The elusive structure of CrCl(2): a combined computational and gas-phase electron-diffraction study

Chromium dichloride poses a challenge to the structural chemist. Its different forms of aggregation and association display all well-known structural distortions induced by vibronic interactions. The monomeric molecule has a Renner-Teller distorted bent geometry, the crystal exhibits strong Jahn-Teller distortion, and the oligomers have slightly distorted four-membered-ring structures due to the pseudo-Jahn-Teller effect. In this paper we report on the low-energy structures of the monomer and its clusters, Cr(2)Cl(4), Cr(3)Cl(6), and Cr(4)Cl(8), from unrestricted Kohn-Sham (broken-symmetry) density functional calculations. CrCl(2) was also investigated at higher level, including coupled-cluster and state-average CASSCF computations. The global minima of the gas-phase clusters consist of two-dimensional, antiferromagnetically coupled chains of CrCl(2) units forming four-membered, doubly bridged Cr(2)Cl(2) rings, closely resembling the solid-state structure of alpha-CrCl(2). Each Cr atom in these chains has spin quantum number S=2. This suggests that the CrCl(2) nucleation starts very early on the structural chain motif found in the solid. There is only a very small change in energy from the antiferromagnetically to the ferromagnetically coupled Cr atoms, which indicates little spin-coupling between the metal centers. There is an approximately constant change in energy, about 50 kcal mol(-1), with every new CrCl(2) unit during cluster formation. Information about the structure of these clusters was used in the re-analysis of high-temperature electron-diffraction data. The vapor at 1170 K contained about 77 % monomeric molecules, 19 % dimers, and a small amount of trimers. Monomeric CrCl(2) was found to be bent with a bond angle of 149(10) degrees, in good agreement with our computations, which resulted in a Renner-Teller distortion of the lowest-energy (5)Pi(g) electronic state into the bent (5)B(2) ground state. The vibrational spectrum of chromium dichloride is discussed and the thermodynamics of cluster formation from 1000-2000 K is examined.     

Solventextraktion von Platinmetallen mit N-mono-und N,N-di-substituierten Benzoylthioharnstoffen

Summary Benzoylthioureas are excellent reagents for solvent extraction and have a high selectivity for platinum-group metals. Very effective separations of platinum-group metals are possible due to control of the extraction parameters and variation of the ligand structure. An easy synthesis and a high chemical resistence allow technical applications.

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Herrn Prof. Dr. G. Tölg zum 60. Geburtstag gewidmet     

Hamiltonian traffic dynamics in microfluidic-loop networks

Recent microfluidic experiments revealed that large particles advected in a fluidic loop display long-range hydrodynamic interactions. However, the consequences of such couplings on the traffic dynamics in more complex networks remain poorly understood. In this Letter, we focus on the transport of a finite number of particles in one-dimensional loop networks. By combining numerical, theoretical, and experimental efforts, we evidence that this collective process offers a unique example of Hamiltonian dynamics for hydrodynamically interacting particles. In addition, we show that the asymptotic trajectories are necessarily reciprocal despite the microscopic traffic rules explicitly break the time-reversal symmetry. We exploit these two remarkable properties to account for the salient features of the effective three-particle interaction induced by the exploration of fluidic loops.     

The Direct Conversion of Carboxylic Acids to Carboxamides via Reaction with Unsolvated Bis(Diorganoamino) Magnesium Reagents

It has been found that unsolvated bis (diorganoamino) magnesium compounds react smoothly with carboxylic acids to give the corresponding carboxamides directly in good to excellent yields.     

Sampling and analysis of pesticides in the environment.

Environmental monitoring is now recognized as essential in areas of pesticide use in order to assess the impact of these pesticides on the environment. During the last two decades, advances in instrumentation in terms of detection limits and specificity, along with the growing expertise of residue chemists, have made reports of pesticide residue levels in the parts per billion range commonplace. Using this technical ability and carefully assessing the significance of the data obtained, pesticides can be used in a more efficacious manner with less possible damage to the environment.     

Microscopic mechanism of decomposition of Fe-doped β″-alumina

The role of conduction layers in a decomposition process of Fe-doped β″-alumina into Na-ferrite and spinel in a reducing atmosphere was investigated by means of high resolution transmission electron microscopy. The decomposition starts as diffusion of Na ions out from conduction layers of decomposing β″-alumina into surrounding β″-alumina, causing the collapsing of conduction layers. This leads to a removal of some oxygen ions which is accompanied by a change of Fe³⁺ ions to Fe²⁺ ions. The reaction further proceeds as the formation of precipitates of Na-ferrites and as the reconstruction around the conduction layers, resulting in the formation of spinel. A reverse reaction of the decomposed phases into β″-alumina occurs by annealing in air. Individual conduction layers are recreated in spinel by the flow of ions from the remaining β″-alumina and precipitated Na-ferrite, leading to the recovery into β″- alumina, along with a reverse change of Fe²⁺ to Fe³⁺.     

Extreme-ultraviolet metrology at SURF III

Inelastic X-ray scattering (IXS) is a general experimental technique for studying lattice and electronic excitations, which has undergone rapid development following the advent of the third generation synchrotron radiation facilities. X-ray Raman scattering (XRS) is inelastic scattering of X-rays due to the excitation associated with bound electrons in an atom. Its very small scattering cross-section is compensated for by a high-flux beam generated from a strong photon source. Instrumentation for IXS is now highly sophisticated, and has been applied to study a broad range of condensed matter systems [1 Schülke, e.g., W., ed. 2007. “We would like to limit our discussion to electronic excitations. For a comprehensive survey in the field, see”. In Electron Dynamics by Inelastic X-ray Scattering, New York: Oxford University Press.  [Google Scholar]].     

Turbulent flow visualization by interferometric integral imaging and computed tomography

An experimental system using integral interferometric imaging and computer tomography for visualizing the structure of a turbulent, vertical helium jet is described. Integral images and tomographic integral data were obtained using a pulsed phase-shifted interferometer. The integral images revealed a sinuous overall jet structure and large-scale buckling motions in the far-field. Tomographic reconstruction of jet cross-sections at numerous axial locations were made for three turbulent jets at two different Reynols numbers, 2,800 and 4,300. Tomographic images revealed unmixed ambient fluid far inside the jet boundary and a bimodal concentration distribution. Image interpretation and experimental errors are discussed.