Christian B. Fischer

Trinuclear rhodium hydride complexes

Three novel trinuclear rhodium hydride complexes of the type {[Rh(PP*)H](3)(μ(2)-H)(3)(μ(3)-H)}[BF(4)](2) containing diphosphines Tangphos, t-Bu-BisP* and Me-DuPHOS have been synthesised. The new compounds are very stable. Their structures have been characterized by X-ray analysis in the solid state and by NMR-spectroscopic investigations in solution.

Investigations into the formation and stability of cationic rhodium diphosphane η6-arene complexes.

Rhodium-η(6)-arene complexes can be generated in the presence of arenes following the hydrogenation of the diolefin in rhodium catalyst precursors of the type [Rh(PP*)(diolefin)]X (PP* = chelating diphosphane, X = noncoordinating anion). In this paper we report the characterization of such arene complexes with the ligands DuPhos, dipamp, dppe, Tangphos, dppf, and diop by means of NMR spectroscopy ((31)P, (103)Rh) and X-ray analysis. A procedure that follows the approach to equilibrium as a function of time monitored by using an UV/Vis diode array was used to determine 20 stability constants. Analyses were accomplished directly from the spectra by either a numeric and/or a new analytic solution of the underlying system of differential equations. Additionally thermodynamic parameters were determined in the temperature range between 278 and 318 K.

Time-dependent growth of crystalline Au0-nanoparticles in cyanobacteria as self-reproducing bioreactors: 2. Anabaena cylindrica

Summary Microbial biosynthesis of metal nanoparticles as needed in catalysis has shown its theoretical ability as an extremely environmentally friendly production method in the last few years, even though the separation of the nanoparticles is challenging. Biosynthesis, summing up biosorption and bioreduction of diluted metal ions to zero valent metals, is especially ecofriendly, when the bioreactor itself is harmless and needs no further harmful reagents. The cyanobacterium Anabaena cylindrica (SAG 1403.2) is able to form crystalline Au0-nanoparticles from Au3+ ions and does not release toxic anatoxin-a. X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and laser-induced breakdown spectroscopy (LIBS) are applied to monitor the time-dependent development of gold nanoparticles for up to 40 hours. Some vegetative cells (VC) are filled with nanoparticles within minutes, while the extracellular polymeric substances (EPS) of vegetative cells and the heterocyst polysaccharide layer (HEP) are the regions, where the first nanoparticles are detected on most other cells. The uptake of gold starts immediately after incubation and within four hours the average size remains constant around 10 nm. Analyzing the TEM images with an image processing program reveals a wide distribution for the diameter of the nanoparticles at all times and in all regions of the cyanobacteria. Finally, the nanoparticle concentration in vegetative cells of Anabaena cylindrica is about 50% higher than in heterocysts (HC). These nanoparticles are found to be located along the thylakoid membranes.

Morphological and Chemical Evolution of Gradually Deposited Diamond-Like Carbon Films on Polyethylene Terephthalate: From Subplantation Processes to Structural Reorganization by Intrinsic Stress Release Phenomena

Diamond-like carbon (DLC) films on polyethylene terephthalate (PET) are nowadays intensively studied composites due to their excellent gas barrier properties and biocompatibility. Despite their applicative features being highly explored, the interface properties and structural film evolution of DLC coatings on PET during deposition processes are still sparsely investigated. In this study two different types of DLC films were gradually deposited on PET by radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) using acetylene plasma. The surface morphology of the deposited samples has been analyzed by atomic force microscopy (AFM). Their chemical composition was investigated by diffusive reflectance infrared Fourier transform (DRIFT) and Raman spectroscopy analysis and the surface wettability by contact angle measurements. Subplantation processes and interface effects are revealed through the morphological and chemical analysis of both types. During plasma deposition processes the increasing carbon load causes the rise of intrinsic film stress. It is proven that stress release phenomena cause the transition between polymer-like to a more cross-linked DLC network by folding dehydrogenated chains into closed 6-fold rings. These findings significantly lead to an enhanced understanding in DLC film growth mechanism by RF-PECVD processes.

Investigations into Metal Leaching from Polystyrene-Supported Rhodium Catalysts

The anchoring of molecularly well‐defined Rh complexes on a solid support allows the combination of the advantages of homogeneous catalysis with the benefit of catalyst recycling offered by heterogeneous catalysis. Unfortunately, the common approach to attach the soluble Rh catalyst onto a variety of polystyrene supports has not in general led to useful catalysts, and a major problem is metal leaching into the solution. We report herein that, besides the binding of the Rh catalysts to the polymeric matrix, in principle η6‐aromatic complexes can also be formed, as shown by NMR spectroscopy and XRD. The stability constants of such complexes for styrene and soluble polystyrenes (PS4000, 38.4 monomers and PS30000, 288 monomers) have been measured by UV/Vis spectroscopic titrations. The establishment of equilibrium with the Rh‐solvent complex is very rapid to the point that, after the anchoring of the catalyst to the polystyrene matrix, the rinsing of the material with solvent during work‐up causes part of the Rh coordinated originally as an aromatic complex to be washed away.

(+)-{1,2-Bis[(2R,5R)-2,5-dimethyl-phospho-lan-1-yl]ethane-κP,P'}(η-cyclo-octa-1,5-diene)rhodium(I) tetra-fluorido-borate.

The title compound, [Rh(C8H12)(C14H28P2)]BF4, exhibits a rhodium(I) complex cation with a bidentate bisphosphine ligand and a bidentate η2,η2-coordinated cycloocta-1,5-diene. Together the ligands create a slightly distorted square-planar cordination environment for the Rh(I) atom. There are three molecules in the asymmetric unit and intramolecular P—Rh—P bite angles of 82.78 (5), 82.97 (6) and 83.09 (5)° are observed. The dihedral angles between the P—Rh—P and the X—Rh—X planes (X is the centroid of a double bond) are 14.7 (1), 14.8 (1) and 15.3 (1)°. The structure exhibits disorder of one cyclooctadiene ligand as well as one BF4 anion.

Preparation and Study of Bacterial Layers on SWCNT Films with Subsequent Carbonization

Two types of bacteria were placed on the top surface of carbon nanotube films and the composite film morphology was examined using scanning electron microscopy. The interaction of bacteria with the carbonaceous film was studied after drying and subsequent heating to 1000 °C. For gram-positive bacteria, subsequent shrinkage of the bacterial layer causes film stresses and roll-up, and for the gram-negative bacteria the carbonization step seems to leave residual bacterial-derived material in-between the Single-Walled Carbon NanoTube (SWCNT) network, suggesting some type of interaction between the SWCNTs and the bacterial wall that leads to incorporation of material within the network, which then carbonizes. These observed property changes are undesirable during the lifetime of the material network, but might be welcome for its later disposal.

Synthesis and solid-state structures of alkyl-substituted 3-cyano-2-pyridones

Abstract A series of 3-cyano-pyridones carrying a variety of alkyl substituents at C-5 and C-6 has been synthesized and their solid-state structures have been studied. Hydrogen bonding interactions between individual pyridone molecules lead either to the formation of symmetric dimers of the R22 (8) type or to helical chains of the C(4) type. Based on known and calculated structures for the 2-pyridone parent system, the solid-state structures can be divided in two groups representing cases with little external influence on the hydrogen bonding array (group A) and those with a larger external influence (group B).