Noble Metal Compounds Research Articles

Synergistic Effects of MOFs and Noble Metals in Photocatalytic Reactions: Mechanisms and Applications.

Photocatalytic technology can efficiently convert solar energy to chemical energy and this process is considered as one of the green and sustainable technology for practical implementation. In recent years, metal-organic frameworks (MOFs) have attracted widespread attention due to their unique advantages and have been widely applied in the field of photocatalysis. Among them, noble metals have contributed significant advances to the field as effective catalysts in photocatalytic reactions. Importantly, noble metals can also form a synergistic catalytic effect with MOFs to further improve the efficiency of photocatalytic reactions. However, how to precisely control the synergistic effect between MOFs and noble metals to improve the photocatalytic performance of materials still needs to be further studied. In this review, the synergistic effects of MOFs and noble metal catalysts in photocatalytic reactions are firstly summarized in terms of noble metal nanoparticles, noble metal monoatoms, noble metal compounds, and noble metal complexes, and focus on the mechanisms and advantages of these synergistic effects, so as to provide useful guidance for the further research and application of MOFs and contribute to the development of the field of photocatalysis.

PLATINUM-PALLADIUM OCCURRENCE VASILINOVSKOE: A NEW TYPE OF NOBLE-METAL MINERALIZATION IN THE URALS

For the first time, a new noble-metal (Pt–Au–Pd) Vasilinovskoe ore occurrence discovered near the village of Kharp in the Yamalo-Nenets Autonomous Okrug is described. It is associated with amphibolized gabbroids and subordinate pyroxenites of the Kershor complex, dated mainly to the Late Ordovician. In these rocks, mineralization zones with an apparent thickness from 0.5 to 50 m (sulfides 3–5 vol.%, occasionally more) are developed. In areas with scattered or finely nested sulfide inclusions, feldspar-quartz, epidote and other veins are often present. According to assay data, in substantially sulfide 0.5–1 kg samples of these, in general, low–sulfide zones, the Pd content reaches 1.4 g/t, Au – 0.8 g/t, and Pt – 0.2 g/t. PGE minerals are represented by abundant secretions of micron–sized palladium tellurides – merenskite PdTe2, temagamite Pd3HgTe3, kotulskite PdTe, as well as other noble metal compounds – sadberite PdSb, arsenopalladinite Pd8(As,Sb)3 and others. In addition to these palladium minerals, the magnetite–chalcopyrite–pyrite association contains microinclusions of native silver, native bismuth and native tin. In the later polysulfide–feldspar–carbonate–quartz association, Au and Ag tellurides, native gold (including Hg-bearing), Se-containing argentite, greenockite are found. The formation of parageneses of precious metals is associated with late magmatic processes, as well as with redistribution by subsequent magmatogenic hydrothermal fluids, up to a temperature of ~250°C; pressure decreased from ~0.9–1.3 to ~0.4–0.5 kbar.

Computational Design of a Two-Dimensional Copper Carbide Monolayer as a Highly Efficient Catalyst for Carbon Monoxide Electroreduction to Ethanol.

Rationally designing stable and low-cost electrocatalysts with high efficiency is of great significance for the large-scale electrochemical reduction of carbon monoxide (eCOR) to high-value-added multicarbon products. Inspired by the tunable atomic structures, abundant active sites, and excellent properties of two-dimensional (2D) materials, in this work, we designed several novel 2D C-rich copper carbide materials as eCOR electrocatalysts by performing an extensive structural search and comprehensive first-principles computations. According to the computed phonon spectra, formation energies, and ab initio molecular dynamics simulations, we screened out two highly stable candidates, i.e., CuC2 and CuC5 monolayers with metallic features. Interestingly, the predicted 2D CuC5 monolayer exhibits superior eCOR performance for C2H5OH synthesis with high catalytic activity (low limiting potential of -0.29 V and small activation energy for C-C coupling of 0.35 eV) and high selectivity (significant suppressing effect on the side reactions). Thus, we predicted that the CuC5 monolayer holds great potential as an eligible electrocatalyst for CO conversion to multicarbon products, which could motivate more study to develop highly efficient electrocatalysts in similar binary noble-metal compounds.

Recent progress in noble-metal-free electrocatalysts for alkaline oxygen evolution reaction.

The practical application of splitting water to generate hydrogen is to a large extent hindered by an oxygen evolution reaction (OER) process. Electrocatalysts with low-cost, high activity, and durability are essential for the low kinetic threshold of the OER. Despite the high active performances of noble metal compound electrocatalysts like IrO2 and RuO2, they are heavily restricted by the high cost and scarcity of noble metal elements. In this context, noble-metal-free electrocatalysts have acquired increasing significance in recent years. So far, a broad spectrum of noble-metal-free electrocatalysts has been developed for improved OER performance. In this review, three types of electrolysis and some evaluation criteria are introduced, followed by recent progress in designing and synthesizing noble-metal-free alkaline OER electrocatalysts, with the classification of metal oxides/(oxy)hydroxides, carbon-based materials, and metal/carbon hybrids. Finally, perspectives are also provided on the future development of the alkaline OER on active sites and stability of electrocatalysts.

PROPERTIES OF POLYMERS BASED ON AROMATIC DIAMINES

This review provides detailed information on the synthesis, structure, properties, methods for studying, and areas of application conductive polymers synthesized on the basis of phenylenediamines. Conductive polymers based on phenylenediamines are cationic salts of highly conjugated polymers and are synthesized by electrochemical or chemical oxidation. Chemical oxidative polymerization has led to the formation of various functional polymers. Depending on the reaction conditions, polyphenylenediamines are produced as powders, colloidal dispersions, thin films, or composites. The close similarity of the chemical structure of polyanilines and polyphenylenediamines endows both groups with some similar properties, such as, for example, redox activity. They act as reductants of noble-metal compounds to the corresponding metals. Due to electrical conductivity and redox activity, as well as the dependence of electrical conductivity on the degree of protonation, it is possible to create various sensors based on polyphenylenediamines. In addition, polyphenylenediamines can be used as one of the components of composite materials, for example, in anticorrosion coatings. In general, some main groups of applications for polyphenylenediamines can be distinguished. The literature indicates a number of areas of their application; they include the corrosion protection of metals, catalysis, electrorheology, sensors, energy-conversion devices, electrochromism, noble-metal recovery, and water treatment. At the same time, polymers of phenylenediamines can be used in medicine, unlike aniline and its oligomers, which have potential toxicity

Progress of Nanomaterials-Based Photothermal Therapy for Oral Squamous Cell Carcinoma

Oral squamous cell carcinoma (OSCC) is one of the top 15 most prevalent cancers worldwide. However, the current treatment models for OSCC (e.g., surgery, chemotherapy, radiotherapy, and combination therapy) present several limitations: damage to adjacent healthy tissue, possible recurrence, low efficiency, and severe side effects. In this context, nanomaterial-based photothermal therapy (PTT) has attracted extensive research attention. This paper reviews the latest progress in the application of biological nanomaterials for PTT in OSCC. We divide photothermal nanomaterials into four categories (noble metal nanomaterials, carbon-based nanomaterials, metal compounds, and organic nanomaterials) and introduce each category in detail. We also mention in detail the drug delivery systems for PTT of OSCC and briefly summarize the applications of hydrogels, liposomes, and micelles. Finally, we note the challenges faced by the clinical application of PTT nanomaterials and the possibility of further improvement, providing direction for the future research of PTT in OSCC treatment.

Advances in Electrochemical Detection Electrodes for As(III).

Arsenic is extremely abundant in the Earth’s crust and is one of the most common environmental pollutants in nature. In the natural water environment and surface soil, arsenic exists mainly in the form of trivalent arsenite (As(III)) and pentavalent arsenate (As(V)) ions, and its toxicity can be a serious threat to human health. In order to manage the increasingly serious arsenic pollution in the living environment and maintain a healthy and beautiful ecosystem for human beings, it is urgent to conduct research on an efficient sensing method suitable for the detection of As(III) ions. Electrochemical sensing has the advantages of simple instrumentation, high sensitivity, good selectivity, portability, and the ability to be analyzed on site. This paper reviews various electrode systems developed in recent years based on nanomaterials such as noble metals, bimetals, other metals and their compounds, carbon nano, and biomolecules, with a focus on electrodes modified with noble metal and metal compound nanomaterials, and evaluates their performance for the detection of arsenic. They have great potential for achieving the rapid detection of arsenic due to their excellent sensitivity and strong interference immunity. In addition, this paper discusses the relatively rare application of silicon and its compounds as well as novel polymers in achieving arsenic detection, which provides new ideas for investigating novel nanomaterial sensing. We hope that this review will further advance the research progress of high-performance arsenic sensors based on novel nanomaterials.

Photoactive iron complexes: more sustainable, but still a challenge

With the “Criticality Score” used as a benchmark for sustainability – potentials, strategies and challenges are discussed to replace noble metal compounds in photosensitizers by the sustainable alternative iron.

(Invited) Enhancement of Plasmon-Induced Charge Separation through Plasmon Coupling

Plasmon-induced charge separation (PICS)1,2 involves electron transfer from plasmonic noble metal nanoparticles or compound nanoparticles to an n-type semiconductor such as TiO2. Oxidation reactions involved in PICS are based on a charge accumulation mechanism (Figure a) or a hole ejection mechanism (Figure b).3 The latter enables nanoscale local oxidation at relatively positive potentials.4-7 This can be applied to photoinduced nanofabrication beyond the diffraction limit of light. For instance, chiral plasmonic nanostructures can be prepared by PICS under right or left circularly polarized light (Figure c).8,9 Some other applications of the plasmonic hole ejection will also be mentioned. Enhancement of PICS with hole ejection through plasmon coupling10 and its application to photocatalysis will also be described.References Y. Tian and T. Tatsuma, J. Am. Chem. Soc., 127, 7632 (2005).T. Tatsuma, H. Nishi, and T. Ishida, Chem. Sci., 8, 3325 (2017) [review].T. Tatsuma and H. Nishi, Nanoscale Horiz., 5, 597-606 (2020) [review].E. Kazuma, N. Sakai, and T. Tatsuma, Chem. Commun., 47, 5777 (2011).I. Tanabe and T. Tatsuma, Nano Lett., 12, 5418 (2012).K. Saito, I. Tanabe, and T. Tatsuma, J. Phys. Chem. Lett., 7, 4363 (2016).H. Nishi, M. Sakamoto, and T. Tatsuma, Chem. Commun., 54, 11741 (2018).K. Saito and T. Tatsuma, Nano Lett., 18, 3209 (2018).K. Morisawa, T. Ishida, and T. Tatsuma, ACS Nano, 14, 3603 (2020).T. Ishida and T. Tatsuma, J. Phys. Chem. C, 122, 26153 (2018). Figure 1

Ground- and Excited-State Properties of Iron(II) Complexes Linked to Organic Chromophores.

Two new bichromophoric complexes, [Fe(bim-ant)2]2+ and [Fe(bim-pyr)2]2+ ([H2-bim]2+ = 1,1'-(pyridine-2,6-diyl)bis(3-methyl-1H-imidazol-3-ium); ant = 9-anthracenyl; pyr = 1-pyrenyl), are investigated to explore the possibility of tuning the excited-state behavior in photoactive iron(II) complexes to design substitutes for noble-metal compounds. The ground-state properties of both complexes are characterized thoroughly by electrochemical methods and optical absorption spectroscopy, complemented by time-dependent density functional theory calculations. The excited states are investigated by static and time-resolved luminescence and femtosecond transient absorption spectroscopy. Both complexes exhibit room temperature luminescence, which originates from singlet states dominated by the chromophore (1Chrom). In the cationic pro-ligands and in the iron(II) complexes, the emission is shifted to red by up to 110 nm (5780 cm-1). This offers the possibility of tuning the organic chromophore emission by metal-ion coordination. The fluorescence lifetimes of the complexes are in the nanosecond range, while triplet metal-to-ligand charge-transfer (3MLCT) lifetimes are around 14 ps. An antenna effect as in ruthenium(II) polypyridine complexes connected to an organic chromophore is found in the form of an internal conversion within 3.4 ns from the 1Chrom to the 1MLCT states. Because no singlet oxygen forms from triplet oxygen in the presence of the iron(II) complexes and light, efficient intersystem crossing to the triplet state of the organic chromophore (3Chrom) is not promoted in the iron(II) complexes.

Ru-impregnated needle-like NiCo2O4 embedded in carbon textiles as O2 electrode for a flexible Li–O2 battery

The synergistic effect between noble metal and spinel-type compounds is beneficial for enhancing the electrochemical performance in a Li–O2 battery. Herein, Ru-impregnated needle-like NCO embedded in porous carbon textiles (CTs) (x wt% Ru@NCO/CTs (x = 0, 0.5, 1, 2, and 5)) is applied as a flexible and binder-free O2 electrode for Li–O2 batteries. The NCO structure can benefit to the Li+ migration, O2 diffusion, and Li2O2 accommodation. The Ru nanoparticles can promote OER and ORR reaction kinetics and lower the overpotential. A flexible Li–O2 cell with 1 wt% Ru@NCO/CTs exhibits a good cyclic stability of 360 cycles with an overpotential of 0.78 V at a constant current density of 200 mA/g, a considerable rate performance, a high reversibility with the Li2O2 formation and its reverse decomposition, and a good flexibility stability under bending and twisting at the different conditions. This work can contribute to the development of electrode material and its architecture design for portable and wearable devices.

Восстановление каталитической активности поверхности и стабилизация активирующего раствора на основе меди(I) перед химическим меднением

Methods of chemical activation of the dielectric surface, in which metal-catalyst particles are formed on it as a result of chemical transformations, are more universal, since they allow to vary the compositions of solutions of chemical deposition of metal and to precipitate metals on substrates of different chemical nature with different morphology and surface structure. Noble metal compounds and colloidal solutions characterized by limited storage stability due to the coagulation process are mainly used for surface activation. Palladium-free activation is used for metallization of the surface of unfolded dielectrics and metallization of through holes of printed circuit boards. As a dielectric material used inorganic materials (ceramics, polycore, various types of ceramics) and organic fiberglass with epoxiconazole adhesive layer. The aim of this work is to improve the technology of activation of non-conductive surfaces by true solutions based on copper(I) by optimizing the composition of the activator. It is shown that the drying temperature affects the composition of the activator layer. Activates the layer obtained by drying at 323-373 K, is composed of CuCl2∙2H2O and Cu2O. The optimum mode of drying an activating solution based on copper(I) (T = 353-373 K, τ = 15-20 minutes). The compounds formed during the drying of the activating solution based on copper monochloride do not have catalytic activity sufficient to initiate chemical and electrochemical metallization reactions. Therefore, it is necessary to carry out an additional operation-acceleration in solutions of reducing agents. Solutions of hydrazine chloride (N2H4∙HCl), sodium hypophosphite (NaH2PO4∙H2O), hydroxylammonium chloride (NH2OH∙HCl), the concentration of which varied in the range (0.1-0.5) mol∙l‒1, as well as a solution of alkaline formaldehyde were taken as these solutions. The technology of activator acceleration in a solution of the following composition: hydroxylammonium chloride (NH2OH∙HCl)  0.5 mol∙l-1; pH = 8-10; T = 298 K, which allows to significantly increase the surface concentration of catalytically active centers on the dielectric surface. In order to determine the durability and performance of the activating solution, the stability of the copper (I)  based solution was studied. The durability and performance of the activating solution is ensured by the presence of copper monochloride in it. This is possible if the solution will constantly undergo a reaction of reduction of divalent copper to a monovalent state. For this purpose, sodium hypophosphite in an amount of 0.5 mol∙l‒1 and metallic copper with a concentration of 30 g∙l‒1 were introduced into the activating solution as a reducing agent. The optimal composition of the activating solution containing (mol∙l‒1): copper chloride(I) ‒ 3.10; hydrochloric acid ‒ 3.10; surfactant OP-10  0.01; metallic copper 0.47 was established. Methods of regeneration of copper(I) concentration in activation solutions have been developed, which can significantly extend their service life.

Ultrasonication-Triggered Ubiquitous Assembly of Magnetic Janus Amphiphilic Nanoparticles in Cancer Theranostic Applications.

The ultrasonication-triggered interfacial assembly approach was developed to synthesize magnetic Janus amphiphilic nanoparticles (MJANPs) for cancer theranostic applications, where the biocompatible octadecylamine is used as a molecular linker to mediate the interactions between hydrophobic and hydrophilic nanoparticles across the oil-water interface. The obtained Co cluster-embedded Fe3O4 nanoparticles-graphene oxide (CCIO-GO) MJANPs exhibited superior magnetic heating efficiency and transverse relaxivity, 64 and 4 times higher than that of commercial superparamagnetic iron oxides, respectively. The methodology has been applicable to nanoparticles of various dimensions (5-100 nm), morphologies (sphere, ring, disk, and rod), and composition (metal oxides, noble metal and semiconductor compounds, etc.), thereby greatly enriching the array of MJANPs. In vivo theranostic applications using the tumor-bearing mice model further demonstrated the effectiveness of these MJANPs in high-resolution multimodality imaging and high-efficiency cancer therapeutics. The ubiquitous assembly approach developed in the current study pave the way for on-demand design of high-performance Janus amphiphilic nanoparticles for various clinical diagnoses and therapeutic applications.

Outstanding Water‐Resistance Pd‐Co Nanoparticles Functionalized Mesoporous Carbon Catalyst for CO Catalytic Oxidation at Room Temperature

AbstractCO complete oxidation at room temperature under moisture has the key difficulty in low loading of noble metal compounds. In this paper, a series of Pd−Co functionalized mesoporous carbon‐based (meso‐C) catalysts were masterly designed, and meso‐C support was prepared by the hard template method. Pd−Co/meso‐C catalysts exhibited the high catalytic activity of CO oxidation, the superior Pd−Co/meso‐C catalyst showed excellent water‐resistance, which could maintain 100% conversion beyond 200 h at room temperature. Through a series of characterizations, the superior Pd−Co/meso‐C catalyst possessed higher activity due to smaller cobaltosic oxide (Co3O4) particle size, excellent reducibility, abundant surface active oxygen species, higher tetravalent Pd content, etc. Therefore, it was concluded that the reaction mechanism of CO oxidation on Pd−Co/meso‐C followed the Langmuir‐Hinshelwood + Redox mechanism according to above characterization and activity results. The deactivation of noble metal catalyst was reasonably solved by controlling the dispersion and particle size of Pd−Co.

Conducting polypyrrole nanotubes: a review

Polypyrrole nanotubes rank among the most conducting polymer materials. The role of the templates in the formation of nanotubes is analysed and various models are discussed. Special attention has been paid to the role of methyl-orange dye in guiding one-dimensional morphology. The tuning of reaction conditions by varying temperature, acidity, or the introduction of additives, such as dyes, affects both the morphology and conductivity of polypyrrole. The increase in conductivity need not always be associated with nanotubular morphology. In addition to conductivity, also other physical properties are reviewed with the special attention paid to the characterization by UV–visible, infrared, and Raman spectroscopies. The chemical properties are demonstrated by the ability of polypyrrole to reduce noble-metal compounds, and by salt–base transition associated with the conductivity decrease. Polypyrrole nanotubes maintain the most of conductivity under physiological conditions, and they are still conducting under alkaline conditions in the contrast to globular polypyrrole. Polypyrrole nanotubes convert to nitrogen-containing carbon nanotubes at elevated temperature, thus producing useful carbonaceous materials. To improve the processing, the nanotubes have been used in composites, colloids, or hydrogels. The applications of polypyrrole nanotubes extend to adsorbents, actuators, antioxidants, biomedicine, catalysts and electrocatalysts, electrorheological suspensions, electromagnetic interference shielding, and sensors, especially to those exploiting electrical conductivity and electrochemical activity, such as electrodes in batteries and supercapacitors.

Shaking up gold and palladium

Sometimes, chemistry can be a real grind. But for Tomislav Friscic at McGill University, that’s the whole point. His team has developed a mechanochemical method that turns noble metals like gold and palladium into useful salts and complexes without needing solvents or harsh reagents (Angew. Chem. Int. Ed. 2018, DOI: 10.1002/anie.201712602). Noble metals are widely used in applications, including as catalysts and in electronics, but generating soluble noble metal compounds requires some aggressive conditions. A common way to make their chloride salts, for example, involves reacting the metals with aqua regia, a mixture of concentrated nitric and hydrochloric acids. Friscic’s team came up with a convenient and less hazardous alternative. The chemists mixed metal powder, pellets, or wire with potassium peroxymonosulfate, an oxidizing agent commonly known as Oxone, and simple halide salts such as potassium chloride or ammonium chloride. Then they put the mixture in a zirconia jar with a

K3PO4-catalyzed carbonylation of amines to formamides

Synthesis of formamides from the catalytic carbonylation of amines with CO is of great interest due to their wide applications of formamides as synthetic intermediates and aprotic polar solvents. Up to now, the most commonly used catalysts are either expensive noble metal compounds or difficult-to-handle alkali metal alkoxides. We have found that a solid base, K3PO4 is a highly active and selective catalyst for the carbonylation of primary and cyclic secondary amines, producing corresponding formaldehydes in yields up to 99% at relatively mild conditions. Spectroscopic and quantum mechanical calculation results indicate that such high activity of K3PO4 is closely related to the strong hydrogen bonding ability of PO43− with the amino group of an amine, thereby enhancing the nucleophilicity of the amino group enough to interact with a neutral molecule, CO and mediating proton transfer from the amino group to the carbonyl group. Characterization of spent catalyst by FT-IR and XRD implies that small portion of K3PO4 is converted into less active K2HPO4 during the carbonylation reaction.

Iron-Doped Nickel Cobalt Oxide Based High Performance Oxygen Evolution Reaction Electrode in Alkaline Media

Reducing the overpotentials in the oxygen evolution reaction (OER) in alkaline medium is very important for realizing efficient performance in aqueous metal-air rechargeable batteries and in the electrolysis of water. Noble metal compounds especially based on iridium and ruthenium are good electrocatalysts for OER. Besides these noble-metal-based catalysts, transition metal oxides of the perovskite, spinel and pyrochlore family are also promising electrocatalysts. Since noble metals based catalysts, are not suitable for large-scale application like grid-scale energy storage the research on low-cost OER catalysts based on transition metal oxides is an important area of research. Among various non-noble metal based catalysts, nickel- and cobalt-based mixed oxides, especially the spinel oxide, NiCo2O4, has shown significant activity for OER. [1] The cost of this type of transition metal compounds is significantly lower than that of iridium and ruthenium for a large scale energy storage or electrolysis. [2,3] We present in this talk results on high performance catalysts for oxygen evolution reaction, based on iron-doped NiCo2O4oxides. We have also developed a single-step, low cost, synthetic approach for catalysts and also an electrode. The proposed method is scalable for mass scale production without any major modification. The catalysts are synthesized right on the electrode bypassing separate synthesis of powder catalysts and followed by the construction of the electrode. The direct synthesis of the catalysts on electrode makes the process simple, energy efficient, scalable. The synthesis consists of coating of the precursor solution containing the relevant metals on to a nickel foam electrode of geometric area 25 cm2. This process is now followed by two steps heat treatment to form the final oxide coated electrode. The first step of the heat treatment helps to dry out coating solution on nickel foam. The second step of the heat treatment forms the final catalyst layer. All catalysts sample prepared by this method were investigated using electron microscopy, X-ray diffraction and other material characterization methods. The OER activity was studied in a three electrode cell in 1 M potassium hydroxide solution The steady state polarization method was employed to investigate OER activity. After collection of steady polarization data, electrodes were investigated further for stability. Typically, stability was tested by polarizing the electrode for 100 hours using chrono-potentiometric method at a current density 10 mA/cm2. Figure 1a shows the results of second stage heat treatment temperature on the OER activity, and 1b shows the long term stability test results at a current density 10 mA/cm2. We have found that the overpotential for OER was strongly dependent on second stage heat treatment temperature, and for the best performing catalysts the over potential at 10 mA/cm2current density is ~210mV. The overpotential remained stable over the period of 100 hours. The presentation will discuss these findings more elaborately and offer some insights for the high performance. Acknowledgement The work presented here was funded by the ARPA-E Grids Program, the University of Southern California and the Loker Hydrocarbon Research Institute.

Physical properties of some noble metal compounds from PAW-DFT calculations

The heats of formation, shear modulus, fracture toughness, density and melting points of compounds formed between some noble metals and aluminum, scandium, hafnium and zirconium were evaluated by the ab initio quantum mechanical projector augmented wave (PAW) calculation methods, using the Density Functional Theory (DFT) approach. Out of 24 compounds investigated, 17 are predicted to be thermodynamically feasible. In comparison with Ni3Al, 13 out of the 17 thermodynamically stable compounds are predicted with better hardness. Better fracture toughness and melting points are also predicted in favour of these compounds, suggesting their potentials for engineering applications under extreme conditions. Keywords: Hardness, Poisson’s ratio, bulk modulus, fracture toughness, melting point

Oxoanionic noble metal compounds from fuming nitric acid: the palladium examples Pd(NO3)2 and Pd(CH3SO3)2.

The oxidation of elemental palladium at 100 °C in a mixture of fuming nitric acid and a pyridine-SO3 complex leads to the anhydrous nitrate Pd(NO3)2 (monoclinic, P2(1)/n, Z=2, a=469.12(3) pm, b=593.89(3) pm, c=805.72(4) pm, β=105.989(3)°, V=215.79(2) Å(3)). The Pd(2+) ions are in square-planar coordination with four monodentate nitrate groups which are connected to further palladium atoms, leading to a layer structure. The reaction of elemental palladium with a mixture of fuming nitric acid and methanesulfonic acid at 120 °C leads to single crystals of Pd(CH3SO3)2 (monoclinic, P2(1)/n, Z=2, a=480.44(1) pm, b=1085.53(3) pm, c=739.78(2) pm, β=102.785(1)°, V=376.254(17) Å(3)). Also in this structure the Pd(2+) ions are in square-planar coordination with four monodentate anions; however, the connection to adjacent palladium atoms leads to a chain-type structure. The thermal decomposition of the compounds has been investigated by means of DSC/TG measurements. Furthermore, IR and Raman spectra have been recorded, and an assignment of the observed vibrational frequencies has been carried out based on theoretical investigations.