Bowl-shaped Structure Research Articles

ChemInform Abstract: Structurally‐Modified Subphthalocyanines: Molecular Design Towards Realization of Expected Properties from the Electronic Structure and Structural Features of Subphthalocyanine

AbstractReview: [73 refs.

First Nest Record of Red-throated Caracara (Ibycter americanus) for Middle America

Abstract Populations of Red-throated Caracaras (Ibycter americanus) have been extirpated or are in serious decline throughout Middle America. We describe the first nest outside South America and provide only the third nest description for the species. We observed four adults and one immature Red-throated Caracara provide cooperative care to a single nestling at a nest in a region dominated by pine-oak forest in departamento (dpto.) de Olancho, Honduras. The nest was a bowl-shaped structure of branches and pine needles located at the mid-canopy level of a pine tree (Pinus oocarpa), and is the first nest described in an ecosystem other than humid broadleaf forest. We report the first observation of adult Red-throated Caracaras using a nest as a short-term food cache, as well as the first observation of Red-throated Caracara taking fledgling birds as prey. Although Red-throated Caracaras are considered a resident of humid broadleaf forest, we suggest that pine-oak forests may be an important habitat for the ...

A Core‐Expanded Subphthalocyanine Analogue with a Significantly Distorted Conjugated Surface and Unprecedented Properties

The introduction of a seven-membered-ring unit in the place of a five-membered-ring unit in the structure of subphthalocyanine resulted in significant distortion of the bowl-shaped structure of the conjugated molecule as well as the following unprecedented properties: the preferential formation of the axially fluoro substituted species, the fluttering-dynamic-motion-induced rapid exchange of P and M enantiomers, markedly split Q-band absorption, and a clear difference in the ring-current effects arising from the convex and concave surfaces.

Constraint-induced structural deformation of planarized triphenylboranes in the excited state

Triphenylboranes planarized with three methylene bridges exhibited dual fluorescence bands around 340 and 400 nm despite their structural constraint. To elucidate the origin, their excited state dynamics were experimentally and theoretically studied. The measurements of fluorescence lifetimes and transient absorption spectra indicated that the planarized triphenylboranes adopt two local minimum structures in the lowest-energy excited singlet (S1) state. The TD-DFT potential energy surface of the S1 state possesses at least two minimum energy structures associated with a planar and a bowl-shaped molecular structure. The theoretical S1–S0 transition energies at these geometries were in good agreement with the experimentally observed values. These results indicated that the plane-to-bowl structural relaxation in the S1 state is the origin of the dual fluorescence. Based on the calculated partial atomic charge on the boron atom, the structural deformation to the bowl-shaped structure results in an increase in the electron density on the boron center. Thus, the enhanced intramolecular charge-transfer character plays a role in this structural deformation. Similar behavior was also observed for trigonally π-expanded planarized borane derivatives. These results provide an important implication that structural constraint in a planar fashion is not only a strategy to construct a rigid skeleton, but also a viable mechanism to impart flexibility to the skeleton.

A bowl-shaped molecule for organic field-effect transistors: crystal engineering and charge transport switching by oxygen doping

A corannulene-based derivative was facilely developed with a bowl-shaped structure. Highly ordered cofacial convex–concave stacking was realized through tuning the molecular dipoles, which is favorable for charge transport. Organic field-effect transistors were fabricated, providing opportunities for a broad class of corannulene derivatives and buckybowl aromatics for application in future organic electronic devices.

Scalable Virtual-Ground Multilevel-Cell Floating-Gate Flash Memory

An adequate gate coupling ratio (GCR) and compensation for floating-gate to floating-gate (FG-to-FG) coupling interference must be maintained to enable further scaling of virtual-ground multilevel-cell (MLC) FG flash memory. A high GCR of 0.6 is obtained using a novel bowl-shaped FG structure cell technology without sacrificing cell size. Increasing the GCR is important for reducing FG-to-FG coupling interference and achieving low-voltage operation. A novel array segmented virtual-ground architecture with bit-line isolation between neighboring segments and two-step programming with the channel hot electron injection threshold voltage compensation technique are proposed to reduce the number of neighboring cells that are programmed after programming a given cell, as well as the amount of threshold voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> ) shift of the neighboring cells. Adoption of this programming approach realizes a reduction in the V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> shift caused by the FG-to-FG coupling interference in the bit-line direction, compared with conventional programming approaches, and the V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> shift is almost completely eliminated in the word-line direction without sacrificing program throughput. The proposed virtual-ground MLC FG cell, which is as small as 3F <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /bit ( F is the minimum feature size) is successfully implemented into a test chip with good reliability.

Investigation of the Abrasive Removal Depth for Bowl-Shaped Structure of Sapphire Wafer Under Compensated Chemical Mechanical Polishing

Investigation of the Abrasive Removal Depth for Bowl-Shaped Structure of Sapphire Wafer Under Compensated Chemical Mechanical Polishing

Controlling sol–gel polymerization to create bowl-shaped polysilsesquioxane particles with a kippah structure

Bowl-shaped particles in sub-micrometer scale represent an interesting platform for many potential applications. However, controlled fabrication of this special structure based on polymers still remains a big challenge. In the present study, a controllable sol–gel polymerization procedure was developed to precisely prepare bowl-shaped polysilsesquioxane particles. The morphology of particles can be fine-tuned by judiciously adjusting the amount of two organoalkoxysilane precursors. We explored the formation mechanism of bowl-shaped polysilsesquioxane particles with a kippah structure. The flexibility of the shell and osmotic pressure in combination with centrifugal force should be the key factors to the formation of a bowl-shaped structure.

High-resolution reflection seismic investigations of quick-clay and associated formations at a landslide scar in southwest Sweden

We present high-resolution reflection seismic data from four lines (total 1.9 km) that cross a quick-clay landslide scar located close to the shore of the Göta River in southwest Sweden, and compare the results with geotechnical data from boreholes. The seismic data allow the imaging of bedrock topography and normally to weakly consolidated sediments to a subsurface depth of about 100 m. Different types of seismic sources, including sledgehammer, accelerated weight-drop and dynamite were utilized and compared with each other. Analysis of their power spectra suggests that weight-drop and dynamite have higher frequency content and energy than the sledgehammer, which makes these two sources suitable also for waveform tomography and surface-wave data analysis. The shallowest non-bedrock reflector is observed at about 10–20 m below the surface, it overlays the bedrock, and is interpreted to originate from the contact between clay formations above and a coarse-grained layer below. The coarse-grained layer appears to be spatially linked to the presence of quick-clays. It is a regional scale formation, laterally heterogeneous, which deepens to the west of the study area and correlates well with the available geotechnical data. Continuity of the coarse-grained layer becomes obscured by the landslide scar. There may be a link between the coarse-grained layer and landslides in the study area, although this possibility requires further hydrogeological and geotechnical investigations. Reflectors from the top of the bedrock suggest a depression zone with its deepest point below the landslide scar and a bowl-shaped structure in the northern portion of one of the seismic lines.

Synthesis and STM Imaging of Symmetric and Dissymmetric Ethynyl‐Bridged Dimers of Boron–Subphthalocyanine Bowl‐Shaped Nanowheels

The future's wheel: A new class of wheels, based on subphthalocyanine fragments, for future incorporation in functional nanovehicles is reported (see figure). The syntheses of a symmetric wheel, a nitrogen-tagged wheel, and their ethynyl-bridged homodimers are presented. Theoretical calculations and STM imaging demonstrate the advantage of a bowl-shaped structure and the efficiency of the tag for STM imaging.

Effects of acoustic-streaming-induced flow in evaporating nanofluid droplets

AbstractWe study the effect of acoustic streaming on nanoparticle motion and morphological evolution inside an acoustically levitated droplet using an analytical approach coupled with experiments. Nanoparticle migration due to internal recirculation forms a density stratification, the location of which depends on initial particle concentration. The time scale of density stratification is similar to that of perikinetic-driven agglomeration of particle flocculation. The density stratification ultimately leads to force imbalance leading to a unique bowl-shaped structure. Our analysis shows the mechanism of bowl formation and how it is affected by particle size, concentration, internal recirculation and fluid viscosity.

Synthesis and C2-symmetric structure of a cyclotetrapeptide composed of anthranilic acid and leucine

A chiral cyclotetrapeptide (1) was synthesized from 2-nitrobenzoic acid and leucine. A single-crystal X-ray of the compound revealed a C(2) -symmetric bowl-shaped structure. The cyclic compound had a unique hydrogen-bonding network composed of three-centered hydrogen bonds and bifurcated hydrogen bonds between NH and CO of anthranilic residue. The NMR spectra and molecular modeling of 1 also suggested the chiral bowl structure.

A Mn(iii)–superoxo complex of a zwitterionic calix[4]arene with an unprecedented linear end-on Mn(iii)–O2 arrangement and good catalytic performance for alkene epoxidation

Reactions of [H(4)L][PF(6)](4) with 4 equiv. of Mn(OAc)(2)·4H(2)O in the presence of air gave rise to a mononuclear Mn(III)-superoxo complex [Mn(III)L(O(2))(H(2)O)](PF(6))(2), which contains a bowl-shaped cationic structure with a D(4d) symmetry. It has an unprecedented linear end-on Mn(III)-O(2) unit and exhibited good efficiency and selectivity in the catalytic oxidation of alkenes with O(2) plus isobutyraldehyde under mild conditions.

Rational design of single-molecule magnets: a supramolecular approach

Since the discovery that Mn(12)OAc acts as a single-molecule magnet (SMM), an increasing number of transition metal complexes have been demonstrated to behave as SMMs. The signature of a SMM is a slow relaxation of the magnetization at low temperatures accompanied by a magnetic hysteresis. The origin of SMM behaviour is the existence of an appreciable thermal barrier U for spin-reversal called magnetic anisotropy barrier which is related to the combination of a large total spin ground state (S(t)) and an easy-axis magnetic anisotropy. The extensive research on Mn(12)OAc and other SMMs has established more prerequisites for a rational development of new SMMs besides the high-spin ground state and the magnetic anisotropy: the symmetry should be at least C(3) to minimize the quantum tunneling of the magnetization through the anisotropy barrier but lower than cubic to avoid the cancellation of the local anisotropies upon projection onto the spin ground state. Based on these prerequisites, we have designed the ligand triplesalen which combines the phloroglucinol bridging unit for high spin ground states by the spin-polarization mechanism with a salen-like ligand environment for single-site magnetic anisotropies by a strong tetragonal ligand field. The C(3) symmetric, trinuclear complexes of the triplesalen ligand (talen(t-Bu(2)))(6-) exhibit a strong ligand folding resulting in an overall bowl-shaped molecular structure. This ligand folding preorganizes the axial coordination sites of the metal salen subunits for the complementary binding of three facial nitrogen atoms of a hexacyanometallate unit. This leads to a high driving force for the formation of heptanuclear complexes [M(t)(6)M(c)](n+) by the assembly of three molecular building blocks. Attractive van der Waals interactions of the tert-butyl phenyl units of two triplesalen trinuclear building blocks increase the driving force. In this respect, we have been able to synthesize the isostructural series [Mn(III)(6)Cr(III)](3+), [Mn(III)(6)Fe(III)](3+), and [Mn(III)(6)Co(III)](3+) with [Mn(III)(6)Cr(III)](3+) being a SMM. A detailed analysis and comparison of the magnetic properties of the three heptanuclear complexes and the tetranuclear half-unit [Mn(III)(3)Cr(III)](3+) provides significant insight for further optimization of the SMM properties. The modular assembly of the heptanuclear complexes from three molecular building blocks allows the fine-tuning of the molecular and steric properties of each building block without losing the driving force for the formation of the heptanuclear complexes. This possibility of rational improvements of our isostructural series is the main advantage of our supramolecular approach.

Bromido(dodecafluorosubphthalocyaninato)boron(III)

The title compound, C24BBrF12N6 or Br-F12BsubPc (BsubPc is boronsubphtalocyanine), has a bowl-shaped structure with an approximate mol­ecular C 3v symmetry characteristic of boronsubphthalocyanine compounds. In the crystal, mol­ecules are arranged in one-dimensional columns and the boron–subphthalocyanine units within each column are offset and angled in a bowl-to-ligand packing arrangement such that the axial Br atom rests in the aromatic concaved bowl of the neighboring subphthalocyanine with an inter­molecular Br⋯B distance of 3.721 (3) Å.

ChemInform Abstract: Structure and Stability of the Heteroannulated [8‐10]Circulenes: A Quantum‐Chemical Study

AbstractReview: 41 refs.

A novel method for generation of amphiphilic PDMS particles by selective modification

We reported a novel method to fabricate both spherical and nonspherical PDMS (Polydimethylsiloxane) particles of amphiphilic property. PDMS particles were first obtained using microfluidic devices. A layer of PAA (poly (acrylic acid)) polymer was then selectively grafted on a section of particle surface. After modification, PDMS particles exhibited an amphiphilic property. We demonstrated the assembly of spherical particles at the water/oil interface as well as the deformation of cuboidal particles which possessed a bowl-shaped structure after deformation.

Direct transformation of graphene to fullerene

Although fullerenes can be efficiently generated from graphite in high yield, the route to the formation of these symmetrical and aesthetically pleasing carbon cages from a flat graphene sheet remains a mystery. The most widely accepted mechanisms postulate that the graphene structure dissociates to very small clusters of carbon atoms such as C(2), which subsequently coalesce to form fullerene cages through a series of intermediates. In this Article, aberration-corrected transmission electron microscopy directly visualizes, in real time, a process of fullerene formation from a graphene sheet. Quantum chemical modelling explains four critical steps in a top-down mechanism of fullerene formation: (i) loss of carbon atoms at the edge of graphene, leading to (ii) the formation of pentagons, which (iii) triggers the curving of graphene into a bowl-shaped structure and which (iv) subsequently zips up its open edges to form a closed fullerene structure.

Structure and stability of the heteroannulated [8–10]circulenes: A quantum-chemical study

The structure and stability of a new family of heterocyclic [n]circulenes CnNnYn (n = 8–10; Y = N, P, As, BF2, AlF2, GaF2) have been computationally studied using density functional theory (DFT) B3LYP/6-311G* calculations. The geometry of the compounds is determined by the balance of steric factors and effects of aromatic π-electron delocalization depending on the electronegativity of heteroatoms. An increase in the bulkiness of peripheral atoms Y and enlargement of the inner Cn cycle leads to the gradual transformation of the bowl-shaped circulene structure (Y = N, BF2) to planar and then saddle-shaped forms (Y = P, As, AlF2, GaF2). The calculations performed manifest stabilization of the heteroannulated circulenes ensured by the strong aromatic character of the conjugated five-membered rings fringing the central non-aromatic or antiaromatic [8–10] annulene rings.

Tuning the reactivity of chelated dinuclear Pt(ii) complexes through a flexible diamine linker. A detailed kinetic and mechanistic study

The rate of displacement of the aqua ligands by three neutral nucleophiles (Nu) of different steric demands, namely thiourea (tu), N,N'-dimethylthiourea (dmtu) and N,N,N',N'-tetramethylthiourea (tmtu) and an anionic nucleophile (I(-)) in complexes of the form [{Pt(H(2)O)}(2)(N,N,N',N'-tetrakis(2-pyridylmethyl)-N(CH(2))(n)N](CF(3)SO(3))(4), n = 2 (En); 3 (Prop); 4 (But); 6 (Hex); 8 (Oct) and 10 (Dec), was studied under pseudo first-order conditions as a function of concentration, temperature and pressure using stopped-flow techniques and UV-visible spectrophotometry. The pseudo first-order rate constants, k(obs(1(st)/2(nd))), for the simultaneous substitution of the aqua ligands and the proposed subsequent dechelation of the pyridyl units, respectively, agreed well to the rate law: k(obs(1(st)/2(nd))) = k(2(1(st)/2(nd)))[Nu]. High negative activation entropies, negative volumes of activation and second-order kinetics for the displacement reactions all support an associative mode of activation. Except for Prop, the rate of the simultaneous substitution of the aqua ligands in the complexes was found to increase as the chain length of the linker increases from En to Hex, beyond which any further increase in chain length is not accompanied by a further increase in reactivity. The reactivity trend of the even-bridged complexes with C(2h) symmetry is ascribed to a concomitant decrease in axial steric influences imposed on one side of the square-planar picolyl chelates by the other as the chain length increases. Based on the model structures of the complexes, this kind of steric imposition occurs only in complexes with an even number of CH(2) groups within the linker. The Prop complex, having a C(2v) symmetry showed exceptional high reactivity towards the nucleophiles. A cage effect, evolving from its bowl-shaped molecular structure, is proposed to explain this high reactivity. The order of reactivity of the nucleophiles increased in the order I(-) >> tu approximately dmtu > tmtu, in line with the strong electrostatic interactions between the highly polarizable iodide nucleophile and the Pt centers, steric retardation effects in the case of tmtu and dominating positive inductive effects for the dmtu nucleophile.