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排序方式: 共有165条查询结果,搜索用时 15 毫秒
1.
In an extension of studies of flameless atomizers for atomic-absorption spectrometry, an electrically heated tungsten-rhenium alloy wire loop was examined. Reduction of metallic salts to ground-state metal atoms was accomplished with the high temperature produced by the loop. Lead and nickel were investigated. Experimental parameters such as wavelength, slit width, atomization temperature and sheathing gas flow rate were optimized. Absolute detection limits of 6.6·10?10 and 1.2·10?10, and absolute sensitivities of 7·10?10 and 8·10?11 g of lead, were established for unenclosed and enclosed cells, respectively. The interferences of twenty cations and sixteen anions were studied; foreign cations generally enhanced the lead absorption by retarding its vaporization, allowing the slow detection system to respond more efficiently. Nickel was investigated as a representative less volatile metal; an absolute detection limit of 1.6·10?9 and an absolute sensitivity of 9·10?10 g of nickel were established. 相似文献
2.
Bibal C Santini CC Chauvin Y Vallée C Olivier-Bourbigou H 《Dalton transactions (Cambridge, England : 2003)》2008,(21):2866-2870
A new family of hydroxytris(pentafluorophenyl)borate anions [B(C6F5)3OH](-) associated with organic and aprotic cations c+ (imidazolium, pyrrolidinium and phosphonium) has been prepared by a general one-pot synthesis that implies the chloride borate analogues [B(C6F5)3Cl](-)[c]+. The [c]+[B(C6F5)3OH](-) salts have been isolated and fully characterized. The borate anion [B(C6F5)3OH](-) has been shown to protonate the Zr-Me bond in the Cp2ZrMe2 complex forming CH4 and the first published example of anionic [Cp2Zr(Me)OB(C6F5)3](-) species. Standard spectroscopic methods demonstrate the covalent character of the Zr metal center and the anionic character of the boron atom. This protonolysis methodology using [B(C6F5)3OH](-) anion affords a new route for the incorporation of a covalently bonded anionic functionality on organometallic complexes. This provides a new way to immobilize transition metal complexes in ionic liquids. 相似文献
3.
Chauvin J Lafolet F Chardon-Noblat S Deronzier A Jakonen M Haukka M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(15):4313-4322
Optical excitation in the visible region of trans-(Cl)-[Os(bpy)(CO)(2)Cl(2)] (bpy=2,2'-bipyridine; C1) and trans-(Cl)-[Os(dmbpy)(CO)(2)Cl(2)] (dmbpy=4,4'-dimethyl 2,2'-bipyridine; C2) is known to induce the common CO dissociation reaction. However, the quantum yield of the reactions is less than 0.15, although C1 and C2 display pronounced photoluminescence in the visible region at room temperature with a lifetime of few tens of nanoseconds. Taking into account the characteristics of their emitting state, we have investigated the capability of C1 and C2 to act as a photosensitiser in redox reactions in different solvents (MeCN, PrCN and DMF). The efficient oxidation and reduction of both complexes under continuous irradiation in the presence of a sacrificial electron acceptor or donor is reported here. The photo-induced transformations and the nature of the resulting compounds were analysed by UV/Vis and IR spectroscopies and cyclic voltammetry. Photo-induced oxidation of C1 and C2 leads to the corresponding monocarbonyl oxidised species, whereas photo-induced reduction under argon leads mainly to the formation of the corresponding Os-bonded molecular wires P1 and P2 after exchange of two electrons associated with the loss of two chloro ligands. The chemical yield of the latter reaction (around 65%) becomes quantitative by adding [Ru(bpy)(3)](2+) as an external redox photosensitiser. This behaviour has been used to photocatalyse the two electron, two proton conversion of CO(2) to CO. Turnover numbers (TON) of 11.5 and 19.5 have been obtained respectively for C1 and C2 after 4.5 h of irradiation under CO(2) in DMF with triethanolamine as the electron donor. TON can be slightly increased by adding [Ru(bpy)(3)](2+) to the solution. 相似文献
4.
Emil Tashev Tania Tosheva Stoycho Shenkov Anne-Sophie Chauvin Victoria Lachkova Rosica Petrova 《Supramolecular chemistry》2013,25(7):447-457
The synthesis and characterization of several new phosphorus-containing partially lower rim substituted derivatives of 5,11,17,23-tetra(t-butyl) calix(4)arene (I) and 5,11,17,23-tetra(t-octyl)calix(4)arene (II), namely 5,11,17,23-tetra(t-butyl)-25,27-dihydroxy-26,28-bis(diphenylphosphinoyl-oxy) calix(4)arene (IV); 5,11,17,23-tetra(t-butyl)-25-hydroxy-26,27,28-tris(tetramethyldiamido-phosphinoyl-oxy) calix(4)arene (Vb); 5,11,17,23-tetra(t-butyl)-25,27-dihydroxy-26,28-bis(dimethyl-phosphinoyl-methoxy) calix(4)arene (VI); 5,11,17,23-tetra (t-octyl)-25,27-dihydroxy-26,28-bis(dimethyl-phosphinoyl-methoxy) calix(4)arene (VII) are reported. The structure of the synthesized calix(4)arene derivatives are identified and confirmed by elemental analysis, IR, 1H, 13C, 31P{1H} NMR spectroscopy and mass spectrometry as and X-ray crystallographic analysis of 5,11,17,23-tetra(t-butyl)-25,27-dihydroxy-26,28-bis(dimethyl-phosphinoyl-methoxy) calix(4)arene VI. According to the NMR spectra, all calix(4)arenes are in cone conformation. 相似文献
5.
6.
Shishkin OV Zubatyuk RI Dyakonenko VV Lepetit C Chauvin R 《Physical chemistry chemical physics : PCCP》2011,13(15):6837-6848
Model complexes of hexaethynylhexamethoxy[6]pericyclyne (HM6P) molecules, with or without dichloromethane (DCM) guests, have been calculated at the M05-2X/6-311G(d,p) DFT level. Analysis of nonbonding interactions shows that the cohesion of the supramolecular tubular assemblies previously observed in the crystal state, relies mainly on C-H···O hydrogen bonds between axial ethynyl and equatorial methoxy substituents of stacked HM6P C(18) macrocycles in a cyclohexane-like chair conformation. The intrinsic binding energy of one HM6P molecule with two neighbors is calculated to be more than 40 kcal mol(-1). The inner channel of the stacks (of ca. 8 ? diameter) are suitable for hosting DCM molecules. Using the Atoms In Molecules (AIM) theory, the interaction between DCM molecules and surrounding triple bonds is analyzed in terms of σ-hole-directed C-Cl···π halogen bonds. A σ-hole-directed Cl···Cl interaction between two chlorine atoms of different DCM molecules is also evidenced. 相似文献
7.
Jean-Claude G. Bünzli Anne-Sophie Chauvin Hwan Kyu Kim Emmanuel Deiters Svetlana V. Eliseeva 《Coordination chemistry reviews》2010,254(21-22):2623-2633
The photophysical parameters for the sensitization of metal-centred luminescence are analyzed in two series of complexes with tridentate and hexadentate ligands having NxOy chelating units. In particular, the radiative lifetime τrad is experimentally estimated for 29 nine-coordinate EuIII complexes and 10 eight- and nine-coordinate YbIII complexes. The known dependence of τrad on refractive index is substantiated by comparing data for solid-state samples and solutions. Moreover, a clear dependence of τrad with the coordination environment is evidenced and in the case of EuIII, a comparison between τrad and the nephelauxetic effect generated by the ligands is attempted. Altogether, this extensive analysis points to the importance of having a handle on τrad when designing ligands for highly luminescent lanthanide-containing molecular edifices. This, in turn, should stimulate initiating theoretical considerations to unravel a reliable relationship between τrad and the electronic structure of the ligands. 相似文献
8.
Zoia V. Voitenko Oleksandr I. Halaev Sergey V. Kolotilov Christine Lepetit Bruno Donnadieu Remi Chauvin 《Tetrahedron》2010,66(41):8214-8222
Base- and acid-catalyzed nucleophilic addition of 11H-isoindolo[2,1-a]quinazoline-5-one to aromatic aldehydes and maleimides was investigated. The aldol adducts and condensation products were obtained stereoselectively. Main diastereomers of the Michael adducts were isolated in 74-89% yield, and converted by N-methylation to new stable α-substituted isoindole derivatives, for which 6-methylisoindolo[2,1-a]]quinazoline-5-one stands as the unsubstituted reference. The stability of the latter was monitored in moist aerated CDCl3 solution, and one of the oxidative hydrolysis product was characterized by X-ray diffraction analysis as the corresponding N-arylphthalimide. The reactivity of the unsubstituted 6-methylisoindolo[2,1-a]]quinazoline-5-one was also investigated with acetylenic Michael acceptors. Fully conjugated isoindole derivatives possessing an original pull-push-pull structure were obtained. The conformations and molecular orbitals of the dibenzoylacetylene adduct were studied at the DFT level of theory. Its static quadratic hyperpolarizabilty β0 was also calculated at the ZINDO level. 相似文献
9.
Remigiusz Zurawinski Christine Lepetit Yves Canac Laure Vendier Marian Mikolajczyk Remi Chauvin 《Tetrahedron: Asymmetry》2010,21(13-14):1777-1787
The synthesis and structure of Rh(I) and Pd(II) complexes of chiral P,C-chelating phosphino-(α-sulfinylalkyl)phosphonium ylide ligands with a trisubstituted asymmetric ylidic center P+–C1R(S1(O)p-Tol)–M (R = alkyl group) have been investigated, and compared to those of the analogous disubstituted ylide complexes (R = H). Reaction of the ethyl onium ylide of o-bis(diphenylphosphino)benzene with (?)-menthyl-(S)-p-tolylsulfinate afforded the corresponding racemic erythro phosphino-(α-sulfinylethyl)phosphonium in 90% de (R = Me). The racemization process is interpreted by a Berry-like pseudorotation mechanism driven by the steric repulsion between the α-methyl substituent and the bulky menthyloxy S-substituent or sulfur lone pair in the intermediate ylide-sulfinyl adduct. The ylide of phosphino-(α-sulfinylethyl)phosphonium reacts with [Rh(cod)2][PF6] and PdCl2(MeCN)2 to afford the corresponding P,C1-chelated threo-Rh(I) and erythro-Pd(II) mononuclear complexes in 70% yield and total diastereoselectivity. These respective complexes act as efficient catalytic precursors for the hydrogenation of (Z)-α-acetamidocinnamic acid and allylic substitution of 3-acetoxy-1,3-diphenyl-1-propene with sodium dimethyl malonate. The bonding features of the erythro-Pd(II) complex exhibiting a sulfinyl O?Pd interaction are studied theoretically at the DFT level using ELF and MESP analyses. The η2-P,C haptomeric form of the ylide ligand is estimated to compete at 19% with the η1-C haptomeric form dominating at 81%. 相似文献
10.