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71.
The present work is dedicated to the XRD, ED and HREM characterization of a new bismuth copper oxyphosphate Bi∼6.2Cu∼6.2O8(PO4)5 (a=11.599(2)Å, , c=37.541(5)Å, R1=0.0755, Rw2=0.174, G.S Pn21a). The relatively long size of its c parameter is due to the arrangement along this direction of two kinds of ribbon-like polycations formed by edge sharing O(Bi, Cu)4 tetrahedra. The existence of such cations is characterized by the b∼5.2 Å value intrinsic to the ribbons structure and commonly found in bismuth oxyphosphate materials. In the title compound, 2-tetrahedra wide [Bi∼2.4Cu∼3.6O4]6.4+ and 3-tetrahedra wide [Bi∼5Cu∼3O6]9+ ribbons are isolated by phosphate groups and alternate along c. The interstitial site created between two different sizes ribbons is occupied by Cu2+ cations disordered over several close crystallographic sites. The mixed Bi3+/Cu2+ nature of certain edge-of-ribbons positions induces a disorder over several configurations of the phosphate groups. The concerned oxygen atoms form the environment of the disordered interstitial Cu2+ cations which occupy tunnels formed by the phosphate anions. The high-resolution electron microscope study enables a precise correlation between the observed images and the refined crystal structure, evidencing the polycations visualization. Furthermore, this material being the second example of partially disordered compound similar chemical system, some topological rules can be deduced. The b-axis doubling was observed by ED and HREM and is assigned to the ordering of interstitial Cu2+ within tunnels cations. A partial intra-tunnel ordering was also observed. 相似文献
72.
Ramadan Ahmed Mekheimer Kamal Usef Sadek Hisham Ahmed Abd El‐Nabi Afaf Abd El‐Hameid Mohamed Ehab Anwer Ebraheem Michael B. Smith 《Journal of heterocyclic chemistry》2005,42(4):567-574
Ethyl 3‐amino‐4‐chlorothieno[3,2‐c]quinoline‐2‐carboxylate ( 4 ) is a versatile synthon, prepared by reacting an equimolar amount of 2,4‐dichloroquinoline‐3‐carbonitrile ( 1 ) with ethyl mercaptoacetate ( 2 ). Ethyl 5‐alkyl‐5H‐1‐thia‐3,5,6‐triazaaceanfhrylene‐2‐carboxylates 9a‐c , novel perianellated tetracyclic heteroaro‐matics, were prepared by refluxing 4 with excess of primary amines 7a‐c to yield the corresponding amino‐thieno[3,2‐c]quinolines 8a‐c . Subsequent reaction with an excess of triethyl orthoformate (TEO) furnished 9a‐c . Reaction of 4 with TEO in Ac2O at reflux, gave the simple acetylated compounds, thieno[3,2‐c]‐quinolines 12 and 13 . Refluxing 4 with benzylamine ( 7d ) gave 10 , and subsequent treatment with TEO gave the tetracyclic compound 11 . Refluxing 13 with an excess of alkylamines 7a‐d gave the fhieno[3,2‐c]quino‐lines 15 . Refluxing the aminothienoquinolines 8b with an excess of triethyl orthoacetate gave thieno[3,2‐c]quinoline 17 , while heating with Ac2O gave 18 and 19 , with small amounts of 16 . Reaction of 8a,b with ethyl chloroformate and phenylisothiocyanate generated the new 1‐thia‐3,5,6‐triazaaceanthrylenes 20a,b and 21a,b , respectively. Diazotization of 8a‐c afforded the novel tetracyclic ethyl 5‐alkyl‐5H‐1‐fhia‐3,4,5,6‐tetraazaaceanthrylene‐2‐carboxylates 22a‐c in good yields. 相似文献
73.
74.
A. M. El-Kot S. Abd El Haleem S. Mohammed 《Monatshefte für Chemie / Chemical Monthly》1992,123(11):965-975
Summary The potentiodynamic polarization of the iron electrode in sulphuric acid solutions was studied. The formation of a passivating film on the electrode upon anodic oxidation in sulphuric acid solution depends on the concentration of the acid. Addition of Cl– ions to sulphuric acid solutions raises the current densities along both the active and passive regions. The difference between the dissolution current in halogen-containing media and solutions devoid of these ions, i. e., the enhancing effect of Cl– ions, i, varies with the aggressive ions concentration according to log i=a
5+b
5 logC
agg. Organic carboxylates enhance the active dissolution of iron through their participation in the dissolution mechanism, while they inhibit pitting corrosion through competitive adsorption with Cl– ions for adsorption sites on the metal surface.
Elektrochemische Polarisation und Passivierung von Eisen in sauren Lösungen
Zusammenfassung Es wurde die potentiodynamische Polarisierung der Eisenelektrode in schwefelsauren Lösungen untersucht. Die Ausbildung eines passivierenden Films auf der Eisenelektrode nach der anodischen Oxidation hängt von der Säurekonzentration ab. Zugabe von Cl–-Ionen zur Schwefelsäurelösung erhöht die Stromdichten sowohl in den aktiven als auch den passiven Bereichen. Der entsprechende Lösungsstrom mit bzw. ohne diese Ionen, also der verstärkende Effekt der Cl–-Ionen variiert mit der Konzentration der aggressiven Ionen: log i=a 5+b 5 logc agg. Organische Carboxylate verstärken die aktive Lösung von Eisen durch ihre Teilnahme am Lösungsmechanismus, andererseits inhibieren sie Narben-Korrosion, da sie mit den Cl–-Ionen bezüglich möglicher Adsorptionsstellen an der Metalloberfläche konkurrieren.相似文献
75.
Wojciech Duczmal Beata Maciejewska Elżbieta Śliwińska Bogdan Marciniec 《Transition Metal Chemistry》1995,20(2):162-165
Summary Trisubstituted silanes, HSiR3–n
X
n
(R = Me, Et, Pr or Bu; X = Cl, OEt or Ph; and n = 0–3) readily undergo oxidative addition to complex [RhCl(cod)PPh3] (where cod = cycloocta-1,5-diene).The quantitative correlation between rate constants, k
1, of the reaction, followed spectrophotometrically at 20 °C in benzene solutions, and the structure of tri-substituted silanes represented by stereoelectronic parameters , and E of the substituents, was established: logk
1 = a + b + c + dE. The reaction rate is accelerated by electron-withdrawing substituents at silicon and retarded by the bulk and pd donation of nonalkyl substituents.Author to whom all correspondence should be directed. 相似文献
76.
1H NMR chemical shifts of solutions of the following cationic surfactants in D2O were determined as a function of their concentrations: cetyltrimethylammonium chloride, CTACl, a 1 : 1 molar mixture of
CTACl and toluene, cetylpyridinium chloride, CPyCl, cetyldimethylphenylam-monium chloride, CDPhACl, cetyldimethylbenzylammonium
chloride, CDBzACl, cetyldimethyl-2-phenylethylammonium chloride, CDPhEtACl, and cetyldimethyl-3-phenylpropylammonium chloride,
CDPhPrACl. Plots of observed chemical shifts versus [surfactant] are sigmoidal, and were fitted to a model based on the mass-action
law. Satisfactory fitting was obtained for the discrete protons of all surfactants. From these fits, we calculated the equilibrium
constant for micelle formation, K, the critical micelle concentration, CMC and the chemical shifts of the monomer, δmon and the micelle δmic. 1H NMR-based CMC values are in excellent agreement with those which we determined by surface tension measurements of surfactant
solutions in H2O, allowing for the difference in structure between D2O and H2O. Values of K increase as a function of increasing the size of the hydrophilic group, but the free energy of transfer per CH2 group of the phenylalkyl moiety from bulk water to the micellar interface is approximately constant, 1.9±0.1 kJ mol-1. Values of (δmic–δmon) for the surfactant groups at the interface, e.g., CH3–(CH2)15–N+(CH3)2 and within the micellar core, e.g., CH3–(CH2)15–N+ were used to probe the (average) conformation of the phenyl group in the interfacial region. The picture that emerges is
that the aromatic ring is perpendicular to the interface in CDPhACl and is more or less parallel to it in CDBzACl, CDPhEtACl,
and CDPhPrACl.
Received: 23 February 1996 Accepted: 29 August 1996 相似文献
77.
Wagner-Czauderna Elżbieta Boroń-Cegiełkowska Agata Orłowska Elżbieta Kalinowski Marek K. 《Transition Metal Chemistry》2004,29(1):61-65
The visible absorption spectra of CoCl2 in binary mixtures of acetone, dmf, dma and dmso with H2O show the existence of configuration equilibria between tetrahedral (T) and octahedral (O) species. Linear correlations between the values of log K (K = [O]/[T]) and the mole fraction of H2O,
w, have been observed in all the systems under study; their slopes decrease linearly with an increase of the donor number, DN, of the organic component of the mixture. The formation of octahedral species is enthalpy favoured but entropy disfavoured. It was found that both H and S values change linearly with
w and the slopes of these relationships depend clearly on the DN values. 相似文献
78.
S. Allaoud H. Bitar M. El Mouhtadi B. Frange 《Journal of organometallic chemistry》1983,248(2):123-130
13C NMR spectra and complete assignment by means of coupled spectra and off resonance experiments, are reported for a new kind of organoboron heterocycle and the related borazine (o-CH3C6H4NBCH3)3; π-charge densities, obtained from LCAO-MO Hückel calculations, are in reasonable agreement with experimental chemical shifts for the former compound. 相似文献
79.
A fundamental study was made on the reduction of calcium phosphate by carbon. The mechanism of reduction was presented on applying different additions. Both silica and alumina increased the extent of reduction but with variable rates. The activation energies were calculated on the basis of first-order reactions. The phases formed during reduction were investigated by X-ray analysis. 相似文献
80.
E. Betranhandy Samir F. Matar Ch. El‐Kfoury R. Weihrich J. Etourneau 《无机化学与普通化学杂志》2004,630(15):2587-2598
The changes in electronic structure and hardness as inferred from the bulk modulus are investigated for model structures of ternary compounds XC3N3 (X = B, Al, P, As, Ga) within the framework of density functional theory (DFT). The optimisations of the proposed two‐ (2D) and three‐dimensional (3D) structures and the calculations of the bulk moduli are performed by a pseudo potential method. The electronic structures are calculated with the augmented sphere wave method (ASW). The obtained hardness for 2D BC3N3 system (B0 ~ 220 GPa) points to a magnitude close to that of graphitic C3N4. For heavier X atoms it decreases rapidly. This is equally observed for the 3D systems examined in the β‐C3N4 structure for which B0(β‐BC3N3) amounts to ~330 GPa. Within the magnitude of the well known hard material cubic BN, the BC3N3 phases can be predicted as candidates for ultra hard materials. The electronic effect induced by the chemical nature of the X substitutional was examined according to its position in the periodic table i.e. XIII or XV. Both, band structures and the electron localisation function (ELF) were used for this analysis. The ELF plots show a decreasing covalency with heavier X‐atoms. Potential applications of the devised systems are proposed such as dopings with atoms (Li, rare gas) and molecules (N2). 相似文献