Strontium Sorption on Hematite at Elevated Temperatures

Acid–base reactions and surface complexation of Sr(II) at the hematite/water interface have been studied by means of potentiometric titrations at three different temperatures: 25, 50, and 75°C. Equilibrium measurements were performed in 0.1 M NaCl. In the evaluation of equilibrium models for the acid–base reactions and complexation reactions in the three-component system H⁺ ---(FeOH)---Sr²⁺, the constant capacitance model was applied. During the titrations with Sr, aliquots of the suspension were sampled at in several points. The aqueous concentrations of Sr were analyzed by atomic absorption spectrometry. Treatment of data included tests for formation of both inner-sphere and outer-sphere complexes of different stoichiometric composition. The proposed equilibrium model consists of the following surface complexes of inner sphere type: FeOHSr²⁺ and FeOSrOH. Besides the stability constants for the surface complexes, the thermodynamic parameters ΔH and ΔS were evaluated. The combined effect of a decrease in pH_pzc with increasing temperature and positive enthalpies of surface complex formation favors adsorption of Sr at elevated temperatures.     

Syntheses of 1-(3-oxoalkyl)indole-2-3-diones

Hydration of the triple bond in 1-(alkyn-2-yl)indole-2, 3-diones under Kucherov reaction conditions takes place under the orienting influence of the nitrogen atom with formation of an oxo group exclusively at the -carbon atoms.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 483–488, April, 1996.     

X-ray electronic spectra of certain tetraaza macrocyclic complexes of cobalt (III)

The electronic structure-Of several tetraaza macrocyclic complexes of cobalt (III), containing different axial acido ligands was studied using X-ray electron spectroscopy. The bond energies of electrons of nitrogen, cobalt, chlorine, bromide, and sulfur atoms were measured. It was shown that the bond energy of isoelectrons of the macrocyclic ligand nitrogen atoms is not a constant value, but depends on the nature of the additionally coordinated axial ligand, which reflects the cis-effect of the ligands in the macrocyclic complexes.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 4, pp. 497–500, July–August, 1985.     

Effect of the noncoordinated nitrogen atoms in the macroring on the spin equilibria of nickel(II) complexes with penta- and hexaazamacrocygles: new type of ditopic receptors for hydrosulfate anions

For the first time it was observed that nickel(II) complexes with 14-membered macrocyclic ligands that contain additional noncoordinated nitrogen atoms in the macroring exhibit high selectivity with respect to tying up hydrosulfate anions in acidic aqueous solutions. This effect is explained by a specific two-center interaction of the complex with the anion due to the formation of a donor-acceptor bond with the nickel ion and a hydrogen bond with the unshared pair of electrons of the noncoordinated nitrogen atom.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, Nos. 5–6, pp. 436–441, September–December, 1992.     

A comparative effect of ring annelation on cation-benzene and anion-benzene

DFT/B3LYP calculations were carried out on several π-complexes formed by cations and anions with annelated benzene, respectively. The binding energies obtained with standard method were corrected by basis set superposition error (BSSE) and zero-point energy (ZPE) during the geometry optimization for all complexes at the same levels of theory, respectively. Some different aspects of the π–cation have been compared to those of π–anion, involving in binding energy changes in effect of ring annelation, the aromaticity of the ring upon complexation, Mulliken and NBO charge-transfer. The effect of BSSE correction during the optimization is very important in some π–anion complexes whether or not using diffuse functions in basis set, and results with at least one set of diffuse functions 6-31+G(d) basis set is a little better than results obtained by 6-31G(d, p) basis set for some π–anion especially for F⁻ complexes.     

Mechanism of Silver(I)‐Catalyzed Enantioselective Synthesis of Axially Chiral Allenes Based on Propargylamines

The silver(I)‐catalyzed synthesis picture of axially chiral allenes based on propargylamines has been outlined using density functional theory (DFT) method for the first time. Our calculations find that, the coordination of silver(I) into triple bond of propargylamines at anti‐position of nitrogen shows a stronger activation on the triple bond than that at cis‐position, which is favorable for the subsequent hydrogen transfer. The NBO charge analysis for the hydrogen transfer affirms the experimental speculation that this step is a hydride transfer process. The energy barrier of the anti‐periplanar elimination of vinyl‐silver is 26.9 kJ·mol^?1 lower than that of the syn‐periplanar elimination, supporting that (?)‐allene is the main product of this reaction. In a word, the most possible route for this reaction is that the silver(I) coordinates into the triple bond of propargylamines at anti‐position of nitrogen, then the formed silver(I) complex undergoes a hydride transfer to give a vinyl‐silver, finally the vinyl‐silver goes through an anti‐periplanar elimination to give (?)‐allene. The hydride transfer with the energy barrier of 44.8 kJ·mol^?1 is the rate‐limiting step in whole catalytic process. This work provides insight into why this reaction has a very high enantioselectivity.     

Theoretical study on the structures and properties of the isomers of Nn(CH)8−nH8 (n = 0–7)

With replacement of N atoms by CH groups in the most stable chain isomer of N8H8, 34 possible isomers of N_n(CH)_8−nH₈ (n = 0–7) have been designed and optimized at the B3LYP/6-311++G** level of theory. The natural bond orbital (NBO) and atoms in molecules (AIM) analysis are carried out to study the bonding nature and relative stabilities of these conformers. G3MP2 method is applied to calculate energies and heats of formation. The results indicate that the hyperconjugation effect from lone pairs of nitrogen atoms to germinal C–N bonds is the major factor which caused the change of the C–N bond length. With the more replacement of nitrogen atoms by CH groups, the heats of formation of the isomers of N_n(CH)_8−nH₈ (n = 0–7) decrease gradually, but the energies increase linearly.     

A screened hybrid density functional study on energetic complexes: Alkaline-earth metal carbohydrazide perchlorates

The molecular geometries, electronic structures and stabilities of a series of alkaline-earth metal carbohydrazide perchlorates were investigated using the Heyd–Scuseria–Ernzerhof (HSE) screened hybrid density functional. The results show that Be and Mg complexes have six-coordinated octahedron features, as previously reported for the transition metal complexes. However, Ca, Sr and Ba complexes have additional coordinated oxygen atoms from the perchlorate ion. Detailed NBO analyses indicate that the metal–ligand interactions are essentially ionic and play an important role in the stabilities of these energetic complexes. The donor–acceptor interactions result in a reduction of occupancies of σ_C=O and σ_N–H bond orbitals, and also their subsequent impact on bond length and bond order.     

Conformationally rigid hexaazamacrocyclic complexes of nickel(II) as selective hydrosulfate receptors in comparison with dihydrophosphate

It was shown on the example of two-point interaction of hydrosulfate and dihydrophosphate with hexaazamacrocyclic complexes of nickel(II) that the presence of nitrogen atoms in the ligand molecule of conformationally rigid chelate rings with an equatorial unshared pair of electrons leads to a decrease in the anionbonding efficiency; however, it enhances the differentiating effect between them in comparison with the receptor in which the nitrogen atom is included in a conformationally flexible chelate ring.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 30, No. 5, pp. 298–302, September–October, 1994.     

1,1′-Bis(phosphoranylidenamino)ferrocene palladium(II) complexes: An unusual case of dative Fe → Pd bonding

Subtle differences in the electron-richness of nitrogen atoms in 1,1′-bis(phosphoranylidenamino)ferrocenes can change the coordination geometry of their palladium(II) complexes from cis to trans. Trans complexation results in concomitant formation of a relatively short dative Fe-Pd bond of 2.67 Å.     

Nonempirical quantum chemical calculation for nitramide,its chloro- and methyl-substituted derivatives. I. Structure of equilibrium forms

We have carried out quantum chemical calculations for a series of N-nitramines (H₂NNO₂, MeNHNO₂, CINHNO₂, MeNClNO₂, Me₂NNO₂) using the GAUSSIAN-90 program by the restricted Hartree—Fock method, taking into account electron correlation according to Møller—Plesset second-order perturbation theory in a standard 6–31G^* basis. In this paper, we present the geometric parameters of the equilibrium forms of the molecules obtained as a result of full optimization. The calculation allowed us to establish that with an increase in electronegativity of the substituents on the amine nitrogen atom, we observe coordinated lengthening of the NN bond, shortening of the N=O bond, and increase in the pyramidal character of the configuration of the bonds of the amine nitrogen atoms. We observed a close to linear relationship between the length of the NN bond and the magnitude of the angle of deviation of this bond from the plane of the ONO atoms. The greatest difference in NN bond lengths (0.06 Å) occurs between the Me₂NNO₂ and ClNHNO₂ molecules.Moscow State University. Translated from Zhurnal Strukturnoi Khimii, Vol. 34, No. 1, pp. 4–11, January–February, 1993.     

Effect of composition of coordination sphere on value of constant of additional hyperfine structure of EPR spectra

Conclusions Replacing the oxygen atoms by sulfur atoms in the coordination sphere of nitrogen-containing copper complexes leads to a substantial increase in the constant of the additional hyperfine structure from the nitrogen atoms, and consequently also to an increase in the degree of covalency of the Cu-N bonds.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 704–706, March, 1974.The authors thank V. I. Nefedov for taking the x-ray electronic spectra of compounds (I) and (II).     

The electrostatic potential at atomic sites as a reactivity index in the hydrogen bond formation

The paper reviews results from computational studies by molecular orbital and density functional theories on several series of hydrogen bonded complexes. These studies aim at quantifying the reactivity of molecules for the complexation process. Excellent linear relationships are found between the electrostatic potential values at the sites of the electron donor and electron accepting atoms and the energy of hydrogen bond formation (ΔE). The series studied are: (a) complexes of R–CHO and R–CN molecules with hydrogen fluoride; (b) complexes of mono-substituted acetylene derivatives with ammonia; (c) (HCN)_n hydrogen bonded cluster for n=2–7. All 22 studied complexes of carbonyl and nitrile compounds with hydrogen fluoride fall in the same dependence between the energy of hydrogen bond formation and the electrostatic potential at the atomic site of the carbonyl oxygen and nitrile nitrogen atoms, with linear regression correlation coefficient r=0.979. In the case of complexes of mono-substituted acetylene and diacetylene derivatives with NH₃, the correlation coefficient for the dependence between the electrostatic potential at the acidic hydrogen atom and ΔE equals 0.996. For the series of hydrogen bonded (HCN)_n clusters, the correlation coefficient for the relationship between the electrostatic potential at the end nitrogen atom and ΔE is r=0.9996. Similarly, the analogous relationship with the electrostatic potential at the end hydrogen atom has a regression coefficient equal to 0.9994. The dependencies found are theoretically substantiated by applying the Morokuma energy decomposition scheme. The results show that the molecular electrostatic potential at atomic sites can be successfully used to predict the ability of molecules to form hydrogen bonds.     

Complexation of iodine with macrocyclic polyethers and sulfides

The complexation of iodine with 12-, 15-, and 18-membered crown ethers containing two sulfur atoms in the macrocyclic ring was studied by the spectrophotometric method. It was shown that, in CCl₄, the stability constants of complexes with a 11 composition have a value of the order of magnitude of 10². The enthalpies of complexation are (22–34) kJ/mole, which is practically not different from the parameters of complexes of iodine with simple sulfides.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 6, pp. 747–750, November–December, 1988.     

Synthesis and spectral studies of gold(III) complexes with guanidine derivatives

New trivalent gold (d⁸ electronic configuration) halide complexes with guanidino–pyrimidines have been synthesized and delineated. The complexes have been identified and characterized by elemental analysis, u.v.–vis. electronic absorption spectra, i.r. oscillation spectra and by ¹H-n.m.r. and ¹³C-n.m.r. spectra. All substituted guanidine ligands in these chelates form part of a six-membered pseudo-heterocyclic ring where the nitrogen atoms of the guanidine group and the nitrogen atom of pyrimidine, piperidine or the morpholine heterocyclic ring bond to the metal.     

The Mechanism of Selective NO<Subscript>x</Subscript> Reduction by Hydrocarbons in Excess Oxygen on Oxide Catalysts: IV. Spectrokinetic Characteristics of Intermediate Complexes on the Commercial STK Catalyst

Surface nitrite-nitrate and acetate compounds were detected under conditions of the selective reduction of nitrogen oxides by propane on the STK iron-chromium oxide catalyst using spectrokinetic measurements. The rate of conversion of these complexes under reaction conditions was measured. The resulting values were compared to the rate of the process. The results of this comparison indicated that, at low temperatures (to ∼250°C), the rate of reduction of nitrogen oxides was determined by the interaction of surface nitrite-nitrate complexes with the activated hydrocarbon. The amount of acetate complexes on the surface increased with temperature. A reduction of the surface was also observed as the temperature was increased. The reaction of NO decomposition began on the reduced surface. Nitrogen atoms recombined, and oxygen atoms reacted with the hydrocarbon to form CO₂ in a gas phase. A distinctive feature of the STK catalyst is its ability to form the products of propane mild oxidation and/or oxidative dehydrogenation. From a synergistic standpoint, the STK catalyst is an effective supplier of the activated hydrocarbon, whereas the NTK-10-1 catalyst well activates NO_x. This fact explains the nonadditivity effect observed in the catalytic properties of mechanical mixtures of these catalysts.__________Translated from Kinetika i Kataliz, Vol. 46, No. 4, 2005, pp. 559–568.Original Russian Text Copyright © 2005 by Tret’yakov, Burdeinaya, Zakorchevnaya, Zakirova, Bakhtiyarov, Matyshak, Korchak.     

Theoretical study of the interaction of a proton with the O, F and Cl atoms of enflurane (CHFCl–CF2–O–CHF2)

Ab initio MP2 and density functional B3LYP calculations were performed to investigate the interaction of a proton with the O, F and Cl atoms of enflurane (CHFCl–CF₂–O–CHF₂) in the gas phase. The study included the optimized structures, proton affinities, interactions energies and thermodynamic properties of protonated enflurane. The proton affinities (PAs) of the O and Cl atoms are 154.5 and 139.8 kcal mol⁻¹, respectively, whereas PAs of five of the fluorine atoms are between 143.6 and 165.5 kcal mol⁻¹ (MP2 results). In contrast to protonation at the O and Cl atoms, protonation at each of the F atoms of enflurane reveals a striking result, it leads to a cleavage of the C–F bond and formation of an ion–dipole complex between the enfluranyl cation and neutral hydrogen fluoride. The [(enfluranyl)⁺FH] complexes are weakly bound, the SAPT-calculated interaction energy varies between −12.5 and −11.7 kcal mol⁻¹. The long range attraction in these complexes is dominated by the electrostatic term (70%), whereas the induction and dispersion components contribute by about 15% each. Protonation at the chlorine atom of enflurane does not lead to a cleavage of the C–Cl bond. For the O-protonated enflurane the results from the natural bond orbital analysis (NBO) are discussed in details.     

<Emphasis Type="Italic">In situ</Emphasis> IR Spectroscopic and XPS Study of Surface Complexes and Their Transformations during Ammonia Oxidation to Nitrous Oxide over an Mn-Bi-O/α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Catalyst

Surface complexes resulting from the interaction between ammonia and a manganese-bismuth oxide catalyst were studied by IR spectroscopy and XPS. At the first stage, ammonia reacts with the catalyst to form the surface complexes [NH] and [NH₂] via abstraction of hydrogen atoms even at room temperature. Bringing the catalyst into contact with flowing air at room temperature or with helium under heating results in further hydrogen abstraction and simultaneous formation of [N] from [NH₂] and [NH]. The nitrogen atoms are localized on both reduced (Mn²⁺) and oxidized (Mn^δ+, 2 < δ < 3) sites. Atomic nitrogen is highly mobile and reacts readily with the weakly bound oxygen of the oxidized (Mn^δ+-N) active site. The nitrogen atoms localized on oxidized sites play the key role in N₂O formation. Nitrous oxide is readily formed through the interaction between two Mn^δ+-N species. N₂ molecules result from the recombination of nitrogen atoms localized on reduced (Mn²⁺-N) sites.__________Translated from Kinetika i Kataliz, Vol. 46, No. 4, 2005, pp. 590–600.Original Russian Text Copyright © 2005 by Slavinskaya, Chesalov, Boronin, Polukhina, Noskov.     

Chiral complexes of Pt with amino acids: synthesis,structure, properties

Short review of syntheses of Pt(II) and Pt(IV) chiral complexes with amino acid ligands and their chemical and spectral studies (IR, electronic absorption, circular dichroism, and NMR spectra) is presented. X-ray diffraction data are reported for key chiral amino acid complexes of Pt and absolute configurations of asymmetric atoms of coordinated ligands are determined. The effect of the absolute configurations of asymmetric carbon, nitrogen, and sulfur atoms of the ligands on optical activity of complexes and on the rates of chemical and biochemical reactions is established.Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 2, 2005, pp. 83–92.Original Russian Text Copyright © 2005 by Slyudkin, Tulupov.Dedicated to memory of L.M. Volshtein (1904–1983), Professor of Novosibirsk State University D.Sc. (Chem) and O.N. Adrianova (1918–2002), senior associate of Kurnakov Institute of General and Inorganic Chemistry, RAS, who actively participated in most of the studies covered in this review.     

Motion of protons in the central opening of porphyrins

The distribution of the electrostatic potential of the molecule of porphine (P) and the anions formed by the successive elimination of one and two central protons from it has been studied by the SCF-MO-LCAO method in the all-valence-electron CNDO/2 approximation. The electrostatic potential of the potential of the (P-2HO^2– dianion is characterized by the presence of four minima located at a distance of about 1 Å from the nitrogen atoms. The potential in them is equal to –991 kJ/mole. The value of the potential at the center of the opening is –978 kJ/mole. The distribution of the electrostatic potential of the (P-H)^– anion with a fixed position of the proton near one of the nitrogen atoms is characterized by the presence of a deep valley situated at the oppositely lying nitrogen atom perpendicularly to the N-H bond. The potential of the molecule of P in the plane of the ring does not have negative values, attesting to the energetic unfavorability of the planar conformations of the (P+H)⁺ cation.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 2, pp. 216–220, March–April, 1986.