7 research outputs found
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 (Cu<sub>8</sub>‑Based) Cage Silsesquioxanes: Synthesis and Structural Study
We
herein report a study of CuÂ(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<sup>II</sup><sub>8</sub> cage silsesquioxanes [(Ph<sub>8</sub>Si<sub>8</sub>O<sub>16</sub>)<sub>2</sub>ÂCu<sub>8</sub>Â(DMF)<sub>8</sub>]Â[Ph<sub>8</sub>Si<sub>8</sub>O<sub>12</sub>]·2MeCN <b>1</b> and [(Me<sub>8</sub>Si<sub>8</sub>O<sub>16</sub>)<sub>2</sub>ÂCu<sub>8</sub>Â(Me<sub>2</sub>CO)<sub>4</sub>]<sub>2</sub>Â[MeCOO<sup>–</sup>]<sub>2</sub>Â[Na<sup>+</sup>]<sub>2</sub>·2Â(H<sub>2</sub>O)·3Â(Me<sub>2</sub>CO) <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 PdÂ(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<sup>II</sup><sub>11</sub>Na<sub>2</sub> Cagelike Silsesquioxanes
A series
of three unprecedented heterometallic copperÂ(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 CuÂ(II)-based cage silsesquioxanes reported to date