Noble metals in polyoxometalates

Polyoxometalates containing noble metal ions, such as ruthenium, osmium, rhodium, palladium, platinum, silver and gold, are a structurally diverse class of compounds. They include both classical heteropolyanions (vanadates, molybdates, tungstates) in which noble metals are present as heteroatoms, as well as the recently discovered class of polyoxometalates with noble metal "addenda" atoms. The focus of this Review is on complexes that should, in principle, exist as discrete molecular species in solution, and which are therefore of interest for their reactivity, their future synthetic utility and potential applications, for example, in catalysis or nanoscience.     

Surface tension of liquid metals and alloys — Recent developments

Surface tension measurements are a central task in the study of surfaces and interfaces. For liquid metals, they are complicated by the high temperatures and the consequently high reactivity characterising these melts. In particular, oxidation of the liquid surface in combination with evaporation phenomena requires a stringent control of the experimental conditions, and an appropriate theoretical treatment. Recently, much progress has been made on both sides. In addition to improving the conventional sessile drop technique, new containerless methods have been developed for surface tension measurements. This paper reviews the experimental progress made in the last few years, and the theoretical framework required for modelling and understanding the relevant physico-chemical surface phenomena.     

燃烧过程中碱/碱土金属对重金属迁移转化影响的研究进展

碱/碱土金属广泛存在于各种固体燃料中，在燃烧过程中碱/碱土金属与燃料中重金属及其他矿物发生复杂的物理化学反应，从而影响重金属的迁移和转化。本研究主要介绍了碱/碱土金属对As、Se、Pb和Cr四种重金属迁移转化的影响规律，包括碱金属和碱土金属对重金属迁移转化的影响，颗粒物团聚与黏结对重金属排放的影响三个方面。碱/碱土金属能够抑制重金属的挥发：碱金属与Cl元素的结合，降低了PbCl₂的生成；碱金属的存在有利于提升高岭土对Pb的吸附效率；碱/碱土金属可以与As和Se形成稳定的化合物。但同时需要注意碱/碱土金属与Cr的部分结合产物中，Cr以六价态存在，具有较高的毒性。碱/碱土金属对于团聚现象发生，分别起到了促进和抑制作用，适当含量的碱金属有利于减少重金属的释放。通过总结碱/碱土金属对重金属迁移转化的影响规律，以期为降低重金属的危害提供思路。     

The chemistry of carbonyl clusters of transition metals containing labile and hemilabile ligands. Synthesis,reactivity, and prospects for application

The methods of synthesis, structural features, and the reactivity of substituted carbonyl clusters of transition metals containing labile and hemilabile ligands are considered.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2547–2559, December, 2004.     

A perturbed hard-sphere equation of state for liquid metals

A perturbed hard-sphere equation of state, developed previously for liquid alkali metals and liquid refractory metals, has been applied for PVT calculation of some pure liquid metals including alkaline earth metals, tin, lead, antimony, bismuth, and rubidium over a wide range of temperatures and pressures. Two temperature-dependent parameters appear in the equation of state, which are universal functions of the reduced temperature, i.e. two scale parameters are sufficient to calculate the temperature-dependent parameters. The scaling parameters can be easily obtained by employing a corresponding-states principle based on a Lennard-Jones potential energy function. Employing the present equation of state, the liquid densities of aforementioned metals at temperatures ranging from the melting point to 2000?K and at pressures ranging from vapour pressure up to 40,000?bar have been calculated and compared with experimental data. The average absolute deviation in predicted densities compared with experimental data is 1.54%.     

Semi-empirical calculation method for transition metals

A semi-empirical molecular orbital method capable of giving useful bond energy and bond geometry information about transition metal compounds is presented. In this method, which for the first time applies a MINDO procedure to transition metals, the one electron part of the off diagonal Fock matrix elements are put proportional to overlap divided by inter-nuclear distance rather than being proportional to overlap as is conventional. Good results are obtained for FeH, FeH₄, Fe₂, Fe₆, Fe(CO)₅, FeO, O-Fe-O, and FeO₂ (side- and end-bonded).     

Thermal explosion of nitrophenates of transition metals

The thermal decomposition studies on nitrophenates of copper, nickel and cobalt have been undertaken,-t curves show dehydration of these compounds at lower temperatures whereas dehydration cum decomposition seem to occur at higher temperatures leading to oxidative combustion of aromatic part. NO₂ gas is evolved during decomposition which seems to be responsible for oxidative reactions leading to detonation. The explosion temperature and velocity of detonation have been found to be linearly related with the number of nitro groups. The mechanism of thermal explosion has also been discussed.Thanks are due to Prof. S. Giri for providing laboratory facilities; and Aeronautics R&D Board, Ministry of Defence for financial assistance. Authors are also grateful to Shri I. P. S. Kapoor for helpful discussions.     

Frequency spectra of disordered metals: especially liquid Rb

The phonon frequency spectrum g(ω) of a crystal, such as body centred cubic (bcc) Rb, is known to be characterized by the Van Hove singularities at ω?≠?0. However, for a liquid metal like Rb, g(ω) has a single, hydrodynamic-like singularity, namely a cusp ∝ ω ^(1/2), at ω?=?0. Here, we note first that computer simulation on liquid Rb near freezing has revealed a rather well-defined Debye frequency ω_D. Therefore, we propose here a zeroth-order model g ₀ (ω ) of g(ω) for Rb, which combines the Debye model with the ‘hydrodynamic’ ω ^(1/2) cusp. The corresponding velocity autocorrelation function 〈 v (t)·v (0)〉 has correctly a long-time tail ∝ t ^-(3/2). The terms from g ₀ (ω ) involving ω_D are then damped by weak exponential factors exp (-α _i t), and the resulting first-order approximation, g ₁ (ω ) say, to the frequency spectrum is found to have features in common with the molecular dynamics (MD) simulation form. Thus ω_D is fixed, as well as transport coefficients for the known thermodynamic state. The article concludes with a more qualitative discussion on supercooled liquids, and on metallic glasses such as Fe, for which MD simulations exist.     

Monitoring and statistical evaluation of heavy metals in airborne particulates in Cairo, Egypt

Airborne particulate material was monitored as total suspended particles and particulate matter less than 10 μm at selected sites in Cairo. The selected sites represent heavily industrial and industrial–residential areas of Cairo, Egypt. The filters were further analyzed for lead, cadmium, zinc and nickel using ion chromatography. The chosen method was modified to improve resolution and decrease the retention time. The data obtained were treated statistically using one-way analysis of variance and correlated with the anthropological and industrial activities of the sites. The concentrations of the heavy metals are studied in terms of particle size, time dependence, and safety.     

Thermal behaviour of acidic salts of mixed tetravalent metals

The mixed metal phosphates were synthetized by the HF method, the resulting materials being crystalline. Thermal analysis revealed that they contain almost one mole of crystalline water per molecule unit. The mode of thermal decomposition of the samples was similar to those for crystalline phosphates containing only zirconium or titanium.

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Zusammenfassung Die Mischmetallphosphate wurden mit der HF-Methode hergestellt, wobei man kristalline Substanzen erhielt. Die Thermoanalyse zeigte, daß sie fast ein Molekül Kristallwasser pro Moleküleinheit besitzen. Die Art der thermischen Zersetzung der Proben ähnelt der Zersetzung von kristallinen Phosphaten von nur Zirkonium oder nur Titan.

     

The Cadmium Oxide Route to Alkali Metal Oxometallates with Uncommon Structural Features

The aim of this research report is to give an introduction to a specific solid state reaction applied in the field of alkali metal rich transition metal compounds. The approach is an explorative investigation of the oxidation of transition metals with CdO in the presence of alkali metal oxides and / or compounds with complex anions such as Na₂SO₄. Thereby, a range of unusual compounds have been obtained and structurally characterized. In particular, low valences and uncommon coordination numbers (C.N.) of the late 3d transition metals, as well as interesting varieties in the anionic part of the structures are accessible. The presented examples were selected mainly in order of their inherent aspects concerning the reactivity, structural features or electronic structures.     

Metal‐Mediated Functionalization of Natural Peptides and Proteins: Panning for Bioconjugation Gold

Selective modification of natural proteins is a daunting methodological challenge and a stringent test of selectivity and reaction scope. There is a continued need for new reactivity and new selectivity concepts. Transition metals exhibit a wealth of unique reactivity that is orthogonal to biological reactions and processes. As such, metal‐based methods play an increasingly important role in bioconjugation. This Review examines metal‐based methods as well as their reactivity and selectivity for the functionalization of natural proteins and peptides.     

A layered magnetic iron/iron oxide nanoscavenger for the analytical enrichment of ng-L concentration levels of heavy metals from water

Magnetically driven separation techniques have received considerable attention in recent decade because of their great potential application. In this study, we investigate the application of an unmodified layered magnetic Fe/Fe₂O₃ nanoscavenger for the analytical enrichment and determination of sub-parts per billion concentrations of Cd(II), Pb(II), Ni(II), Cr(VI) and As(V) from water samples. The synthesized nanoscavenger was characterized by BET, TGA, XRD and IR and the parameters influencing the extraction and recovery of the preconcentration process were assessed by atomic absorption spectrometry. The possible mechanism of the enrichment of heavy metals on Fe/Fe₂O₃ was proposed, which involved the dominant adsorption and reduction. The nanoscale size offers large surface area and high reactivity of sorption and reduction reactions. The obtained limits of detection for the metals studied were in the range of 20–125 ng L⁻¹ and the applicability of the nanomaterial was verified using a real sample matrix. The method is environmentally friendly as only 15 mg of nanoscavenger are used, no organic solvent is required for the extraction and the experiment is performed without the need for filtration or preparation of packed preconcentration columns.     

Solution extraction of transition and post-transition heavy and precious metals by chelate and macrocyclic ligands

This review focuses on compounds and methods that can be used for the extraction and separation from solution of two classes of elements that we define as heavy metals and precious metals. These elements are often targeted because they are toxic, costly, and their coordination chemistry has already been well studied, and because there is a need to develop methods of economically extracting, separating and recovering them from waste sites. This review outlines possible strategies that can be used, and reviews the present literature regarding the available methods for their extraction.     

Diastereoselective addition of silyl- and stannyl metals to γ-alkoxy-alkylidene malonates

Stereochemical control of the addition of silyl- and stannyl metals to chiral γ-alkoxy-alkylidene malonates proved to be dependant on the nature of the counter ion and of the solvent but in an unpredictable way.     

Investigation of thermal decomposition of anthranilates of alkali metals

The thermal properties of the anthranilates of the alkali metals Li, Na, K, Rb and Cs were studied. Thermal, chemical and X-ray analyses and infrared spectroscopy were used to determine the reactions of decomposition of these compounds. The thermal properties of the anthranilates of the alkali metals were compared with those of other metals.This work was done within Project 01.17: New Methods in Analytical Chemistry and Their Application in the National Economy.     

Catalytic carbophilic activation: catalysis by platinum and gold pi acids

The ability of platinum and gold catalysts to effect powerful atom-economic transformations has led to a marked increase in their utilization. The quite remarkable correlation of their catalytic behavior with the available structural data, coordination chemistry, and organometallic reactivity patterns, including relativistic effects, allows the underlying principles of catalytic carbophilic activation by pi acids to be formulated. The spectrum of reactivity extends beyond their utility as catalytic and benign alternatives to conventional stoichiometric pi acids. The resulting reactivity profile allows this entire field of catalysis to be rationalized, and brings together the apparently disparate electrophilic metal carbene and nonclassical carbocation explanations. The advances in coupling, cycloisomerization, and structural reorganization--from the design of new transformations to the improvement to known reactions--are highlighted in this Review. The application of platinum- and gold-catalyzed transformations in natural product synthesis is also discussed.     

Ion chromatographic determination of alkali and alkaline earth metals in mineral waters

Summary The rapid, simultaneous, suppressed ion chromatographic determination of alkali, alkaline earth metals and ammonium in highly mineralized waters has been examined using the novel cation exchange IonPac CS12 column. General ability for the determination of lithium, sodium, ammounium, potassium, magnesium, calcium and strontium in concentrations from a few g to several mg per liter was studied. The relative standard deviations of retention times of all seven cations were below 0.7% and the relative standard deviations of the measurements of peak areas and peak heights were mostly below 5%. Six natural mineral waters of different types were selected for evaluation of the method. It was not possible to determine lithium in the one run and ammonium usually partially coelutes with sodium precluding quantitative determination. Strontium was undetectable because of the necessary dilutions. All the reltionships between peak areas and concentrations or peak height and concentrations were linear and there was also no evidence of the effect of different matrices on the slope of regression lines.     

Thermal decomposition of organic peroxide with metals using calorimeters

In this study, we evaluated the reactivity of organic peroxides with metals. The effect of the metals on the decomposition of organic peroxides was measured using a differential scanning calorimeter (DSC). Results of DSC measurements showed that some organic peroxides have high reactivity with a gold plated cell. Especially, hydroperoxides were decomposed at lower temperature using the gold plated cell when compared to other type of cells. In order to evaluate the effect of metals on the hydroperoxides, the decomposition characteristics of cumenhydroperoxide (CHP) with metal powders were studied using a C80 calorimeter and the products were analyzed by a gas chromatograph. These results indicated that the radical reaction of CHP was catalyzed by the gold and the autocatalytic reaction of CHP was catalyzed by stainless steel (SUS) and hastelloy c (HC).     

Soft scorpionate coordination at alkali metals

Reported here are the single‐crystal X‐ray structure analyses of bis‐μ‐methanol‐κ⁴O:O‐bis{[hydrotris(3‐phenyl‐2‐sulfanylidene‐2,3‐dihydro‐1H‐1,3‐imidazol‐1‐yl)borato‐κ³H,S,S′](methanol‐κO)sodium(I)}, [Na₂(C₂₇H₂₂BN₆S₃)₂(CH₄O)₄] (NaTm^Ph), bis‐μ‐methanol‐κ⁴O:O‐bis{[hydrotris(3‐isopropyl‐2‐sulfanylidene‐2,3‐dihydro‐1H‐1,3‐imidazol‐1‐yl)borato‐κ³H,S,S′](methanol‐κO)sodium(I)}–diethyl ether–methanol (1/0.3333/0.0833), [Na₂(C₁₈H₂₈BN₆S₃)₂(CH₄O)₄]·0.3333C₄H₁₀O·0.0833CH₃OH (NaTm^iPr), and a novel anhydrous form of sodium hydrotris(methylthioimidazolyl)borate, poly[[μ‐hydrotris(3‐methyl‐2‐sulfanylidene‐2,3‐dihydro‐1H‐1,3‐imidazol‐1‐yl)borato]sodium(I)], [Na(C₁₂H₁₆BN₆S₃)] ([NaTm^Me]_n). NaTm^iPr and NaTm^Ph have similar dimeric molecular structures with κ³H,S,S′‐bonding, but they differ in that NaTm^Ph is crystallographically centrosymmetric (Z′ = 0.5) while NaTm^iPr contains one crystallographically centrosymmetric dimer and one dimer positioned on a general position (Z′ = 1.5). [NaTm^Me]_n is a one‐dimensional coordination polymer that extends along the a direction and which contains a hitherto unseen side‐on η²‐C=S‐to‐Na bond type. An overview of the structural preferences of alkali metal soft scorpionate complexes is presented. This analysis suggests that these thione‐based ligands will continue to be a rich source of interesting alkali metal motifs worthy of isolation and characterization.