Influence of alkaline earth metals on the activity and sulfur stability of zeolites in the Nox−C3−C4 hydrocarbon selective reduction of no to nitrogen (SKV) process

The results of the influence of alkaline earth metal and magnesium cations on the activity and sulfur stability of catalysts based on synthetic mordenites and high-silicon zeolites with pentasil structures on the selective reduction of nitrogen oxides with C₃−C₄ hydrocarbons are presented. Doping the H-form of mordenite and pentasils with Ca, Sr, Ba, and Mg cations increased their activity and stability with respect to sulfur dioxide in the selective reduction of NO_x with a propane-butane mixture. L. V. Pisarzhevskii Institute of Physical Chemistry, Academy of Sciences of Ukraine, 31 Prospekt Nauki, Kiev 252039, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 5, 317–321, September–October, 1999.     

On the α-dioximine complexes of transition metals—LX: The stability of the Fe(II), Co(II) and Ni(II) complexes of 1,2-cycloheptane dione dioxime and 1,2-cyclooctane dione dioxime in dioxane-water mixtures

The acid dissociation constants of the 1,2-cycloheptane dione dioxime (Heptoxime) and 1,2-cyclooctane dione dioxime (Octoxime), as well as the stability constants of the Fe(II), Co(II) and Ni(II) complexes of these ligands were determined by potentiometric titrations, in 75% vol. dioxane—25% vol. water mixtures. On the basis of a relation given in the literature and tested in the case of the studied Fe(II) and Co(II) complexes, the stability constants of the slightly soluble Ni(II) complexes were also extrapolated for aqueous solutions.     

Synthesis and structures of 3-sila-β-diketiminato complexes of the coinage metals

The dimeric copper(I) 3-sila-β-diketiminate [Cu{(N(R)C(Ar))₂SiR}]₂ · (thf) (1) was obtained from CuI and [Li{(N(R)C(Ar))₂SiR}(thf)₂] (B) in toluene (R = SiMe₃, Ar = C₆H₃Me₂-2,6). When [CuI(PPh₃)₃] was used as a starting material, the LiI-containing compound [Cu{Si(R)(C(Ar)N(R))₂Li(μ-I)}(PPh₃)] (2) was isolated. The reaction of [MI(PPh₃)_n] (M = Ag, n = 3; M = Au, n = 2) with two equivalents of B in toluene gave the isomorphous silver and gold 3-sila-β-diketiminates [M{Si(R)(C(Ar)N(R))₂Li}₂(μ-I)] [M = Ag (3), Au (4)]. Each of 1-4 was characterised by the multinuclear NMR spectroscopy and single-crystal X-ray diffraction crystallography.     

Quantum-chemical study of yttrium subgroup LnF 6 3− fluoride complexes

The structural, energetic, and electronic characteristics of the LnF ₆ ^3? hexafluoride complexes (Ln = Tb-Yb) have been calculated by the density functional theory method in the local density approximation.     

Ab initio study of the HCO 3 − /H2O exchange in the (NH3)3 ZnII(HCO 3 − ) complex

Summary The displacement of bicarbonate anion in the (NH₃)₃Zn^II(HCO ₃ ^– ) complex with water has been studied throughab initio calculations. It has been found that H₂O binds to the (NH₃)₃Zn^II(HCO ₃ ^– ) species yielding a stable pentacoordinate (NH₃)₃Zn^II(HCO ₃ ^– )(H₂O) complex. The results also indicate that deprotonation of water in the pentacoordinate species facilitates the release of HCO ₃ ^– , although, the presence of HCO ₃ ^– in the coordination sphere of Zn^II makes such deprotonation more difficult. Environmental effects have been considered in the study of HCO ₃ ^– /H₂O exchange.A contribution from the Grup de Química Quàntica de l'Institut d'Estudis Catalans     

On the inhibition of positronium formation by NO3− ions in different solvents

In previous papers [1, 2] the inhibition of the Ps formation by certain solutes was investigated and a new equation based on a hot Ps reaction model was proposed for describing the dependence of the Ps survival probability on the inhibitor concentration. In this equation a constant K appears which depends both on the reaction cross section of the solute and on the moderating power of the solvent for hot Ps atoms. It was also hypothesized that the moderating power of the solvent molecule should be linearly correlated with the number of its vibrational modes. In the present paper it is reported that the experimental results agree with this hypothesis. The results are also discussed in the framework of the model mentioned above.     

On the stereochemical stability of α-sulfonylvinyllithium compounds

α-Lithiated vinylic sulfones have been prepared from readily available 1-alkenyl sulfones in tetrahydrofuran by treatment with methyllithium at −90°C; they appear to be configurationally unstable at −60°C.     

Static sterochemistry of the β-diketonate complexes of group II metals

The static sterochemistry in solution of the β-diketonate complexes of Be, Mg, Ca, Ba and Zn was investigated using ¹H-NMR techniques. It was ascertained that the bis-acetylacetonate complexes of Mg, Ca and Ba are polymeric in solution, in contrast to the dipivaloylmethanate complexes of Mg and Zn which are monomeric in solution. The benzoylacetonate chelates of all the metals studied were found also to be monomeric in solution. Chemical shift values and other arguments led us to favor a pseudo-tetrahedral D_2d idealized structure for all the complexes investigated.     

IR emission spectra of the AlCl4− ion in AlCl3MCl (M  Li,Na, K) melts

IR emission spectra of MAlCl₄ (M  Li, Na, K) melts are reported.     

On the π coordination of organometallic fullerene complexes

Novel organometallic complexes of fullerene C?? and aryl ligands were simulated. The nature and characteristics of this family of complexes involving π coordination between the fullerene and a metal centre have been studied from a theoretical point of view. We are particularly interested in complexes where η? coordination is present, this being the strangest manifestation of known coordinations, and thus we have studied several known and simulated compounds of this kind in order to understand the lack of examples. The presence of other η? or η? ligands on the opposite side seems to be an important element aiding the stabilization of these complexes, also inducing the conductive and semiconductive behaviour of the studied species.     

Intraconfigurational absorption spectroscopy of IrCl2−6 and IrBr2−6 in A2MX6-type host crystals

Near-IR absorption spectra for Ir⁴⁺ in A₂MX₆ (A  K, Rb, NH₄, M  Sn, Pt, Re, X  Cl, Br)-type hosts are discussed and compared to earlier work. Our data indicate that the effect of reduced host symmetry is quite small in this d⁵ system and that the IrCl²⁻₆ spectra can be interpreted in a manner paralleling previous studies on Ir⁴⁺ in cubic hosts. In some hosts, e.g., K₂PtCl₆, the IrBr²⁻₆ appears to have a vibronic pattern outside the experience with previous MX²⁻₆ results. Origin shifts and the nature of a vibronic progression were seen to correlate with host lattice counterion. By comparison to luminescence results of Flint and Paulusz, the latter data are proposed to be indicative of a strongly Jahn-Teller active e_g mode.     

Kinetic stability of complexes of some d-metals with 3,3′-bis(dipyrrolylmethene) in the binary proton-donor solvent acetic acid-benzene

The kinetics of dissociation of Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and Hg(II) binuclear homoleptic double-stranded helicates with bis(2,4,7,8,9-pentametyldipyrrolylmethen-3-yl)methane (H₂L) of the [M₂L₂] composition in the binary proton-donor solvent acetic acid-benzene was studied. Protolytic dissociation of the helicates [M₂L₂] proceeds in accordance with the third order kinetic equation. Effect of the complexing metal nature is manifested in increased kinetic inertness in the following series of the helicates: [Cd₂L₂] < [Hg₂L₂] < [Cu₂L₂] < [Ni₂L₂] < [Zn₂L₂] < [Co₂L₂]. By the lability in similar environmental conditions the helicates [M₂L₂] are comparable to the metal complexes of distorted porphyrins and are much more inert than dipyrrolylmethenate mononuclear complexes.     

Kinetics of the Oxidation of Phenylhydrazine by [Fe(CN)6]3− in Water‐in‐Oil Microemulsions

The oxidation reaction of phenyl hydrazine (Phh) by hexacyanoferrate ([Fe(CN)₆]^3?) has been studied in water‐in‐oil (w/o) microemulsion media. The kinetic profile of the reaction was investigated as a function of [Phh], droplet size, and droplet concentration. Comparison of the kinetic profiles of the reaction in microemulsion, water‐urea, and water‐AOT‐urea media indicates that the kinetic profile of the reaction in microemulsion shows a behavior similar to that of the reaction in water‐AOT‐urea medium at 4 M urea. An initial increase and then a decrease in k_obs is observed with increasing molar ratio, W_o(=[H₂O]/[AOT]) at constant [AOT] (=0.4 M), whereas k_obs decreases upon increasing the AOT concentration at constant molar ratio.     

Simple fast preparation of neutral palladium(II) complexes with SnCl− 3 and Cl− ligands

A new method for preparing neutral trichlorostannate complexes of Pd^II, based on the interaction between solid [PdCl₂(MeCN)₂] and SnCl₂ suspension and a solution of an appropriate ligand in CH₂Cl₂, has been developed. The analogous method can be used to prepare complexes without tin, as well as compounds containing mixed anionic ligands. A number of complexes (including several new compounds) with amines, phosphines and diene ligands have been obtained by these methods. The procedures are simple and fast – the total preparation time (without recrystallisation) is ca. 30 min.     

Nucleotide hydrolysis in the presence of μ-hydroxo-bridged-cobalt(III) complexes

Abstract

Two cobalt(III) complexes with tridentate ligands, the acyclic diethylenetriamine and macrocyclic 1,4,7-triazacyclononane, were examined as potential catalysts for the hydrolysis of adenosine 5′-triphosphate (ATP). Studies were performed primarily at pH 4.5, where the two complexes were in the binuclear di-μ-hydroxo forms. For both complexes, a rapid initial hydrolysis with first order dependence on the concentration of ATP was observed, k_obs of approximately 0.20 min^?1, followed by very slow hydrolysis. Deuterium isotope studies done in D₂O showed a normal isotope effect with k_H/k_D = 1.8. Spectral investigations and ⁵⁹Co NMR studies indicated that the biphasic nature of the hydrolysis reaction may be due to the formation of a complex in which inorganic phosphate is coordinated to the cobalt, effectively poisoning the catalyst.     

The thermodynamic stability of the LaBr 4 − ion

The thermodynamic stability of the LaBr ₄ ^? anion was for the first time studied by high-temperature mass spectrometry and nonempirical quantum-chemical methods. The experimental and theoretical enthalpies of the reaction $ LaBr_4^ - = Br^ - + LaBr_3 The thermodynamic stability of the LaBr₄⁻ anion was for the first time studied by high-temperature mass spectrometry and nonempirical quantum-chemical methods. The experimental and theoretical enthalpies of the reaction were Δ_r H°(298.15 K) = 302 ± 14 and 303 kJ/mol, respectively. The value Δ_f H° (LaBr₄⁻, g, 298.15 K) = −1105 ± 14 kJ/mol was recommended as the enthalpy of formation of the LaBr₄⁻ anion. Original Russian Text ? M.F. Butman, L.S. Kudin, V.B. Motalov, D.A. Ivanov, V.V. Sliznev, K.W. Kr?mer, 2008, published in Zhurnal Fizicheskoi Khimii, 2008, Vol. 82, No. 5, pp. 885–890.     

On the stereochemistry of chiral (η5-C9H7)Rh(diphosphine) complexes

The dynamic behaviour of some indenyl complexes of the type (η⁵-C₉H₇)Rh(Ph₂PCHRCHR′PPh₂) (R = or ≠ R′) has been investigated, and the relevant energy barrier involved evaluated (10–11 kcal/mol). For the complexes in which the diphosphine has a C₁ symmetry (R ≠ R′), the energy differences between the two diastereometric conformations seem to depend on both steric and electronic factors.     

Ab initio study of the structure and stability of AcF n (3 ? n)+ of complexes (n = 1?7)

The structural and energetic characteristics of AcF _n ^{(3 ? n)+} complexes (n = 1?7) have been calculated by the ab initio RHF and MP2 methods.     

Adsorption of S2− and HS− ions on the (111) face of coinage metals: A quantum-chemical study

The interactions of S^2? and HS^? ions with gold, silver, and copper were studied by density functional theory using the cluster model of the metal surface. The geometrical and energy characteristics of the interactions of these ions with the surface metal atoms were evaluated. The S^2? ions form stronger chemical bonds with the surface metal atoms than HS^? ions. A significant charge transfer from anion to metal occurs during the adsorption. The adsorbability increased in the series Ag < Cu < Au for both anions. The HS^? ion showed greater ability to be transferred to the surface during the electrochemical adsorption due to the strong hydration of the S^2? ion. In alkaline media, however, the dissociation of the adsorbed HS^? leads to its conversion to S^2?.     

Tetramethylammonium hexanitratoneodymiate(III). Structural variations of the [Nd(NO3)6]3− anion in a single crystal

The structure of tetramethylammonium hexanitratoneodymiate(III) has been determined at 123?K in the suprisingly low symmetry space group P 1 considering the simplicity of the compound. The structure has Z′?=?4 with seventeen distinct chemical fragments in the asymmetric unit (12 tetramethylammonium cations, three complete [Nd(NO₃)₆]^3? anions and two half [Nd(NO₃)₆]^3? species situated on special positions). This one structure contains five different coordination geometries of the [Nd(NO₃)₆]^3? species.