Search results for "Note"
showing 10 items of 10709 documents
Magnetic properties of vanadium(IV)-based extended systems: [(VO)3(μ-PO4)2(2,2′-bpy)(μ-OH2)]*1/3H2O and (VO)2H4P2O9
2013
International audience; The magnetic properties of [(VO)3(μ-PO4)2(2,2′-bpy)(μ-OH2)]1/3H2O (1) and (VO)2H4P2O9 (2), a tubular and a layered vanadium(IV) phosphates containing triply oxido bridged VIV dimers, are analyzed considering the Bleaney-Bowers S = 1/2 dimer model. In compound 1 the presence of an additional VIV connected with the VIV dimers through μ1,2-PO43− bridges is described with a Curie-Weiss type correction. This model reproduces the magnetic properties of compound 1 with g = 1.956, Jdim = −102.1 cm−1, θ = −0.4 cm−1 and Nα = 278 × 10−6 emu mol−1. In compound 2, the presence of a small percentage of paramagnetic impurity has to be considered to account for the divergence of χm …
Electronic structure and energy decomposition analyses as a tool to interpret the redox potential ranking of naphtho-, biphenyl- and biphenylenequino…
2016
By calling on modelling approaches we have performed a comparative study on the redox properties of various naphtho-, biphenyl- and biphenylene-quinone isomers. These different compounds exhibit as a whole a redox potential range between 2.09 and 2.90 V vs. Li+/Li. A specific methodology was used to decrypt the interplay among isomerism, aromaticity and antiaromaticity modifications and the stabilization/destabilization effects due to other molecular components on this key electrochemical feature for electrode materials of batteries. In particular, energy decomposition analysis, within the Quantum Theory of Atoms in Molecules, along with the electron and electron spin population changes upo…
Potassium Triggers a Reversible Specific Stiffness Transition of Polyethylene Glycol
2017
We use plasmon rulers made from two connected gold nanoparticles to monitor the conformation and stiffness of single PEG molecules and their response to cations. By observing equilibrium fluctuations of the interparticle distance, we obtain the spring constants or stiffness of the connecting single-molecule tether with pico-Newton sensitivity. We observe a transition of the PEG molecules’ extension and stiffness above about 1.2 mM K+ ion concentration which is specific to potassium ions. Molecular dynamics simulations reveal the formation of crown-like structures as the most likely molecular mechanism responsible for this specific effect.
Bulky Surface Ligands Promote Surface Reactivities of [Ag141X12(S-Adm)40]3+ (X = Cl, Br, I) Nanoclusters: Models for Multiple-Twinned Nanoparticles
2017
Surface ligands play important roles in controlling the size and shape of metal nanoparticles and their surface properties. In this work, we demonstrate that the use of bulky thiolate ligands, along with halides, as the surface capping agent promotes the formation of plasmonic multiple-twinned Ag nanoparticles with high surface reactivities. The title nanocluster [Ag141X12(S-Adm)40]3+ (where X = Cl, Br, I; S-Adm = 1-adamantanethiolate) has a multiple-shell structure with an Ag71 core protected by a shell of Ag70X12(S-Adm)40. The Ag71 core can be considered as 20 frequency-two Ag10 tetrahedra fused together with a dislocation that resembles multiple-twinning in nanoparticles. The nanocluster…
A stereotactic device for rabbits based on mandibular and cranial landmarks
2008
✓ The authors have developed a stereotactic device for use in rabbits that uses the plane at the base of the mandible combined with cranial sutures as an anatomical reference. The device was developed for a study designed to evaluate catheters for infection prophylaxis, and this required the implantation of silicone catheters along a reproducible trajectory through the lateral ventricle. Cadaver and atlas studies demonstrated consistent spatial relationships between intracranial structures and the surface plane on which the animals were resting during the surgery. This plane is formed by the 2 mandibular angles and the mandibular tip. The authors developed a stainless steel stereotactic dev…
Exploration of the Solid-State Sorption Properties of Shape-Persistent Macrocyclic Nanocarbons as Bulk Materials and Small Aggregates.
2020
Porous molecular materials combine benefits such as convenient processability and the possibility for atom-precise structural fine-tuning which makes them remarkable candidates for specialty applications in the areas of gas separation, catalysis, and sensing. In order to realize the full potential of these materials and guide future molecular design, knowledge of the transition from molecular properties into materials behavior is essential. In this work, the class of compounds termed cycloparaphenylenes (CPPs)-shape-persistent macrocycles with built-in cavities and radially oriented π-systems-was selected as a conceptually simple class of intrinsically porous nanocarbons to serve as a platf…
Overcoming Steric Hindrance in Aryl‐Aryl Homocoupling via On‐Surface Copolymerization
2019
On-surface synthesis is a unique tool for growing low-dimensional carbon nanomaterials with precise structural control down to the atomic level. This novel approach relies on carefully designed precursor molecules, which are deposited on suitable substrates and activated to ultimately form the desired nanostructures. One of the most applied reactions to covalently interlink molecular precursors is dehalogenative aryl-aryl coupling. Despite the versatility of this approach, many unsuccessful attempts are also known, most of them associated to the poor capability of the activated precursors to couple to each other. Such failure is often related to the steric hindrance between reactants, which…
Solid State Luminescence Enhancement in π-Conjugated Materials: Unraveling the Mechanism beyond the Framework of AIE/AIEE
2017
Solid state luminescence enhancement (SLE) of conjugated organic materials has had a great impact in materials science, but a deep understanding has been rather limited to date. Here, we investigate a prototype example of SLE materials, cyano-substituted distyrylbenzene (DCS), by varying systematically and subtly the substitution pattern (inter alia of the position of the cyano-substituent) to give largely different photoresponse in fluid and solid solution as well in the crystalline state. The combination of quantitative (ultra)fast optical spectroscopic techniques, appropriate quantum-chemical methods, and structural (X-ray) data allows us to elucidate and rationalize all details of the S…
Thermotropic properties and molecular packing of discotic tristriazolotriazines with rigid substituents.
2014
Tristriazolotriazines with a threefold dialkoxyaryl substitution have been prepared by Huisgen reaction of cyanuric chloride and the corresponding tetrazoles. Although these dyes show a negative or inverted solvatochromism of the UV/Vis absorption, their fluorescence is strongly positive solvatochromic. These discotic fluorophores are also emissive in their solid state and in their broad liquid-crystalline mesophase. The structural study indicates that the thermotropic properties and organization of these systems can be well tuned by the steric demand of the aryl groups. Depending on the substituents, the compounds showed either a pure crystalline phase or a highly complex helical superstru…
Flipping Motion To Bias the Organized Supramolecular Polymerization of N-Heterotriangulenes
2019
Synergistic experimental and theoretical studies have allowed the disentangling of the possible pathways for the supramolecular polymerization of a series of dicyanovinyl-bridged N-heterotriangulene (NHT) derivatives bearing benzamide units with achiral (1a) and chiral (1b,c) side chains. The synthesis of these bowl-shaped, self-assembling units yields a mixture of monomeric species with C3- and C1-symmetry. Both monomeric species are able to self-assemble into different supramolecular aggregates with sufficient stability to coexist in freshly prepared solutions. The dissimilar ratio of the aggregates initially generated results in different spectroscopic features and, more specifically, in…