Bonding and redox properties of [Os(3)(CO)(9)(tmbp)(L)] (tmbp=4,4',5,5'-tetramethyl-2,2'-biphosphinine; L=CO, PPh(3)) clusters with an unprecedented electron-deficient metallic core and doubly bridging biphosphinine dianion

Herein we describe in detail the bonding properties and electrochemical behavior of the first known triosmium carbonyl clusters with a coordinated redox-active ligand 4,4',5,5'-tetramethyl-2,2'-biphosphinine (tmbp), the phosphorus derivative of 2,2'-bipyridine. The clusters investigated were [Os(3)(CO)(10)(tmbp)] (1) and its derivative [Os(3)(CO)(9)(PPh(3))(tmbp)] (2). The crystal structures of both clusters are compared with those of relevant compounds; they served as the basis for density functional theory (DFT and time-dependent DFT) calculations. The experimental and theoretical data reveal an unexpected and unprecedented bridging coordination mode of tmbp, with each P atom bridging two metal atoms. The tmbp ligand is formally reduced by transfer of two electrons from the triangular cluster core that consequently lacks one of the metal-metal bonds. Both 1 and 2 therefore represent 50e(-) clusters with a coordinated 8e(-) donor, [tmbp](2-). The HOMO and LUMO of 1 and 2 possess a predominant contribution from different pi*(tmbp) orbitals, implying that the lowest energy excited state possesses a significant intraligand character. This is in agreement with the photostability of these clusters. DFT calculations also predict the experimentally observed structure of 1 to be the most stable one in a series of several plausible structural isomers. Stepwise two-electron electrochemical reduction of 1 and 2 results in dissociation of CO and PPh(3), respectively, and formation of the [Os(3)(CO)(9)(tmbp)](2-) ion. The initially produced radical anions of the parent clusters, in which the odd electron is predominantly localized on the tmbp ligand, are sufficiently stable at low temperatures and can be observed with IR spectroelectrochemistry. The electron-deficiency of the cluster core in 1 permits facile electrocatalytic substitution of a CO ligand by tertiary phosphane and phosphite donors.     

Preparation and characterization of silicate gel glasses containing Cr2O3

The effect of thermal treatment on the structural incorporation of Cr₂O₃ in xCr₂O₃·(100 – x)SiO₂ and 5R _n O·xCr₂O₃·(95 – x)SiO₂ (where x=0.01–1 mol.% and R=Li, Na and Ca) gel glasses was studied by optical absorption spectrophotometry, DTA-TG, XRD and electron microscopy.Samples heat treated at 60°C have green color due to the presence of Cr³⁺ in octahedral coordination. The optical transmission, and color (yellow, orange or ambar), of the samples heat treated between 200 and 700°C prove that Cr³⁺ (octahedrally coordinated) and Cr⁶⁺ (tetrahedrally coordinated) are both present. Segregation of Cr₂O₃ take place at temperatures above 800°C.In reducing conditions the gel glasses were green due to the presence of a high content of Cr³⁺ ions. Samples containing Li or Na show crystalline phases at temperatures below 850°C.     

Reduction of soluble colloidal MnO<Subscript>2</Subscript> by <Emphasis Type="SmallCaps">DL</Emphasis>-malic acid in the absence and presence of nonionic TritonX-100

Kinetics of oxidation of DL-malic acid by water soluble colloidal MnO₂ (prepared from potassium permanganate and sodium thiosulfate solutions) have been studied spectrophotometrically in the absence and presence of nonionic Triton X-100 surfactant. The reaction is autocatalytic and manganese(II) (reduction product of the colloidal MnO₂) may be the autocatalyst. The order of the reaction is first in colloidal [MnO₂] as well as in [malic acid] both in the absence and presence of the surfactant. The reaction has acid-dependent and acid-independent paths and, in the former case, the order is fractional in [H⁺]. The effect of externally added manganese(II) is complex. The results show that the rate constant increases as the manganese(II) concentration is increased. It is not possible to predict the exact dependence of the rate constants on manganese(II) concentration, which has a series of reactions with other reactants. In the presence of TX-100, the observed effect on k is catalytic up to a certain [TX-100]; thereafter, an inhibitory effect follows. The catalytic effect is explained in terms of the mathematical model proposed by Tuncay et al. (in Colloids Surf A Physicochem Eng Aspects 149:279 3). Activation parameters associated with the observed rate constants (k_obs/k) have also been evaluated and discussed.     

Enhancing effect of DNA on chemiluminescence from the decomposition of hydrogen peroxide catalyzed by copper(II)

In the absence of any special luminescence reagent, emission of weak chemiluminescence has been observed during the decomposition of hydrogen peroxide catalyzed by copper(II) in basic aqueous solution. The intensity of the chemiluminescence was greatly enhanced by addition of DNA and was strongly dependent on DNA concentration. Based on these phenomena, a flow-injection chemiluminescence method was established for determination of DNA. The chemiluminescence intensity was linear with DNA concentration in the range 2×10^–7–1×10^–5 g L^–1 and the detection limit was 4.1×10^–8 g L^–1 (S/N=3). The relative standard deviation was less than 3.0% for 4×10^–7 g L^–1 DNA (n=11). The proposed method was satisfactorily applied for determination of DNA in synthetic samples. The possible mechanism of the CL reaction is discussed.     

The Degree of Disorder in Hardwood Kraft Pulps Studied by Means of LODP

The amount of disordered material in two types of hardwood kraft pulps was estimated by determining the weight loss at the point where the levelling-off degree of polymerisation (LODP) was reached. The pulps used were commercial pulps viz (1)one conventional birch kraft and (2)one mixed hardwood (MHW) kraft pulp that had been prehydrolysed prior to cooking. The results indicated that the hemicellulose xylan is closely associated with the cellulose in commercial birch pulps. It is therefore only possible to use LODP as a measure of the crystallite length of hardwood cellulose in highly purified pulps, such as prehydrolysed kraft pulp. A model explaining the LODP-results is proposed.     

A combination atmospheric pressure LC/MS:GC/MS ion source: Advantages of dual AP-LC/MS:GC/MS instrumentation

Modification of commercial LC/MS instrumentation to allow both atmospheric pressure (AP) LC/MS and GC/MS is described. Advantages of this additional capability versus LC/MS alone include higher chromatographic resolution in the GC versus LC mode, greater peak capacity for complex mixture analysis, higher sensitivity for a variety of volatile compounds, and the ability to observe compounds of low polarity that are not readily observed in LC/MS. Advantages over conventional GC/MS include the ability to use higher carrier gas flow and shorter columns for passing less volatile materials through the gas chromatograph, selective ionization, and rapid switching between positive and negative ion modes. Other advantages include application of the enhanced capabilities of LC/MS instrumentation to GC/MS analyses such as cone voltage fragmentation, MS(n), high mass resolution, and accurate mass measurement. Limitations of APGC/MS include the inability to observe saturated hydrocarbon and certain other highly nonpolar compounds and less odd-electron fragmentation for computer aided library searching. For some analyses, the limitation related to ionization of highly nonpolar compounds is advantageous, as is the simplified mass spectrum and easy molecular weight identification that results from less fragmentation observed in the AP ionization mode.     

Diamond paste-based electrodes for determination of Cr(III) in pharmaceutical compounds

A new class of monocrystalline diamond paste-based electrodes is proposed for the determination of chromium(III) at trace levels in vitamins. Three types of monocrystalline diamond—natural diamond 1 (natural diamond), synthetic diamond 50 (synthetic-1), and synthetic diamond 1 (synthetic-2)—were used for electrode construction. The linear concentration ranges are between 10^–10 and 10^–8; 10^–9 and 10^–7, and 10^–10 to 10^–8 mol L^–1, with limits of detection of 10^–12, 10^–12, and 10^–11 mol L^–1, when natural diamond, synthetic-1, and synthetic-2, respectively, are used as electrode materials. For electrodes based on natural diamond and synthetic-1 it was found that Cr(III) yields a peak at about +0.275±0.015 V (vs. Ag/AgCl) within a predetermined positive potential range situated between +0.4 and +0.2 V, while for the electrode based on synthetic-2 the peaks are found at +0.300±0.015 V (vs. Ag/AgCl). The proposed method is reliable for the determination of chromium(III) at trace levels in two vitamin tablets (RSD<0.2%).     

Ferrocenyltrithiocarbonates : I. Direct access from α-ferrocenylcarbinols by a SNi mechanism. Absolute x-ray structure determination of (R)-ferrocenylmethylmethane S-methyl-trithiocarbonate

¹⁰³Rh Chemical shifts of a variety of mono- and di-nuclear rhodium carbonyl complexes are reported together with the modifications to the probe and decoupler unit of a JEOL PS-100 PFT spectrometer which enable these ¹⁰³Rh-decoupled ¹³C NMR measurements to be made. These data are discussed in conjunction with ¹³C NMR data on other rhodium carbonyls.     

Synthesis and applications of poly(acryl<Emphasis Type="Italic">p</Emphasis>-aminobenzenesulfonamideamidine-<Emphasis Type="Italic">p</Emphasis>-aminobenzenesulfonylamide) chelating fiber for pre-concentrating and separating trace Bi(III), Hg(III), Au(III) and Pd(IV) from solution samples

Poly(acrylp-aminobenzenesulfonamideamidine-p-aminobenzenesulfonylamide) chelating fiber containing "S", "N", and "O" elements was synthesized from polyacrylonitrile fiber and p-aminobenzene sulfonamide and used to enrich and separate trace Bi(III), Hg(III), Au(III), and Pd(IV) ions from wastewater and ore sample solution. The enrichment acidity, flow rate, elution conditions, reuse, interference ions, saturated adsorption capacity, constant of adsorption rate, analytical accuracy, and actual samples on chelating fiber were investigated by means of inductively coupled plasma optical emission spectrometry (ICP-OES) with satisfactory results. Solutions of 100 ng mL^–1 of Bi(III), Hg(III), Au(III), and Pd(IV) ions can be enriched quantitatively by this chelating fiber at a rate of 1.0 mL min^–1 at pH 4 and desorbed quantitatively with 20 mL of 0.25 M HCl and 2% CS(NH₂)₂ solution at 50 °C (with recovery 97%). When the chelating fiber was reused for 20 times, the recoveries of the analyzed ions enriched by the fiber were still over 95% (except for Hg(III)). One thousand-fold excesses of Mn²⁺, Ca²⁺, Zn²⁺, Mg²⁺, Fe³⁺, Cu²⁺, Ni²⁺, Al³⁺, and Ba²⁺ ions and thousands-fold excesses of Na⁺ and K⁺ cause little interference in the pre-concentration and determination of the analyzed ions. The saturated adsorption capacity of Bi(III), Hg(III), Au(III), and Pd(IV) was 4.850×10^–4, 3.235×10^–4, 2.807×10^–4, and 3.386×10^–4 mol g^–1, respectively. The constants of adsorption rate were 0.409 min^–1 for Bi, 0.122 min^–1 for Hg, 0.039 min^–1 for Au, and 0.080 min^–1 for Pd. The relative standard deviations (RSDs) for the enrichment and determination of 10 ng mL^–1 Bi(III), Hg(III), Au(III), and Pd(IV) were lower than 2.3%. The results obtained for these ions in actual samples by this method were basically in agreement with the given values with average errors of less than 1.0%. FT-IR spectra shows that the existence of –SO₂–Ar, –H₂N–Ar, O=C–NH–, HN=C–NH–, and –HN–SO₂ functional groups are verified in the chelating fiber. From the FT-IR spectroscopy, we can see that Hg(III), Au(III), and Pd(IV) are mainly combined with nitrogen and sulfur (or oxygen), and Bi(III) is mainly combined with nitrogen (or oxygen) of the groups to form a chelating complex.