured anatase and low content of Au, Pd and Pt nanoparticles (0.02 wt.%) effectively deposited on the surface of titania particles. The maximum hydrogen evolution rates 3.4 μmol/min g at Ti-hydroxide-oxide/Au, 4.0 μmol/min g at Ti-hydroxide-oxide/Pd and 4.1 μmol/min g at Ti-hydroxide-oxide/Pt were found. The activity of all TiO₂/Au, Pd and Pt catalysts increased by calcination at 600 °C from 50 to 100 %.     

Catalytic conversion of cellulose into polyols using carbon-nanotube-supported monometallic Pd and bimetallic Pd–Fe catalysts

A series of carbon nanotube (CNT)-supported monometallic Pd and bimetallic Pd–Fe catalysts were synthesized and employed for catalytic hydrogenolysis of cellulose into polyols, including hexitol, ethylene glycol (EG), 1,2-propanediol (1,2-PG), and glycerol (Gly). The physicochemical properties of the catalysts were characterized by nitrogen physical adsorption measurements, X-ray diffraction analysis, transmission electron microscopy, and X-ray photoelectron spectroscopy. The total yield of hexitol, EG, 1,2-PG, and Gly in hydrolytic hydrogenation of cellulose was 37, 55, and 53% for Pd/CNTs, Pd–Fe/CNTs (Pd:Fe = 1:1), and Pd–Fe/CNTs (Pd:Fe = 1:2), respectively. Addition of Fe to Pd significantly modified the physicochemical properties of the nanoparticles and their catalytic performance, especially regarding hexitol selectivity. The promoting effect of Fe, especially for hexitol selectivity, compared with the monometallic catalyst is due to the fact that incorporation of Fe may stabilize Pd⁰ nanoparticles and lead to downshift of the d-band center of Pd metal nanoparticles by charge transfer from Fe to Pd. Recycling experimental results showed that leaching of Fe resulted in a significant decrease in the hexitol yield obtained using the Pd–Fe/CNTs after the first recycle, further demonstrating that Fe element plays a promoting role for hexitol formation.     

Pd salen complex@CPGO as a convenient,effective heterogeneous catalyst for Suzuki–Miyaura and Heck–Mizoroki cross-coupling reactions

Research on Chemical Intermediates - A Pd(II) Schiff base complex supported on graphene oxide nanosheets (Pd(II) salen@CPGO) has been synthesized and characterized by FT-IR, ICP-AES, XRD, SEM/EDX...     

Phosphine σ-sydnonyl complexes of Ni,Pd, and Pt

3-R"-4-Bromosydnones 1 (R" = Me) and 2 (R" = Ph) react with complexes Ì(PR₃)_n (M = Ni, Pd, Pt) to form mononuclear phosphine -sydnonyl d⁸-complexes of trans-configuration MBr(3-R"-sydnon-4-yl)(PR₃)₂: 3, 4 (Ì = Ni, R" = Ph); 5 (M = Pd, R" = Me); 6a (M = Pd, R" = Ph); 7 (M = Pt, R" = Ph). In the reaction of bromosydnone 2 with Pd(PPh₃)₄, the cis-complex PdBr(3-Ph-sydnon-4-yl)(PPh₃)₂ (6b) is formed initially; 6b rearranges in solution to give trans-complex 6a. On heating in THF, complex 6a is converted into the binuclear [PdBr(3-phenylsydnon-4-yl)(PPh₃)]₂ complex (8). The reaction of 4-chloromercurio-3-phenylsydnone (10) with Ni(PEt₃)₄, Pd(PPh₃)₄, and Pt(PPh₃)₄ gives mononuclear NiCl(3-phenylsydnon-4-yl)(PEt₃)₂ complex (11), binuclear [PdCl(3-phenylsydnon-4-yl) (PPh₃)]₂ complex (14), and cis- and trans-bimetallic PtCl(3-phenylsydnon-4-ylmercurio)(PPh₃)₂ complexes 15a and 15b, respectively. UV irradiation of 15a and 15b in a benzene solution induces redox demercuration to yield the PtCl(3-phenylsydnon-4-ylcarbonyl)(PPh₃)₂ complex (16). In carbonylation of complexes 3, 6, and 7, CO insertion into the M--C bond occurred to form the corresponding acyl derivatives MBr(3-phenylsydnon-4-ylcarbonyl)(PR₃)₂ (17--19).     

Some recent advances in transition-metal-catalyzed ortho SP~2 C–H functionalization using Ru,Rh, and Pd

In the past decade,transition-metal-catalyzed C–H functionalization by weak coordination has emerged as a practical and powerful tool to access many valuable chemicals.Two classes of weakly coordinating directing groups,commonly occurring functional groups,and easily removable auxiliaries,have been found to be efficient and practical for C–H activation reactions.This mini-review contains examples of recent research advances on transition-metal-catalyzed SP2 C–H functionalization via weak coordination,using Ru,Rh,and Pd.A number of weakly coordinating functional groups(e.g.,ketone,ester,carbamate,tertiary amide,ether,thioether,alcohol,and some others)are covered.As the field of transition-metal-catalyzed C–H functionalization continues to develop and more synthetically useful chemo-,regio-,and enantioselective reactions catalyzed by transition metal via weak coordination are discovered,this promising and attractive strategy will play a more important role in modern organic synthesis.     

Preparation of onion-like Pd–Bi–Au/C trimetallic catalyst and their application

This paper describes the preparation of dispersed onion-like Pd–Bi–Au/C catalyst with average diameter of 13 nm obtained by consecutive chemical reduction of precursor gold, bismuth and palladium salts in aqueous solution and immobilization on active carbon. High-resolution transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Auger electron spectroscopy experiments were performed to analyze the structure and to characterize the Pd–Bi–Au/C catalyst. The onion-like morphology is composed of high content of gold inner core, a Bi-rich intermediate layer and a Pd-rich external layer. The catalytic activity of the catalyst was subsequently investigated and they were found to be efficient catalysts for the aerobic liquid phase oxidation. The results showed that the catalytic activity of Pd–Bi–Au/C was higher than that of Pd–Au/C bimetallic catalyst, indicating that bismuth plays an important role in synergistic effect between gold and palladium.     

Complexes of Cu(I) and Pd(II) with (+)-camphor and (–)-cavrone thiosemicarbazones: Synthesis,structure, and cytotoxicity of the Pd(II) complex

CuLCl, CuL¹Cl, PdLCl₂, and PdL¹Cl₂ complexes [L and L¹ being (+)-camphor and (–)-carvone thiosemicarbazones, respectively] have been synthesized. The structure of binuclear [Pd₂L²²Cl₄] complex has been determined by means of X-ray diffraction. The L² ligand (dehydrogenated (–)-carvone thiosemicarbazone) is coordinated via the bridging S atom to two Pd atoms. The complexes of Cu(I) and Pd(II) presumably have polynuclear and binuclear structure, respectively. These facts are in good agreement with IR and NMR spectroscopy as well as mass spectrometry data which indicate the coordination of L and L¹ ligands via the S atom. The influence of L¹ and PdL¹Cl₂ on viability of the Hep2 cell line has been studied. The PdL¹Cl₂ complex is more cytotoxic than L¹ ligand.     

Preparation of polymeric modifier-attached graphene-supported bimetallic Pt–Pd nanocomposites,and their electrochemical properties as electro-catalysts

Graphene-supported bimetallic nanocomposites were synthesized by a modified sodium borohydride reduction method. Poly(diallyldimethylammonium chloride) (PDDA) was used as modifier for good dispersion and higher metal alloy content. The micro-structure and dispersive properties of the electro-catalysts were determined by X-ray diffraction, Fourier-transform-infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. The electrochemical properties of the Pt–Pd electro-catalysts were studied by cyclic voltammetry. This analysis confirmed that functional groups on the graphene oxide (GO) sheet were chemically bonded to the PDDA layer. The average particle diameter of Pt–Pd_{1 to 0.5}–PDDA–reduced graphene oxide (RGO) was found to be 2.4 ± 0.4 nm which is the smallest platinum metal particle size among Pt–Pd–PDDA–RGO electro-catalysts. The electrochemically active surface area was studied and the activity was found to be enhanced by use of the polymeric modifier.     

Calorimetric investigation of order–disorder transition in Cu0.6Pd0.4 and Cu0.85Pd0.15 alloys

Order–disorder phase transitions in Cu_0.6Pd_0.4 and Cu_0.85Pd_0.15 alloys have been investigated using differential scanning calorimetry and drop calorimetry. The differential scanning calorimetry measurements show that the transition in both these alloys are reversible in nature and the enthalpy increment measurements reveal that these transitions are first order in nature. The transition temperature of first-order phase transition in Cu_0.6Pd_0.4 and Cu_0.85Pd_0.15 alloys have been evaluated to be 884(±2) and 799(±2) K, respectively, from drop calorimetric measurements. The latent heat of first-order phase transition in Cu_0.6Pd_0.4 alloy were evaluated to be 31.2(±0.6) and 28.9(±0.5) J g^?1, by enthalpy increment and differential scanning calorimetry measurements, respectively. Similarly, the latent heat of first-order phase transition in Cu_0.85Pd_0.15 alloy were evaluated to be 23.1(±0.6) and 21.3(±0.5) J g^?1, by enthalpy increment and differential scanning calorimetry measurements, respectively. The solidus temperatures of Cu_0.6Pd_0.4 and Cu_0.85Pd_0.15 alloys were found to be 1,457(±2) and 1,360 K, respectively.     

Functionalized cellulose-preyssler heteropolyacid bio-composite: An engineered and green matrix for selective,fast and in–situ preparation of Pd nanostructures: synthesis,characterization and application

A new and green engineered biocomposite was synthesized by sol–gel method, using different loadings of the Preyssler heterpolyacid (8, 15, 25, 40 and 50 wt%) on the functionalized microcrystaline cellulose surface. For the first time, this two-component polymeric biocomposite used for in-situ catalytic synthesis of Pd nanoparticles with the aim of producing tricomponent nanobiocomposites. Preyssler loading on the functionalized surface, controled the size and shape of Pd nanoparticles, time, and pH of their formation. All biocomposites and nanobiocomposites were characterised by FTIR, XRD, BET, TGA, SEM, EDS and TEM. The SEM analysis for two component polymeric biocomposites confirmed the presence of the Preyssler on the surface of functionalized cellulose. The formation of Pd nanoparticles on the surface, was observed by color changing (yellow to deep brown) and confirmed by UV–visible spectroscopy. The Pd nanoparticles formation was fast (2–4 min) for 8 wt% in pH = 2–3 at 80 °C. TEM analysis illustrated the spherical Pd nanoparticles with a size of 5–20 nm, at the lowest loading of Preyssler, and rod shapes with a size of 30–40 nm at the highest loading. The obtained nanobiocomposite exhibited high catalytic activity for the decolourisation of tartrazine, as a model of dyes pollutant in the industry with high degradation efficiency. The catalytic reactions were extended with other azo dyes including methyl orange and rodamine B.     

Application of CE–ICP–MS and CE–ESI–MS in metalloproteomics: challenges,developments, and limitations

Application of capillary electrophoresis (CE) as a high-resolution separation technique in metalloproteomics research is critically reviewed. The focus is on the requirements and challenges involved in coupling CE to sensitive element and molecule-specific detection techniques such as inductively coupled plasma mass spectrometry (ICP–MS) or electrospray ionisation mass spectrometry (ESI–MS). The complementary application of both detection techniques to the structural and functional characterisation of metal-binding proteins and their structural metal-binding moieties is emphasised. Beneficial aspects and limitations of mass spectrometry hyphenated to CE are discussed, on the basis of the literature published in this field over the last decade. Recent metalloproteomics applications of CE are reviewed to demonstrate its potential and limitations in modern biochemical speciation analysis and to indicate future directions of this technique.     

Synthesis of L10 Fe–Pd films by electrodeposition and thermal annealing

Fe–Pd alloy films have been prepared by electrochemical deposition from an alkaline electrolyte containing Fe sulfate, Pd chloride and 5-sulfosalicylic acid onto polycrystalline titanium substrates. The as-deposited films were nanocrystalline and magnetically soft (coercivity ∼ 25 Oe). L1₀ Fe–Pd films with a (1 1 1) preferred orientation were obtained by post-deposition thermal annealing of films with composition about 37 at% Fe in an (Ar + 5% H₂) gas flow at 500 °C. Such films exhibit hard magnetic properties, with a coercivity up to 1880 Oe, and a slightly anisotropic magnetic response, with a larger in-plane remanence. Preliminary magnetic investigations support magnetization switching through pinning of domain walls.     

Thin Pd–23%Ag/stainless steel composite membranes: Long-term stability,life-time estimation and post-process characterisation

The long-term stability of Pd–23%Ag/stainless steel composite membranes has been examined in H₂/N₂ mixtures as a function of both temperature and feed pressure. During continuous operation, the membrane shows a good stability at 400 °C while the N₂ leakage increases very slowly at a temperature of 450 °C (P_feed = 10 bar). After 100 days of operation (P_feed = 5–20 bar, T = 350–450 °C), the N₂ permeance equals 7.0 × 10⁻⁹ mol m⁻² s⁻¹ Pa⁻¹, which indicates that the H₂/N₂ permselectivity still lies around 500, based on a H₂ permeance equal to 3.0 × 10⁻⁶ mol m⁻² s⁻¹ Pa⁻¹. Despite the generation of small pinholes, a membrane life-time of several (2–3) years (T ≤ 425 °C) is estimated for the experimental conditions employed based on long-term stability tests over 100 days. Post-process characterisation shows a considerable grain growth and micro-strain relaxation in the Pd–23%Ag membrane after the prolonged permeation experiment. Changes in surface area are relatively small. In addition, segregation of Ag to the membrane surfaces is observed. The formation of pinholes is identified as the main source for the increased N₂ leakage during testing at higher temperature.     

Bulk properties and hydration numbers of components of water–salt,water–urea,and water–urea–salt systems

With an increase in the concentration of additives, the hydration numbers of compounds decrease. Thus, in a saturated 54.6% solution, urea loses approximately 3/4 of the initial amount of water, forming an aquacomplex of the composition (NH₂)₂CO?H₂O. In a supersaturated 44% solution, the sodium chloride aquacomplex is dehydrated by 2/3, and in a supersaturated 67% solution, sodium sulfate is dehydrated by 5/6. The density of these solutions is 1.354÷1.360 g/cm³ (44% NaCl) and 1.800÷1.849 g/cm³ (67% Na₂SO₄). In a saturated urea solution, NaNO₃, NaCl, and Na₂SO₄ complexes lose 53÷55% of hydration water. It is shown that the interactions in the binary water–urea system somewhat increase the hydration number of the salts (structural hydration). The hydration water density, a structurally important characteristic, increases in the series of solutions of urea, NaNO₃, NaCl, and Na₂SO₄. In the same series of additives, the excess volume of binary water–urea and water–salt systems becomes more negative.     

Thin films of Pd and Pd–1% MWCNT as new electrocatalysts for oxidation of phenol in acid medium

Thin films of pure Pd and composite of Pd and 1% multiwalled carbon nanotube have been obtained on glassy carbon electrodes by borohydride reduction method and investigated as electrocatalysts for the oxidation of phenol in acid medium at 25 °C, using cyclic voltammetry (CV), chronopotentiometry, and high-performance liquid chromatography. The CV study showed that both the electrocatalysts are quite stable and active for the phenol oxidation in acid medium. Further, these electrodes do not seem to undergo deactivation due to intermediates and products formed during the phenol oxidation. With the increase in phenol concentration from 2 to 25 mM, the peak current (I _p) increases initially, reaches maximum at about 15 mM, and tends to decrease thereafter. The peak potential (E _p) value was found to be practically unchanged with phenol concentration. The rate for phenol oxidation (I _p) at the surface of both the electrocatalysts increased with the decrease in pH of the reaction mixture. The electrocatalytic activity of the composite electrode was, however, higher than that of pure Pd under similar experimental conditions. Benzoquinone and hydroquinone were identified as the major phenol degradation intermediate products.