Anton Meden

Air-stable monodispersed Mo6S3I6 nanowires

We report on the properties of a new air-stable nanowire material with the chemical formula Mo6S3I6 .T he distinguishing features of the material are rapid one-step synthesis, easy isolation and controllable dispersion into small-diameter wire bundles. Elemental analysis, x-ray diffraction, thermogravimetry, differential thermal analysis, Raman scattering and electron microscopy were used to characterize the material.

Atomic and electronic structure of Mo6S9−xIx nanowires

Moybdenum-based subnanometre diameter nanowires are easy to synthesize and disperse, and they exhibit a variety of functional properties in which they are superior to other one-dimensional materials. However, further progress in the understanding of physical properties and the development of new and specific applications have so far been impeded by the fact that their structure was not accurately known. Here we report on a combination of systematic x-ray diffraction and extended x-ray absorption fine structure experiments, and first-principles theoretical structure calculations, which are used to determine the atomic skeletal structure of individual Mo6S9−xIx (MoSIx) nanowires, their packing arrangement within bundles and their electronic band structure. From this work we conclude that the variations in functional properties appear to arise from different stoichiometry, not skeletal structure. A supplementary data file is available from http://stacks.iop.org/0957-4484/16/1578

Detailed In Situ Investigation of the Electrochemical Processes in Li2FeTiO4 Cathodes

The possible mechanism of lithium exchange from Li 2 FeTiO 4 is discussed on the basis of three different in situ structural characterization methods. The in situ X-ray diffraction (XRD) showed that the mechanism of lithium exchange was through a solid solution formation whereby the change in volume during the oxidation was 1.4%. The reversibility in terms of charge recuperation was complete; however, after the first reduction, the change in volume was still 0.4%. In situ Mossbauer spectroscopy experiment showed complete Fe(II) oxidization to Fe(III), while the reduction was not reversible. After the complete first cycle, the number of local environments in the Mossbauer spectra needed for a successful fit increased by at least two. Several local environments can be explained on the basis of extended X-ray absorption fine structure results. In the as-prepared sample, Fe cations are coordinated to three oxygen atoms at 2.03 A and another three at 2.13 A. With the oxidation of Fe, the splitting of two oxygen atoms gradually increases to 0.18 A, and the octahedra deformation gradually changes from 3 + 3 to 4 + 2. This deformation is not reversible and it can explain changes in the long-range order as observed from in situ XRD.

Synthesis and Self-Assembly of Thio Derivatives of Calix[4]arene on Noble Metal Surfaces

Self-assembled monolayers (SAMs) provide a simple route to functionalize electrode surfaces with organic molecules. Herein we use cavity-containing derivatives of calix[4]arenes in SAMs. Bound to noble metal surface, the assembled molecules are candidates to serve as molecular sieves for H 2 molecules and H (+) ions, which could have relevance for fuel cell applications. Tetra- O-alkylated calix[4]arenes with thiolacetate and thiolamide wide-rim anchoring groups in cone and partial-cone conformations were designed, synthesized and self-assembled onto Au, Pt, and Pd surfaces. The resulting SAMs were systematically examined. Single crystal X-ray diffraction of 5,11,17,23-tetrakis(thioacetyl)-25,26,27,28-tetra- i-propoxycalix[4]arene confirmed the cone conformation and revealed the cavity dimensions of the SAMs that were formed by immersing noble metal substrates (Au, Pt and Pd deposited on Si-wafers) in solutions of calix[4]arenes. Surface characterization techniques including ellipsometry, cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS) were used, indicating that the metal surface is terminated with a monomolecular layer. Experimental thicknesses obtained from the ellipsometry are consistent with the calculated values. CV results showed 50 to 80% physical passivation against the Fe(CN) 6 (3-/4-) couple, implying an overall relatively low concentration of defects and pinholes in the films. The binding energies of the S2p core level in the XPS were consistent with the literature values and revealed that up to 3.2 out of four anchoring groups were bonded to the noble metal surface.

Stereoselective synthesis of (1R,3R,4R)-3-(1,2,4-triazolo[4,3-x]azin-3-yl)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-ones

Abstract (1R,3R,4R)-3-(1,2,4-Triazolo[4,3-x]azin-3-yl)-1,7,7-trimethylbicyclo[2.2.1]heptan-2-ones were prepared in 68–94% d.e. in three steps from (1R)-(+)-camphor via coupling of (1R,4R)-3-[(E)-(dimethylamino)methylidene]-1,7,7-trimethylbicyclo[2.2.1]heptan-2-one with hydrazinoazines followed by oxidative cyclisation of the intermediate hydrazones with methanolic bromine. The structures were determined by 2D NMR techniques and NOESY spectroscopy as well as by X-ray diffraction.

Synthesis and Characterization of VIVO Complexes of Picolinate and Pyrazine Derivatives. Behavior in the Solid State and Aqueous Solution and Biotransformation in the Presence of Blood Plasma Proteins

Oxidovanadium(IV) complexes with 5-cyanopyridine-2-carboxylic acid (HpicCN), 3,5-difluoropyridine-2-carboxylic acid (HpicFF), 3-hydroxypyridine-2-carboxylic acid (H2hypic), and pyrazine-2-carboxylic acid (Hprz) have been synthesized and characterized in the solid state and aqueous solution through elemental analysis, IR and EPR spectroscopy, potentiometric titrations, and DFT simulations. The crystal structures of the complexes (OC-6-23)-[VO(picCN)2(H2O)]·2H2O (1·2H2O), (OC-6-24)-[VO(picCN)2(H2O)]·4H2O (2·4H2O), (OC-6-24)-Na[VO(Hhypic)3]·H2O (4), and two enantiomers of (OC-6-24)-[VO(prz)2(H2O)] (Λ-5 and Δ-5) have been determined also by X-ray crystallography. 1 presents the first crystallographic evidence for the formation of a OC-6-23 isomer for bis(picolinato) V(IV)O complexes, whereas 2, 4, and 5 possess the more common OC-6-24 arrangement. The strength order of the ligands is H2hypic ≫ HpicCN > Hprz > HpicFF, and this results in a different behavior at pH 7.40. In organic and aqueous solution the three isomers OC-6-23, OC-6-24, and OC-6-42 are formed, and this is confirmed by DFT simulations. In all the systems with apo-transferrin (VO)2(apo-hTf) is the main species in solution, with the hydrolytic V(IV)O species becoming more important with lowering the strength of the ligand. In the systems with albumin, (VO)(x)HSA (x = 5, 6) coexists with VOL2(HSA) and VOL(HSA)(H2O) when L = picCN, prz, with [VO(Hhypic)(hypic)](-), [VO(hypic)2](2-), and [(VO)4(μ-hypic)4(H2O)4] when H2hypic is studied, and with the hydrolytic V(IV)O species when HpicFF is examined. Finally, the consequence of the hydrolysis on the binding of V(IV)O(2+) to the blood proteins, the possible uptake of V species by the cells, and the possible relationship with the insulin-enhancing activity are discussed.

EXAFS and NMR investigation of zinc, manganese and cobalt substituted aluminophosphates with the chabazite structure

Abstract Zinc, manganese and cobalt containing aluminophosphates with the chabazite (CHA) structure type (MeAPO-34, MeZn, Mn and Co) have been synthesized hydrothermally in the presence of tetraethylammonium hydroxide. All samples showed a very high crystallinity without impurity phases, as evidenced by X-ray diffraction and scanning electron microscopy. The results of EXAFS spectroscopy on as-synthesized samples show that the metals possess 4 oxygen atoms in the first coordination shell which is an indication for a tetrahedral coordination in the lattice. The decrease of the EXAFS amplitude for some samples upon calcination is in agreement with the presence of Lewis acid sites, as previously reported. 31P NMR confirmed the incorporation of metals in the AlPO4-34 structure. For Zn and Mn, the 31P NMR spectra show various lines attributed to different P(nAl, 4-nMe) units and the calculation of the fraction of metal in the samples after deconvolution of the spectra is in very good agreement with elemental analysis. Comparison of the relative intensities of the lines with those obtained by a binomial theorem showed that metals randomly substitute Al in the AlPO4-34 framework. Incorporation of Co in the samples was suggested by a strong decrease in both T1 and T2 relaxation times with respect to SAPO-34 or ZnAPO-34, thus confirming EXAFS data.

π-Stacking of quinoid rings in crystals of alkali diaqua hydrogen chloranilates

The alkali diaqua complexes of hydrogen chloranilic acid of [KHCA(H2O)2], [RbHCA(H2O)2] and [CsHCA(H2O)2], and the salt of NH4HCA·2H2O were prepared and their crystal structures determined. The homologues of lithium and sodium are not stable, but their analogues [LiHCAEtOH] and [Na5HCA(CA)2(H2O)10] were obtained. All crystal structures studied, with exception of [LiHCAEtOH], reveal 3D-hydrogen bond networks with pronounced π⋯π interactions between anions supported by attractive polar interactions; the shortest separation distance between the centroids [3.229(2) A] of the hydrogen chloranilate rings in a face-to-face stack is observed in the structure of [KHCA(H2O)2]. The analysis presented is focused on noncovalent interactions, in particular, the influence of cations and hydrogen bonds on the π-stacking of quinoid rings.

1,3-Dipolar Cycloadditions to (5Z)-1-Acyl-5-(cyanomethylidene)- imidazolidine-2,4-diones: Synthesis and Transformations of Spirohydantoin Derivatives

Cycloadditions of various 1,3-dipoles to (5Z)-1-acyl-5-(cyanomethylidene)-3-methylimidazolidine-2,4-diones 8 or 9, prepared in 3 steps from hydantoin (1) (Schemes 1 and 2), were studied. In all cases, reactions proceeded regio- and stereoselectively. The type of product depended on the 1,3-dipole and/or dipolarophile employed as well as on reaction conditions. Thus, with stable dipoles under neutral conditions, spirohydantoin derivatives 12 – 16 were obtained (Scheme 2), while under basic or acidic conditions, pyrazole- or isoxazole-5-carboxamides 18 and 23 – 26 and carboxylate 27 were formed via aromatization of the newly formed dihydroazole ring, followed by the simultaneous cleavage of the hydantoin ring (Schemes 3 – 5).

Recycling of ladle slag in cement composites: Environmental impacts.

In the present work compact and ground cement composites in which 30% of cement by mass was replaced by ladle slag were investigated for their chemical and physico-mechanical properties. To evaluate long-term environmental impacts, leachability test based on diffusion, which combined both, diffusion and dissolution of contaminants, was performed in water and saline water. Total element concentrations and Cr(VI) were determined in leachates over a time period of 180days. At the end of the experiment, the mineralogical composition and the physico-mechanical stability of cement composites was also assessed. The results revealed that Cr(III) and Cr(VI) were immobilized by the hydration products formed in the cement composites with the addition of ladle slag. Cr(VI) content originating from the cement was also appreciably reduced by Fe(II) from minerals present in the added ladle slag, which thus had significant positive environmental effects. Among metals, only Mo and Ba were leached in elevated concentrations, but solely in ground cement composites with the addition of ladle slag. Lower V concentrations were observed in leachates of ground than compact composite. It was demonstrated that the presence of ladle slag in cement composites can even contribute to improved mortar resistance. The investigated ladle slag can be successfully implemented in cement composites as supplementary cementitious material.