Publikationen

The molecular structure of trans-dichlorodioxobis(triphenylphosphate) molybdenum(VI), MoO2Cl2[OP(OPh)3]2 has been determined. Crystal data: Monoclinic, Pn, a = 11.767(2), b = 10.341(2), c = 15.682(3) Å, β = 92.27(3)°, V = 1906.8(7) Å-3, Z = 2. Trans-dichlorodioxobis(triphenylphosphate)molybdenum(VI) was obtained by the reaction of molybdenum oxide, HCl and triphenylphosphate and was characterized by elemental analysis, IR, and 1H-NMR spectroscopy.

The dinuclear gold complexes [{Au(PPh3)}2(µ-dmid)] (1) (dmid) 1,3-dithiole-2-one-4,5-dithiolate) and [{Au(PPh3)}2(µ-dddt)] (2) (dddt) 5,6-dihydro-1,4-dithiine-2,3-dithiolate) were synthesized and characterized by X-ray crystallography. Both complexes exhibit intramolecular aurophilic interactions with Au · · · Au distances of 3.1984(10) Å for 1 and 3.1295(11) Å for 2. A self-assembly reaction between 4,5-bis(2-hydroxyethylthio)-1,3-dithiole-2-thione ((HOCH2CH2)2dmit) and [AuCl(tht)] affords the complex [AuCl{(HOCH2CH2)2dmit}]2 (4), which possesses an antiparallel dimeric arrangement resulting from a short aurophilic contact of 3.078(6) Å. This motif is extended into two dimensions due to intra- and intermolecular hydrogen bonds via the hydroxyethyl groups, giving rise to a supramolecular network. Three compounds were investigated for their rich photophysical properties at 298 and 77 K in 2-MeTHF and in the solid state; [Au2(µ-dmid)(PPh3)2] (1), [Au2(µ-dddt)(PPh3)2] (2), and [AuCl{(HOCH2CH2)2dmit}] (4). 1 exhibits relatively long-lived LMCT (ligand-to-metal charge transfer) emissions at 298 K in solution (370 nm; τe ∼17 ns, where M is a single gold not interacting with the other gold atom; i.e., the fluxional C-SAuPPh3 units are away from each other) and in the solid state (410 nm; τe ∼70 µs). At 77 K, a new emission band is observed at 685 nm (τe = 132 µs) and assigned to a LMCT emission where M is representative for two gold atoms interacting together consistent with the presence of Au · · · Au contacts as found in the crystal structure. In solution at 77 K, the LMCT emission is also red-shifted to 550 nm (τe ∼139 µs). It is believed to be associated to a given rotamer. 2 also exhibits LMCT emissions at 380 nm at 298 K in solution and at 470 nm in the solid state. 4 exhibits X/MLCT emission (halide/metal to ligand charge transfer) where M is a dimer in the solid state with obvious Au · · · Au interactions, resulting in red-shifted emission band, and is a monomer in solution in the 10-5 M concentration (i.e., no Au · · · Au interactions) resulting in blue-shifted luminescence. Both fluorescence and phosphorescence are observed for 4.

Six new methyl silicon (IV) precursors of the type [MeSi{ON=C(R)Ar}3] [when R = Me, Ar = 2-C5H4N (1), 2-C4H3O (2) or 2-C4H3S (3); and when R = H, Ar = 2-C5H4N (4), 2-C4H3O (5) or 2-C4H3S (6)] were prepared and structurally characterized by various spectroscopic techniques. Molecular weight measurements and FAB (Fast Atomic Bombardment) mass spectral studies indicated their monomeric nature. 1H and 13C{1H} NMR spectral studies suggested the oximate ligands to be monodentate in solution, which was confirmed by 29Si{1H} NMR signals in the region expected for tetra-coordinated methylsilicon (IV) derivatives. Thermogravimetric analysis of 1 revealed the complex to be thermally labile, decomposing to a hybrid material of definite composition. Two representative compounds (2 and 4) were studied as single source molecular precursor for low-temperature transformation to silica-based hybrid materials using sol-gel technique. Formation of homogenous methyl-bonded silica materials (MeSiO3/2) at low sintering temperature was observed. The thermogravimetric analysis of the methylsilica material indicated that silicon-methyl bond is thermally stable up to a temperature of 400 °C. Reaction of 2 and Al(OPri)3 in equimolar ratio in anhydrous toluene yielded a brown-colored viscous liquid of the composition [MeSi{ON=C(CH3)C4H3O}3.Al(OPri)3]. Spectroscopic techniques 1H, 13C{1H}, 27Al{1H} and 29Si{1H} NMR spectra of the viscous product indicated the presence of tetracoordination around both silicon and aluminum atoms. On hydrolysis it yielded methylated aluminosilicate material with high specific surface area (464 m2/g). Scanning electron micrography confirmed a regular porous structure with porosity in the nanometric range.

6×8 cm2 electrochromic devices (ECDs) with the configuration K-glass/EC-layer/electrolyte/ion-storage (IS) layer/K-glass, have been assembled using Nb2O5:Mo EC layers, a (CeO2)0.81-TiO2 IS-layer and a new gelatin electrolyte containing Li+ ions. The structure of the electrolyte is X-ray amorphous. Its ionic conductivity passed by a maximum of 1.5×10−5 S/cm for a lithium concentration of 0.3 g/15 ml. The value increases with temperature and follows an Arrhenius law with an activation energy of 49.5 kJ/mol. All solid-state devices show a reversible gray coloration, a long-term stability of more than 25,000 switching cycles (±2.0 V/90 s), a transmission change at 550 nm between 60% (bleached state) and 40% (colored state) corresponding to a change of the optical density (ΔOD=0.15) with a coloration efficiency increasing from 10 cm2/C (initial cycle) to 23 cm2/C (25,000th cycle).

Dispersions of three different types of zirconia nanoparticles were treated in a stirred media mill. The deployed surface modifier was present during milling and it established separating mechanisms between the particles. The combination of mechanical deagglomeration and chemical surface modification results in stable zirconia colloids with average particle sizes down to 9 nm. In addition to deagglomeration, the milling treatment also causes comminution of nanoparticles. This was indicated for the two coarser types of the examined particles, by increasing surface areas and decreasing primary crystallite sizes. Transmission electron microscopy of the particles confirmed the creation of smaller primary crystallites and a minority of small fragments, but the majority of particles do not undergo comminution into halves or fragments with similar size. Changes of the particles’ phase composition, wear of milling media, amorphization of the particles to a small extent, and leaching of Y2O3 dopant have been observed as side effects in the process and are characterized quantitatively. This work describes a process for nanoparticle deagglomeration and preparation of high quality colloids, and informs about occurring side effects, including approaches for their minimization.

Nanocomposites of titanium dioxide (TiO2) and multi-walled carbon nanotubes (MWNTs) were prepared and deposited by sol-gel spin coating on borosilicate substrates and sintered in air at 300 °C for 15 min. Further irradiation of the films with different CO2 laser intensities (4.3-17 W m-2) was carried out in order to crystallize TiO2 in the anatase form while preserving the MWNT's structure. The laser irradiation changed the crystal structure of the coatings and also affected the wettability and photocatalytic activity of the films. The anatase phase was only observed when a minimum laser intensity of 12.5 W m-2 was used. The contact angle decreased with the enhancement of the laser intensity. The photocatalytic activity of the films was determined from the degradation of a stearic acid layer deposited on the films. It was observed that the addition of carbon nanotubes themselves increases the photocatalytic activity of TiO2 films. This efficiency is even improved when high CO2 laser intensities are used during the sintering of the coatings.

The role of oxygen diffusion in the response of individual SnO2 nanowires to this gas is studied. Different oxygen partial pressures lead to strong changes of their electrical resistance, even at room temperature. Since surface models fail to explain the experimentally observed long-term resistance transients, it is necessary to make a description of the interaction mechanisms between oxygen species and SnO2 nanowires by taking ion diffusion into account. Our model correctly describes the experimentally measured dependence of the nanowire resistance with oxygen partial pressure, and it can be applied to the characterization of other metal oxide materials.