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21.
22.
H.C. Clark S.S. McBride N.C. Payne C.S. Wong 《Journal of organometallic chemistry》1979,178(2):393-408
The reaction of [Pt((F3C)CCH(CF3))(P(C2H5)3)2CH3OH]PF6 with allene in methanol affords a novel metallocyclic ethereal complex [CH3)(P(C2H5)3)2]PF6, which has been characterized by 1H, 2H, 19F and 31P NMR spectroscopy. Its structure has also been determined by a single crystal X-ray analysis. The crystal are monoclinic, space group P21/n, with cell dimensions a 20.012(5), b 17.222(5), c 8.902(3) Å and β 91.54(5)°. The structure was refined by full matrix least-squares methods on F, using 3097 unique observations collected by automated four circle diffractometer. Refinement converged at R 0.066. The Pt atom has a distorted square-planar coordination geometry, with cis P atoms, and PtP distances of 2.219(4) Å (trans to O) and 2.324(4) Å (trans to C). These results show the ethereal group is a weak ligand to platinum(II) but because of the chelating effect, its displacement by other ligands is thermodynamically not favorable. The mechanism of formation of the ethereal complex is also discussed. 相似文献
23.
Ab initio total energy calculations have been performed for CO chemisorption on Pd{110}. Local density approximation (LDA) calculations yield chemisorption energies which are significantly higher than experimental values but inclusion of the generalised gradient approximation (GGA) gives better agreement. In general, sites with higher coordination of the adsorbate to surface atoms lead to a larger degree of overbinding with LDA, and give larger corrections with GGA. The reason is discussed using a first-order perturbation approximation. It is concluded that this may be a general failure of LDA for chemisorption energy calculations. This conclusion may be extended to many surface calculations, such as potential energy surfaces for diffusion. 相似文献
24.
Holder Alvin A. Brown Ross F. G. Marshall Sophia C. Payne Vince C. R. Cozier Maria D. Alleyne Walter A. Bovell Christopher O. 《Transition Metal Chemistry》2000,25(5):605-611
A detailed investigation of the oxidation of L-ascorbic acid (H2A) by the title complex has been carried out using conventional spectrophotometry at 510 nm, over the ranges: 0.010 [ascorbate]
T
0.045 mol dm–3, 3.62 pH 5.34, and 12.0 30.0 °C, 0.50 I 1.00 mol dm–3, and at ionic strength 0.60 mol dm–3 (NaClO4). The main reaction products are the bis(pyridine-2,6-dicarboxylate)cobaltate(II) ion and l-dehydroascorbic acid. The reaction rate is dependent on pH and the total ascorbate concentration in a complex manner, i.e., k
obs = (k
1
K
1)[ascorbate]
T
/(K
1 + [H+]). The second order rate constant, k
1 [rate constant for the reaction of the cobalt(III) complex and HA–] at 25.0 °C is 2.31 ± 0.13 mol–1 dm3 s–1. H
= 30 ± 4 kJ mol–1 and S
= –138 ± 13 J mol–1 K–1. K
1, the dissociation constant for H2A, was determined as 1.58 × 10–4 mol dm–3 at an ionic strength of 0.60 mol dm–3, while the self exchange rate constant, k
11 for the title complex, was determined as 1.28 × 10–5 dm3 mol–1 s–1. An outer-sphere electron transfer mechanism has been proposed. 相似文献
25.
One-atom detection techniques have been used to test the equality between time and ensemble averages, following a gedanken experiment on the diffusion of atoms suggested by Einstein and Fürth. Experimental results confirmed that a system of freely diffusing atoms was ergodic. 相似文献
26.
Wu LQ Lee K Wang X English DS Losert W Payne GF 《Langmuir : the ACS journal of surfaces and colloids》2005,21(8):3641-3646
Nanoscale particles offer a variety of interesting properties, and there is growing interest in their assembly into higher ordered structures. We report that the pH-responsive aminopolysaccharide chitosan can mediate the electrodeposition of model nanoparticles. Chitosan is known to electrodeposit at the cathode surface in response to a high localized pH. To demonstrate that chitosan can mediate nanoparticle deposition, we suspended fluorescently labeled latex nanoparticles (100 nm diameter spheres) in a chitosan solution (1%) and performed electrodeposition (0.05 mA/cm2 for several minutes). Results demonstrate that chitosan is required for nanoparticle electrodeposition; chitosan confers spatial selectivity to electrodeposition; and nanoparticles distribute throughout the electrodeposited chitosan film. Additionally, we observed that the deposited films reversibly swell upon rehydration. This work indicates that chitosan provides a simple means to assemble nanoparticles at addressable locations and provides further evidence that stimuli-responsive biological materials may facilitate fabrication at the microscale. 相似文献
27.
Stuart Lang Neil Muir Franziska Schönebeck Andrew H. Payne 《Tetrahedron letters》2005,46(23):4027-4030
The phosphorus based radical precursors N-ethylpiperidine hypophosphite (EPHP) and diethylphosphine oxide (DEPO) are efficient reagents for carrying out the formation of seven- and eight-membered rings. Esters and amides were successfully converted into the corresponding eight-membered lactones and seven- and eight-membered lactams in good to excellent yields. 相似文献
28.
L. E. Payne G. A. Philippin 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1991,42(6):864-873
Summary In this paper we study various overdetermined problems involving harmonic functions. In particular, we show that if the second eigenfunctionu
2 of the Stekloff eigenvalue problem in a bounded simply connected plane domain has a constant value of u
2 on , then is a disk
Résumé Cet article est consacré à l'étude de certains problèmes surdéterminés pour des fonctions harmoniques. En particulier, nous montrons que si le gradient de la seconde fonction propre du problème de Stekloff défini dans un domaine borné, simplement connexe du plan, a son module constant sur la frontière , alors est nécessairement un disque.相似文献
29.
30.