Surface state charge dynamics of a high-mobility three dimensional topological insulator

We present a magneto-optical study of the three-dimensional topological insulator, strained HgTe using a technique which capitalizes on advantages of time-domain spectroscopy to amplify the signal from the surface states. This measurement delivers valuable and precise information regarding the surface state dispersion within <1 meV of the Fermi level. The technique is highly suitable for the pursuit of the topological magnetoelectric effect and axion electrodynamics.Comment: Published version, online Sept 23, 201

Spontaneous Vibrations and Stochastic Resonance of Short Oligomeric Springs

There is growing interest in molecular structures that exhibit dynamics similar to bistable mechanical systems. These structures have the potential to be used as nanodevices with two distinct states. Particularly intriguing are structures that display spontaneous vibrations and stochastic resonance. Previously, through molecular dynamics simulations, it was discovered that short pyridine-furan springs, when subjected to force loading, exhibit the bistable dynamics of a Duffing oscillator. In this study, we extend these simulations to include short pyridine-pyrrole and pyridine-furan springs in a hydrophobic solvent. Our findings demonstrate that these systems also display the bistable dynamics of a Duffing oscillator, accompanied by spontaneous vibrations and stochastic resonance activated by thermal noise.Comment: arXiv admin note: substantial text overlap with arXiv:2110.0409

High-Nuclearity (Cu₈‑Based) Cage Silsesquioxanes: Synthesis and Structural Study

We herein report a study of Cu­(II)-silsesquioxanes’ self-assembly in the presence of two possible template agents (acetonitrile and acetone). This results in the isolation of unusual high-nuclearity cluster Cu^II₈ cage silsesquioxanes [(Ph₈Si₈O₁₆)₂­Cu₈­(DMF)₈]­[Ph₈Si₈O₁₂]­·2MeCN <b>1</b> and [(Me₈Si₈O₁₆)₂­Cu₈­(Me₂CO)₄]₂­[MeCOO^–]₂­[Na⁺]₂­·2­(H₂O)­·3­(Me₂CO) <b>2</b>. In the case of <b>1</b>, acetonitrile indeed serves as a template being incorporated into the inner void of the prism-like cage of the crystalline product. To the contrary, in the case of complex <b>2</b>, acetone molecules just play the role of external solvates. An inner void of the prism-like cage in <b>2</b> is occupied by sodium acetate groups. The latter, most likely, are produced via the mild oxidation of ethanol during the synthesis of <b>2</b>. Finally, the sodium centers of these acetate groups caused an unprecedented “cage connectivity” (dimerization of two octacopper cage silsesquioxanes in <b>2</b>)

A New Mode of Operation of Pd-NHC Systems Studied in a Catalytic Mizoroki–Heck Reaction

Metal complexes bearing N-heterocyclic carbene (NHC) ligands are typically considered the system of choice for homogeneous catalysis with well-defined molecular active species due to their stable metal–ligand framework. A detailed study involving 19 different Pd-NHC complexes with imidazolium, benzimidazolium, and triazolium ligands has been carried out in the present work and revealed a new mode of operation of metal-NHC systems. The catalytic activity of the studied Pd-NHC systems is predominantly determined by the cleavage of the metal–NHC bond, while the catalyst performance is strongly affected by the stabilization of in situ formed metal clusters. In the present study, the formation of Pd nanoparticles was observed from a broad range of metal complexes with NHC ligands under standard Mizoroki–Heck reaction conditions. A mechanistic analysis revealed two different pathways to connect Pd-NHC complexes to “cocktail”-type catalysis: (i) reductive elimination from a Pd­(II) intermediate and the release of NHC-containing byproducts and (ii) dissociation of NHC ligands from Pd intermediates. Metal-NHC systems are ubiquitously applied in modern organic synthesis and catalysis, while the new mode of operation revealed in the present study guides catalyst design and opens a variety of novel opportunities. As shown by experimental studies and theoretical calculations, metal clusters and nanoparticles can be readily formed from M-NHC complexes after formation of new M–C or M–H bonds followed by C–NHC or H–NHC coupling. Thus, a combination of a classical molecular mode of operation and a novel cocktail-type mode of operation, described in the present study, may be anticipated as an intrinsic feature of M-NHC catalytic systems

Tridecanuclear Cu^II₁₁Na₂ Cagelike Silsesquioxanes

A series of three unprecedented heterometallic copper­(II) sodium silsesquioxanes were isolated (i) via the unusual rearrangement process during synthesis of coordination polymers or (ii) via the self-assembly reaction using 2,2′-bipyridine. The unique type of these products’ molecular topology consists of an unusual fusion of two sandwich-like components (each including five copper and one sodium sites) via a central copper ion. These compounds correspond to the highest nuclearity among Cu­(II)-based cage silsesquioxanes reported to date