Experimental and four‐component relativistic DFT studies of tungsten carbonyl complexes

We present a theoretical and experimental study of the structure and nuclear magnetic resonance (NMR) parameters of the pentacarbonyltungsten complexes of η¹‐2‐(trimethylstannyl)‐4,5‐dimethylphosphinine, η²‐norbornene, and imidazolidine‐2‐thione. The three complexes have a pseudo‐octahedral molecular structure with the six ligands bonded to the tungsten atom. The η¹‐2‐(trimethylstannyl)‐4,5‐dimethylphosphinine‐pentacarbonyl tungsten complex was synthesized for the first time. For all compounds, we present four‐component relativistic calculations of the NMR parameters at the Dirac–Kohn–Sham density functional level of theory using hybrid functionals. These large‐scale relativistic calculations of NMR chemical shifts and spin–spin coupling constants were compared with available experimental data, either taken from the literature or measured in this work. The inclusion of solvent effects modeled using a conductor‐like screening model was found to improve agreement between the calculated and experimental NMR parameters, and our best estimates for the NMR parameters are generally in good agreement with available experimental results. The present work demonstrates that four‐component relativistic theory has reached a level of maturity that makes it a convenient and accurate tool for modeling and understanding chemical shifts and indirect spin–spin coupling constants of organometallic compounds containing heavy elements, for which conventional non‐relativistic theory breaks down. Copyright © 2015 John Wiley & Sons, Ltd.     

Preparation and Characterization of Protonated Fumaric Acid

Fumaric acid was reacted with the binary superacidic systems HF/SbF₅ and HF/AsF₅. The O,O'-diprotonated [C₄H₆O₄]²⁺([MF₆]^–)₂ (M = As, Sb) and the O-monoprotonated [C₄H₅O₄]⁺[MF₆]^– (M = As, Sb) species are formed depending on the stoichiometric ratio of the Lewis acid to fumaric acid. The colorless salts were characterized by low-temperature vibrational spectroscopy. In case of the hexafluoridoantimonates single-crystal X-ray structure analyses were carried out. The [C₄H₆O₄]²⁺([SbF₆]^–)₂ crystallizes in the monoclinic space group C2/c with four formula units per unit cell and [C₄H₅O₄]⁺[SbF₆]^– crystallizes in the triclinic space group P1 with one formula unit per unit cell. The protonation of fumaric acid does not cause a notable change of the C=C bond length. The experimental data are discussed together with quantum chemical calculations of the cations [C₄H₆O₄ · 4 HF]²⁺ and [C₄H₆O₄ · 2 H₂CO · 2 HF]²⁺.     

The blogosphere as an excitable social medium: Richter’s and Omori’s Law in media coverage

We study the dynamics of public media attention by monitoring the content of online blogs. Social and media events can be traced by the propagation of word frequencies of related keywords. Media events are classified as exogenous–where blogging activity is triggered by an external news item–or endogenous where word frequencies build up within a blogging community without external influences. We show that word occurrences exhibit statistical similarities to earthquakes. Moreover the size distribution of events scales with a similar exponent as found in the Gutenberg–Richter law. The dynamics of media events before and after the main event can be satisfactorily modeled as a type of process which has been used to understand fore–and aftershock rate distributions in earthquakes–the Omori law. We present empirical evidence that for media events of endogenous origin the overall public reception of the event is correlated with the behavior of word frequencies at the beginning of the event, and is to a certain degree predictable. These results imply that the process of opinion formation in a human society might be related to effects known from excitable media.     

A convenient synthesis of optically active 5,5-disubstituted 4-amino- and 4-hydroxy-2(5H)-furanones from (S)-ketone cyanohydrins

(S)-Ketone cyanohydrins (S)-2 are accessible by enantioselective HCN addition to ketones 1 by using hydroxynitrile lyase from Manihot esculenta ((S)-MeHNL) as a biocatalyst. Acylation of (S)-2 gave the corresponding (S)-acyloxynitriles (S)-3, which can be cyclized by LHMDS to give 5,5-disubstituted (S)-4-amino-2(5H)-furanones (S)-4 and (S)-5. Different substituents (H. Me, OBn, OH) in the 3-position of the furanones were introduced by selecting the appropriate acylating agent, which in the case of benzyloxyacetyl chloride led to the novel structure type of 4-amino-3-hydroxyfuranones (S)-5. For the synthesis of 5,5-disubstituted (S)-tetronic acids (S)-8, ketone cyanohydrins (S)-2 were first transformed into the corresponding 2-hydroxy esters (S)-6. Acylation of (S)-6 gave 2-acyloxy esters (S)-7, which, by treatment with LHMDS or LDA, afforded tetronic acids (S)-8 in high yields and enantiomeric excesses. By debenzylation of benzyloxy acetoxy derivatives (S)-8e,f, the new vitamin C analogues (S)-9a,b were generated. All the described tetronic acid and aminofuranone derivatives were obtained in good chemical yields and without racemization with respect to the starting cyanohydrins (S)-2. In many cases the enantiomeric purity could be enriched by simple recrystallization (e.g. (S)-4a from 69% ee to > 99% ee).     

Zur Bestimmung von freien o- und p-Stellungen in Methyl- und Phenyl-sulfonylphenolen

Ohne Zusammenfassung     

Control of vertically coupled InGaAs/GaAs quantum dots with electric fields

Controllable interactions that couple quantum dots are a key requirement in the search for scalable solid state implementations for quantum information technology. From optical studies of excitons and corresponding calculations, we demonstrate that an electric field on vertically coupled pairs of In(0.6)Ga(0.4)As/GaAs quantum dots controls the mixing of the exciton states on the two dots and also provides controllable coupling between carriers in the dots.