(Mn1−xPbx)Pb10+ySb12−yS26−yCl4+yO, a new oxy-chloro-sulfide with ∼2 nm-spaced (Mn,Pb)Cl4 single chains within a waffle-type crystal structure

The new oxy-chloro-sulfide (Mn_1−xPb_x)Pb_10+ySb_12−yS_26−yCl_4+yO (x ∈ [0.2-0.3]; y ∈ [0.3-1.6]) was synthesized by dry way at 500-600 °C. A single crystal ∼Mn_0.7Pb_11.0Sb_11.3S_25.3Cl_4.7O indicates a monoclinic symmetry, space group C2/m, with a = 37.480(8), b = 4.1178(8), c = 18.167(4) Å, β = 106.37(3)°, V = 2690.2(9) Å³, Z = 2. Its crystal structure was determined by X-ray single crystal diffraction, with a final R = 5.11%. Modular analysis of the crystal structure reveals a “waffle” architecture, where complex rods with lozenge section delimitate an internal channel filled by a single chain of (Mn_0.7Pb_0.3)Cl₆ octahedra connected by opposite edges. Minimal inter-chain distances are close to 18 Å. The rod wall, two-atom thick, presents, in alternation with S atoms, Pb or (Pb,Sb) cations with prismatic coordination in the internal atom layer, while the external atom layer is constituted exclusively by Sb cations with dissymmetric square pyramidal coordination. A (Pb,Sb)₂S₂ fragment connects two successive rods along (2 0 1) to form a waffle-type palissadic layer. The unique O position, half filled, presents the same environment than the isolated O positions in the oxy-sulfide Pb₁₄Sb₃₀S₅₄O₅, or oxy-chloro-sulfides Pb₁₈Sb₂₀S₄₆Cl₂O and (Cu,Ag)₂Pb₂₁Sb₂₃S₅₅ClO. This compound belongs to a pseudo-homologous series of chalcogenides with waffle structure, ordered according to the size of their lozenge shape channel. Such a complex senary compound of the oxy-chloro-sulfide type illustrates the structural competition between three cations, on one hand, and, on the other hand, three anions. This compound is of special interest regarding the 1D distribution of magnetic Mn²⁺ atoms at the ∼2 nm scale.     

Determination of microgram quantities of tin(IV) by a combined ion-exchange/X-ray fluorescence technique

A method is described for the analysis of microgram quantities of tin in dilute hydrofluoric acid. The tin is extracted onto anion-exchange resin loaded paper discs by a very simple technique and the papers are examined by X-ray fluorescence spectrography. The solutions are obtained by the dissolution of tin-containing glasses, and the normal glass-forming elements do not interfere. The method is intended for the determination of 1-20 mug of tin but may be used for up to at least 250 mug; 5 mug can be determined with a precision of +/- 10%.     

A correlation study of Li ground state by the MCHF procedure

Results are reported for multiconfiguration Hartree–Fock studies of correlation in the lithium ground state, which maintain orthogonality of orbitals within a configuration. It is shown that when the 1s- and 2s-orbitals are fixed at their Hartree–Fock value, configurations for which Brillouin's theorem holds may be important, particularly for atomic properties other than energy. The Fermi contact term is considered as an example.     

Sulfonamides as novel terminators of cationic cyclisations

Trifluoromethanesulfonic (triflic) acid is an excellent catalyst for inducing overall 5-endo cyclisation of homoallylic sulfonamides [e.g. 4] to give pyrrolidines [e.g. 5]. In competitive experiments, pyrrolidines or homopiperidines are formed in preference to piperidines, even when the latter would be obtained by trapping a tertiary carbocation. Cationic cascades terminated by a sulfonamide group are viable for the efficient formation of polycyclic systems.     

Transparent conducting oxides: texture and microstructure effects on charge carrier mobility in MOCVD-derived CdO thin films grown with a thermally stable, low-melting precursor

A series of low-melting, thermally stable cadmium metal-organic chemical vapor deposition (MOCVD) precursors have been synthesized, structurally and spectroscopically characterized, and implemented in growth of highly conductive and transparent CdO thin films. One member of the series, bis(1,1,1,5,5,5-hexafluoro-2,4-pentanedionato)(N,N-diethyl-N',N'-dimethyl-ethylenediamine)cadmium(II), Cd(hfa)(2)()(N,N-DE-N',N'-DMEDA), represents a particularly significant improvement over previously available Cd precursors, owing to the low melting point and robust thermal stability. High-quality CdO films were grown by MOCVD on glass and single-crystal MgO(100) between 300 and 412 degrees C. Film growth parameters and substrate surface have large effects on microstructure and electron carrier transport properties. Enhanced mobilities observed for highly biaxially textured films grown on MgO(100) vs glass are attributed, on the basis of DC charge transport and microstructure analysis, to a reduction in neutral impurity scattering and/or to a more densely packed grain microstructure. Although single-grained films grown on MgO(100) exhibit greater mobilities than analogues with discrete approximately 100 nm grains and similar texture, this effect is attributed, on the basis of charge transport and Hall effect measurements as well as optical reflectivity analysis, to differences in carrier concentration rather than to reduced grain boundary scattering. Unprecedented conductivities and mobilities as high as 11,000 S/cm and 307 cm(2)/V.s, respectively, are obtained for epitaxial single-grained films (X-ray diffraction parameters: fwhm(omega) = 0.30 degrees, fwhm(phi) = 0.27 degrees ) grown in situ on MgO(100) at a relatively low temperature (400 degrees C).     

Templated ceramic microstructures by using the breath-figure method

We describe the synthesis of two cyclobutadiene(cyclopentadienyl)cobalt-containing poly(p-phenylene ethynylene)s (PPEs) and their use as precursors for stable ceramic surface coatings. Organometallic PPEs were shaped into hexagonally ordered assemblies by using the breath-figure method. Such breath figures can be washed away with an appropriate solvent. Upon pyrolysis at 500 degrees C under either nitrogen or air, the bubble arrays persist as ceramics and are insoluble in organic solvents or water. The formed pyrolyzed bubble arrays were analyzed by optical and scanning electron microscopy, as well as energy dispersive X-ray microanalysis (EDX). The composition of the ceramic materials is discussed based on EDX and IR data.     

Novel metal-linked face-to-face porphyrazine dimer

We report the synthesis and physical studies of a novel porphyrazine (pz) dimer [1[Ni,Cu]]2, which has Ni(II) ions incorporated into the pz cores and is linked by two Cu(II) ions coordinated to bis(picolinamide) chelates attached to the pz periphery. [1[Ni,Cu]]2 was prepared from precursor pz 2 with a selenodiazole ring fused to the pz core. This ring was deprotected to form the diamino-pz 3, which reacted with 2 mol of picolinoyl chloride hydrochloride to form pz 1[2H,2H], with peripheral bis(picolinamide) chelates; this was metalated to form [1[Ni,Cu]]2. The crystal structures of 1[2H,2H] and [1[Ni,Cu]]2 are presented. The latter is a dimer in which parallel, face-to-face pz's with an average separation of 3.30 angstroms are linked through the peripheral picolinamide ligands by a pair of peripheral Cu(II) ions. Each Cu(II) is coordinated with distorted square-planar geometry by a picolinamide from each pz. In this report, we focus on the interaction of these two peripheral Cu(II) ions. We discuss the preparation and magnetic properties of the pz dimer complex [1[Ni,Cu]]2 with two Cu(II) ions in the peripheral chelate but a diamagnetic metal ion Ni(II) in the pz core. Although [1[Ni,Cu]]2 contains two Cu(II) ions (S = 1/2), we could detect no electron paramagnetic resonance signal, which suggests very strong antiferromagnetic exchange between those two Cu(II) ions. Temperature-dependent magnetic susceptibility measurement gives an exchange splitting between the S = 0 ground state and the excited triplet state of delta = 660 cm(-1).     

Electrocatalytic detection of streptomycin and related antibiotics at ruthenium dioxide modified graphite--epoxy composite electrodes

The application of ruthenium dioxide (RuO2) modified electrodes to the electrocatalytic detection of the saccharide-related antibiotics streptomycin, novobiocin and neomycin, at low fixed potentials, was investigated. The RuO2-modified graphite - epoxy composite electrodes give extremely stable and reproducible catalytic oxidation currents for these antibiotics at potentials as low as +0.2 V (versus Ag - AgCl). Rapid quantification at the micromolar level is therefore possible. Standard calibration graphs for streptomycin and neomycin yielded slopes of 4.43 and 0.08 nA microM-1 over the linear ranges of 1.5 x 10(-6) - 2.5 x 10(-4) and 1 x 10(-5) - 2 x 10(-3) M, respectively. Owing to its catalytic oxidation by the RuIII - RuIV couple, rather than the RuIV - RuVI transition (which catalyses the oxidation of streptomycin and neomycin), novobiocin could be detected at a lower (+0.2 V) potential, with a sensitivity of 1.31 nA microM-1. Detection limits of 1.5, 6.0 and 10 microM were obtained for streptomycin, novobiocin and neomycin, respectively. These catalytic surfaces can be renewed (by polishing), with a surface-to-surface reproducibility of 6.5% for the detection of 5 x 10(-5) M streptomycin. The analytical application of RuO2-modified carbon paste electrodes to the analysis of these antibiotics by flow injection was investigated, with a view to liquid chromatographic separation with electrochemical detection applications.     

Ultraviolet emission spectra of sunbeds

It is well known that UV radiation contributes to the development of skin cancer. Exposure to solar radiation is predominantly responsible for the high incidence rate of skin cancer, but there are also indications that sunbeds are involved. The aim of the present investigation was to determine the UV emission spectra of sunbeds. It included the most common sunbed models, which cover more than 50% of the Swiss market. The UV emission spectra of sunbeds have special characteristics and are different from the sun spectrum, which can be seen in high-resolution spectral measurements. Sunbed emission spectra are similar to the sun spectrum in the UVB (280-320 nm) range but reach values 10 to 15 times higher in the UVA (320-400 nm) range. An average erythema-effective irradiance of 0.33 W/m2 was determined for sunbeds. This corresponds to a UV index of 13, which is significantly higher than the UV index of 8.5 of the high summer sun at noon at intermediate latitudes. The measurements were spread over the whole effective area of the sunbeds, and an inhomogeneous distribution of the irradiances with variations of up to 30% from the average value was found.     

SPOCC-194, a new high functional group density PEG-based resin for solid-phase organic synthesis

A novel polymer matrix for solid-phase synthesis, SPOCC(194) resin (1), was designed featuring a backbone of homogeneous tetraethylene glycol (TEG(194)) macromonomer linked by quaternary carbon junctions and terminating in primary alcohol functionality. Beaded SPOCC(194) resin was effectively prepared by suspension polymerization of oxetanylated TEG macromonomer 5 in stirred silicon oil. Mechanically stable and inert to a diverse range of reaction conditions, SPOCC(194) possessed a high hydroxyl group loading (0.9-1.2 mmol/g) for substrate attachment and swelled effectively ( approximately 2-4 mL/g) in a variety of organic and aqueous solvents. Developed for solid-phase synthesis at high reactant concentrations for driving organic and aqueous reactions to completion, SPOCC(194) exhibited high functional group density (mmol/mL) similar to that of low-loaded aminomethylated polystyrene-divinylbenzene copolymer (PS-1%DVB) yet significantly higher than that of PEGA(1900), SPOCC(1500), and TentaGel S. High-resolution MAS NMR spectra of Fmoc-derivatized SPOCC(194) indicate that monitoring of functional group transformation is possible. Moreover, by employment of a nonaromatic resin-linker combination, electrophilic chemistry, such as Lewis acid catalyzed glycosylation and Friedel-Crafts acylation, was selectively performed on substrate bound to SPOCC(194) resin. Such properties make SPOCC(194) resin a promising new polymer matrix for the support-bound construction of small organic molecules by parallel and combinatorial synthesis and the scavenging of solution-phase reactants or byproducts.