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排序方式: 共有79条查询结果,搜索用时 31 毫秒
1.
Ernesto Carmona Jose M. Marin Manuel L. Poveda Robin D. Rogers Jerry L. Atwood 《Journal of organometallic chemistry》1982,238(4):C63-C66
The reduction of [WCl4(PMe3)3] with dispersed sodium, under dinitrogen, gives cis-[W(N2)2(PMe3)4], while under ethylene trans-[W(C2H4)2(PMe3)4] is obtained. The ethylene complex can also be prepared by displacement of the dinitrogen molecules in cis-[W(N2)2(PMe3)4] by ethylene at room temperature and pressure. Interaction of cis-[M(N2)2(PMe3)4] complexes (M = Mo, W), with PMe3, under helium or argon, yields [M(N2)(PMe3)5]. The molybdenum complex crystallizes in the orthorhombic space group Pnma, with a 22.063(6), b 12.106(4), c 9.745(4) Å. The Mo—P distance trans to the dinitrogen ligand (2.483(7) Å) is slightly longer than the average of the other four Mo—P bonds (2.460(5) Å). 相似文献
2.
A single-sheeted double many-body expansion (DMBE) potential energy surface is reported for the 1 2
A′′ state of NH2. To approximate its true multi-sheeted nature, a novel switching function that imposes the correct behavior at the H2(X 1Σ
g
+)+ N(2
D) and NH(X 3Σ-) + H(2
S) dissociation limits has been suggested. The new DMBE form is shown to fit with high accuracy an extensive set of new ab initio points (calculated at the multi-reference configuration interaction level using the full valence complete active space as reference and aug-cc-pVQZ and aug-cc-pV5Z basis sets) that have been semiempirically corrected at the valence regions by scaling the n-body dynamical correlation terms such as to account for the finite basis set size and truncated configuration interaction expansion. A detailed study of the N(2
D) ... H2(X 1Σ
g
+) van der Waals region has also been carried out. These calculations predict a nearly free rigid-rotor with two shallow van der Waals wells of C
2v
and C
∞ v
symmetries. Such a result contrasts with previous cc-pVTZ calculations which predict a single T-shaped van der Waals structure. Except in the vicinity of the crossing seam, which is replaced by an avoided intersection, the fit shows the correct physical behavior over the entire configurational space. The topographical features of the new DMBE potential energy surface are examined in detail and compared with those of other potential functions available in the literature. Amongst such features, we highlight the barrier for linearization (11,802 cm-1) which is found to overestimate the most recent empirical spectroscopic estimate by only 28 cm-1. Additionally, the T-shaped N(2
D) ... H2 van der Waals minimum is predicted to have a well depth of 90 cm-1, being 11 cm-1 deeper than the C
∞ v
minimum. The title DMBE form is therefore recommendable for dynamics studies of both non-reactive and reactive N(2
D)+H2 collisions. 相似文献
3.
Rocío Esquembre María Lourdes Renart Jos Antonio Poveda C. Reyes Mateo 《Molecules (Basel, Switzerland)》2022,27(19)
The nanostructuration of solid matrices with lipid nanoparticles containing membrane proteins is a promising tool for the development of high-throughput screening devices. Here, sol-gel silica-derived nanocomposites loaded with liposome-reconstituted KcsA, a prokaryotic potassium channel, have been synthesized. The conformational and functional stability of these lipid nanoparticles before and after sol-gel immobilization have been characterized by using dynamic light scattering, and steady-state and time-resolved fluorescence spectroscopy methods. The lipid-reconstituted KcsA channel entrapped in the sol-gel matrix retained the conformational and stability changes induced by the presence of blocking or permeant cations in the buffer (associated with the conformation of the selectivity filter) or by a drop in the pH (associated with the opening of the activation gate of the protein). Hence, these results indicate that this novel device has the potential to be used as a screening platform to test new modulating drugs of potassium channels. 相似文献
4.
M. Borlaf J. M. Poveda R. Moreno M. T. Colomer 《Journal of Sol-Gel Science and Technology》2012,63(3):408-415
Nanoparticulate TiO2/Rh3+ sols have been synthesized by the colloidal sol?Cgel route. The combination of the data measured with optical techniques such as laser diffraction, dynamic light scattering and multiple light scattering with a near-infrared light allows us to follow up the evolution of the peptization process and to establish the effect of the presence of Rh3+ on it. It is observed that the presence of rhodium ions retards the peptization step (t2) and decreases both the average particle size of the nanoparticles and the viscosity of the nanoparticulate sols. In addition, when Rh3+ is present the isoelectric point shifts up to higher pH, which suggests that chemical adsorption of the rhodium (III) cations onto the surface of the TiO2 nanoparticles is produced. The xerogels and cryogels obtained from the sols are constituted by anatase as major phase and traces of brookite. The phase transition is observed at lower temperatures for the xerogels containing rhodium (III) and at higher temperatures in the case of the cryogels. Finally, photocatalytic activity is higher in the case of the TiO2/Rh3+ sols due to the rhodium (III) effect on the electronic transitions from the valence band to the conduction band. 相似文献
5.
Dr. Luca Gabrielli Dr. Laura Russo Dr. Ana Poveda Dr. Julian R. Jones Prof. Francesco Nicotra Dr. Jesús Jiménez‐Barbero Prof. Laura Cipolla 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(24):7856-7864
Hybrid organic–inorganic solids represent an important class of engineering materials, usually prepared by sol–gel processes by cross‐reaction between organic and inorganic precursors. The choice of the two components and control of the reaction conditions (especially pH value) allow the synthesis of hybrid materials with novel properties and functionalities. 3‐Glycidoxypropyltrimethoxysilane (GPTMS) is one of the most commonly used organic silanes for hybrid‐material fabrication. Herein, the reactivity of GPTMS in water at different pH values (pH 2–11) was deeply investigated for the first time by solution‐state multinuclear NMR spectroscopic and mass spectrometric analysis. The extent of the different and competing reactions that take place as a function of the pH value was elucidated. The NMR spectroscopic and mass spectrometric data clearly indicate that the pH value determines the kinetics of epoxide hydrolysis versus silicon condensation. Under slighly acidic conditions, the epoxy‐ring hydrolysis is kinetically more favourable than the formation of the silica network. In contrast, under basic conditions, silicon condensation is the main reaction that takes place. Full characterisation of the formed intermediates was carried out by using NMR spectroscopic and mass spectrometric analysis. These results indicate that strict control of the pH values allows tuning of the reactivity of the organic and inorganic moities, thus laying the foundations for the design and synthesis of sol–gel hybrid biomaterials with tuneable properties. 相似文献
6.
Crispín Cristóbal Dr. Yohar A. Hernández Dr. Joaquín López‐Serrano Prof. Dr. Margarita Paneque Dr. Ana Petronilho Prof. Dr. Manuel L. Poveda Dr. Verónica Salazar Florencia Vattier Dr. Eleuterio Álvarez Dr. Celia Maya Prof. Dr. Ernesto Carmona 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(12):4003-4020
The reactivity of a series of iridium? pyridylidene complexes with the formula [TpMe2Ir(C6H5)2(C(CH)3C(R)N H] ( 1 a – 1 c ) towards a variety of substrates, from small molecules, such as H2, O2, carbon oxides, and formaldehyde, to alkenes and alkynes, is described. Most of the observed reactivity is best explained by invoking 16 e? unsaturated [TpMe2Ir(phenyl)(pyridyl)] intermediates, which behave as internal frustrated Lewis pairs (FLPs). H2 is heterolytically split to give hydride? pyridylidene complexes, whilst CO, CO2, and H2C?O provide carbonyl, carbonate, and alkoxide species, respectively. Ethylene and propene form five‐membered metallacycles with an IrCH2CH(R)N (R=H, Me) motif, whereas, in contrast, acetylene affords four‐membered iridacycles with the IrC(?CH2)N moiety. C6H5(C?O)H and C6H5C?CH react with formation of Ir? C6H5 and Ir? C?CPh bonds and the concomitant elimination of a molecule of pyridine and benzene, respectively. Finally the reactivity of compounds 1 a – 1 c against O2 is described. Density functional theory calculations that provide theoretical support for these experimental observations are also reported. 相似文献
7.
Experimental and Theoretical Studies on Arene‐Bridged Metal–Metal‐Bonded Dimolybdenum Complexes
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Dr. Mario Carrasco Natalia Curado Dr. Eleuterio Álvarez Dr. Celia Maya Dr. Riccardo Peloso Prof. Dr. Manuel L. Poveda Dr. Amor Rodríguez Prof. Dr. Eliseo Ruiz Prof. Dr. Santiago Álvarez Prof. Dr. Ernesto Carmona 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(20):6092-6102
The bis(hydride) dimolybdenum complex, [Mo2(H)2{HC(N‐2,6‐iPr2C6H3)2}2(thf)2], 2 , which possesses a quadruply bonded Mo2II core, undergoes light‐induced (365 nm) reductive elimination of H2 and arene coordination in benzene and toluene solutions, with formation of the MoI2 complexes [Mo2{HC(N‐2,6‐iPr2C6H3)2}2(arene)], 3?C6H6 and 3?C6H5Me , respectively. The analogous C6H5OMe, p‐C6H4Me2, C6H5F, and p‐C6H4F2 derivatives have also been prepared by thermal or photochemical methods, which nevertheless employ different Mo2 complex precursors. X‐ray crystallography and solution NMR studies demonstrate that the molecule of the arene bridges the molybdenum atoms of the MoI2 core, coordinating to each in an η2 fashion. In solution, the arene rotates fast on the NMR timescale around the Mo2‐arene axis. For the substituted aromatic hydrocarbons, the NMR data are consistent with the existence of a major rotamer in which the metal atoms are coordinated to the more electron‐rich C?C bonds. 相似文献
8.
9.
10.
N. A. Borisevich V. A. Povedaĭlo V. A. Tolkachev D. L. Yakovlev 《Optics and Spectroscopy》2006,101(2):199-205
The fluorescence and fluorescence excitation spectra of jet-cooled dinaphtho[2,1-b:1′,2′-d]furan (dinaphthofuran) molecules, as well as their complexation with inert gases Ar, Kr, and Xe, are studied. The indicatrices of the degree of polarization of fluorescence of dinaphthofuran molecules upon excitation of the electronic transitions S 0?S 1 and S 0?S 2 are calculated as functions of the intramolecular orientation of the transition dipole moments. The fluorescence polarization spectrum is measured under excitation within the rotational contour of the line of the purely electronic transition v 0 0 = 29 294 cm?1. In contrast to complex planar molecules, the S 0?S 2 fluorescence excitation spectrum of dinaphthofuran is found to be continuous, with the Q branch of the rotational contour being absent. The fluorescence excitation spectra of van der Waals complexes of dinaphthofuran with inert gases exhibit multiplet lines, which is associated with the helical structure of the molecules studied. 相似文献