Iron(II) and iron(III) complexes of 2,4-dithiobiuret

Summary Ferrous and ferric complexes of 2,4-dithiobiuret (Dtb) of the type Fe(Dtb)_m Xn where m, n = 1-3, and X = CI^–, Br^–, I^– and SO ₄ ^2– , and a neutral Fe(Dtb-H)2 complex have been synthesized and characterised by elemental analyses, magnetic susceptibility, i.r., electronic and Mössbauer spectroscopic studies. From its i.r. spectrum Dtb was found to act as a S,S-coordinating bidentate chelate. The magnetic moment, electronic and Massbauer spectra are consistent with a low spin distorted octahedral structure for the ferric complexes and a high spin form for ferrous complexes.     

Radiation Chemistry of Organic Molecules in Solid Rare Gas Matrices: 2. Selective Deprotonation of the Primary Radical Cations upon Irradiation of Oxygen-Containing Molecules in Xenon Matrices

The composition of radical products trapped after irradiation of various ethers (dimethyl ether, tetrahydrofuran, methylal, 1,3-dioxolane) or acetaldehyde in xenon matrices at 15–17 K in the presence of electron scavengers was studied by an ESR technique. It was shown that the primary radical cations give corresponding deprotonation products (carbon-centered radicals), rather than stabilize in xenon, under the given experimental conditions. The deprotonation process is characterized by extremely high selectivity; i.e., the only type of radicals resulting from deprotonation at maximum spin density position was observed in each of the cases. The possible mechanism of the reactions and the nature of their selectivity are discussed.     

Synthesis and magnetic properties of dithiooxamide-bridged nickel(II) complexes

Two novel nickel(II) dinuclear complexes [Ni2(cyclam)2- (DTA)](ClO4)2 (1) and [Ni2(TAA)2(DTA)] (ClO4)2 (2) (TAA=N(CH2CH2NH2)3 , cyclam = 1,4,8,11-tetraazacyclotetradecane, DTA=dithiooxamide) have been prepared and studied by elemental analyses, i.r. and electronic spectra and magnetic measurements. The magnetic susceptibility temperature dependence was measured over the 77–300K range and the observed data were successfully simulated by an equation based on the spin Hamiltonian operator (H=–2JS1S2) giving the exchange integral J=–23.09cm–1 for (1) and J= –26.0cm–1 for (2).     

Conversion of methanol on a high-silica zeolite with divalent cations

The influence of divalent cations introduced into a high-silica zeolite by an ion exchange on its acidity and catalytic properties has been studied. The nature of the divalent cations has an influence on the distribution of the acid sites according to their strength, as well as on the activity and selectivity of action of the zeolite in the conversion of methanol. The primary conversion products of methanol, viz., dimethyl ether and ethylene, form on the acid sites of moderate strength. The hydrogen-redistribution reactions take place predominantly on the strong acid sites.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 1, pp. 114–118, January–February, 1986.     

Effect of a magnetic field on thermostimulated chemiluminescence

Conclusions Effects, associated with relaxation of the spins and the rates of the electronic transitions as a function of the spin states, which determine the sensitivity of processes to an external magnetic field, can be observed in thermally stimulated chemical reactions.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2355–2356, October, 1974.     

Chemical composition and ion exchange properties of zeolites

Series of exchange selectivity for alkali cations in zeolites change in a regular manner in dependence on the ratio (z) between the number of particles capable of solvating cations in the frameworks of zeolites (molecules of zeolite water, one-fourth of the framework oxygen ions) and the number of zeolite cations. For z=5–6 zeolites have maximum selectivity for large cations, for z<3–4 they selectively absorb sodium, while if z<2 they selectively absorb lithium. An analysis is given of the reasons of this dependence of the ion exchange selectivity of zeolites on the chemical composition of their frameworks. It is shown that the free energy of solvation of cations in zeolites is less than the free energy of their hydration. The effect of transformation of the selectivity series of zeolites can be connected with the contribution, on the part of the effect of redistribution of water between the solid and liquid phases of the ion exchange system, to the free energy of ion exchange reactions, which differs in dependence on the composition and structure of the crystals.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 3, pp. 378–382, May–June, 1990.     

Generation of a heterobimetallic FeMoS system containing intermediate spin [FeIIN4S2] functionality: Synthesis,characterisation and redox chemistry of [(N–N)2FeS2MoS2] (N–N=bipy or phen)

Tetrathiomolybdate reacts with iron (II) in the presence of bidentate ligands to form neutral binuclear complexes [Fe(N–N)₂MoS₄] [N–N=2-2bipyridine(bipy) and 1,10-phenanthroline(phen)] showing intermediate spin character for Fe^II. The spin state of the complexes has been examined by variable temperature magnetic moment (VTM) measurements and by variable temperature Mössbauer spectroscopy. The Mössbauer spectra indicate the presence of two iron sites: one of intermediate spin and the other of low spin at room temperature. The low spin site predominates over the intermediate spin as the temperature is lowered. The structural features of the complexes are supported by i.r., Raman, electronic and FAB mass spectra and by X-ray powder diffraction data. Substitution of one bipy/phen ligand in [Fe(N–N)₃]²⁺ by MS₄ ^2– ligands does not impart any major effect towards the size of the redox potentials of the tris-bipy/phen complexes, although the reversible nature of their cyclic voltammetric response is affected.     

The first oxalato-bridged dinuclear CoII–VIVO complexes: synthesis and magnetism

Two novel CoII–VIVO oxalato complexes have been synthesized and characterized, namely [CoL2VO(OX)2·3H2O [L = 1,10-phenanthroline (phen) or 2,2-bipyridyl (bipy), OX = oxalate dianion]. Based on i.r. and electronic spectra and elemental analyses, extended oxalato-bridged structures consisting of VO2+ and CoII species, in which each VIV has a distorted square pyramidal environment and each CoII has a distorted octahedral environment are proposed for the two complexes. The temperature dependence of the magnetic susceptibility for [CoL2VO(OX)2]·3H2O (L = phen, bipy) was measured over the 77–300 K range and the observed data were successfully simulated by an equation based on the spin Hamiltonian operator H^=–2JS^1S^2 giving the exchange integral J=–62.5 cm–1 and J=–40.3 cm–1 for the phen and bipy complexes, respectively. These indicate antiferromagnetic spin exchange interaction between the CoII and VO2+ centres.     

Metal chelates of heterocyclic nitrogen containing ketones,Part IX. Magnetic and spectral studies of the dimeric copper(II) complex of 2-picolyl methyl ketone semicarbazone and its ligation by solvent molecules

Summary The preparation and characterization of [(PMKSC-H)Cu]₂Cl₂ by i.r. electronic and e.s.r. spectra as well as variable temperature magnetic susceptibility are described and a square planar geometry is assumed for the isolated complex. The magnetic susceptibility data indicates overall antiferromagnetic spin coupling. The variable temperature magnetic susceptibility in conjunction with the best fitting procedure yielded: 2J=–46cm^–1, g=2.15 and 6=–5 K. E.s.r. data confirm the existence of spin-spin coupling with D=0.0398 cm^–1. The g-values obtained from the e.s.r. studies were g₁₁=2.24, g=2.08 and g_av.=2.13. The results were used to estimate the Cu-Cu separation in the dimer. The problem of ligation of the dimeric copper(II) complex by various organic solvents was investigated. E.s.r., i.r. and electronic spectra together with the magnetic susceptibiliy studies indicate that [(PMKSC-H)Cu]₂Cl₂ dissociated in polar solvents to give the adducts [(PMKSC-H)CuL_s]Cl which were isolated and characterized.     

Radical hydroxylation of aromatic hydrocarbons examined by MINDO/3 methods

MINDO/3 calculations have been made on the potential-energy surfaces for the attachment of OH^. radicals to benzene (1) and naphthalene (2) in the vapor state. The activation energies of these reactions are calculated as 88 and 58 kJ/mole. while the enthalpies at 298K are calculated as –211 and –199 kJ/mol. The transition states in (1) and (2) lie closer to the reagents than the products on the reaction coordinate, while (1) has an earlier transition state than does (2). The transition states in these reactions have high dipole moments: 3.1 and 3.6 D, respectively, which are due to charge transfer from the hydrocarbons to the OH^.. Quantum-chemical calculations and kinetic data on the reactions of aromatic hydrocarbons with OH^. in aqueous solution indicate that the mechanism is probably not one involving electron transfer and a rate-limiting stage in the attachment. These processes are of high performance because the radicals are of high stability, while polar effects determine the selectivity.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 1, pp. 20–26, January–February, 1986.     

Synthesis and magnetism of tetrachlorophthalato-bridged cobalt(II) binuclear complexes

Three new cobalt(II) binuclear complexes have been prepared and characterized, namely [Co2(TCPHTA)(L)4](ClO4)2 [L=1,10-phenanthroline (phen), 5-nitro-1,10-phenanthroline(NO2-phen) and 2, 2-bipyridyl (bipy), respectively], where TCPHTA is the tetrachlorophthalate dianion. Based on i.r. spectra, elemental analyses and conductivity measurements, tetrachlorophthalato-bridged structures consisting of two cobalt(II) ions in which each cobalt(II) ion has a distorted octahedral environment are proposed for these complexes. The temperature dependence of the magnetic susceptibility for [Co2(TCPHTA)(L)4](ClO4)2·nH2O (L=phen, NO2-phen and bipy) has been measured over the 77–300 K range and the observed data successfully simulated by an equation based on the spin Hamiltonian operator (H=–2JS1S2), giving the exchange integral J=–2.92, –3.45, –4.03 cm–1, respectively. This result indicates the presence of a weak antiferromagnetic spin exchange interaction between the metal ions.     

Effect of rigid fragments in the macrocycle on the adaptation of crown ethers to alkali-metal ions

Complexation selectivity curves were obtained by theoretical conformational analysis and penalty functions in terms of the conformational factors in the following crown ethers: 15-crown-5; benzo-15-crown-5: 18-crown-6; benzo-18-crown-6; dibenzo-18-crown-6; cyclohexano-18-crown-6. In the last case the effect of cis—trans isomerism in the bridging bonds on the selectivity of complexation with the ligand was investigated. Analysis of the selectivity curves shows that the introduction of aromatic fragments into the macrocycle reduces its adaptive capabilities. The complexation selectivity of the ligands from the selectivity curves is compared with the experimental stability series of the crown ether complexes with alkali metals.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 3, pp. 355–360, May–June, 1990.     

Reasons for increased selectivity of catalysts for partial oxidation of methane using N2O as oxidizing agent

It was found that the increase in the selectivity of catalysts of the partial oxidation of methane by nitrous oxide (compared with the oxidation by molecular oxygen) is due to the participation in the reaction of adsorbed oxygen anion radicals O^·–, with which the differences in the reactivity of methane and its mild oxidation products are leveled out. With O₂, the reactivity of methane is much lower than that of formaldehyde and methanol and, as a result, the selectivity is low, and a postoxidation of the partial oxidation products rapidly takes place. The formation of O^·– is promoted by low concentrations of metal ions in the catalyst. The influence of the geometrical factor is thus also manifested: at low concentrations of the metal ions (M), the surface postoxidation of the adsorbed formaldehyde (the nonlinear stage) is hindered, which favors increase in the selectivity with respect to HCHO.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 6, pp. 727–729, November–December, 1988.     

Oxidation of Ethylbenzene with Dioxygen in the Presence of Iron(III) Tris(acetylacetonate)-Based Catalytic Systems: 1. Mechanism of Ethylbenzene Oxidation with Dioxygen Catalyzed by Fe(III)(acac)<Subscript>3</Subscript>

The catalytic activity of Fe(III)(acac)₃ (Cat) in ethylbenzene oxidation with dioxygen is studied. 1-Phenylethyl hydroperoxide (PEHP), acetophenone (AP), and methyl phenyl carbinol (MPC) are the main products of the process throughout the Cat concentration range examined. Phenol (Ph) is formed in much smaller amounts. The highest PEHP selectivity, S _PEHP = 65%, is observed at an ethylbenzene conversion of C ≈ 2% at low [Cat] values. PEHP and the other main oxidation products (AP and MPC) form by parallel reactions at any Cat concentration. Depending on [Cat], AP and MPC form by parallel or consecutive reactions. When [Cat] is high enough, AP results from MPC oxidation. At the initial stages of the reaction, the MPC selectivity (S _MPC = 50%) exceeds the PEHP selectivity (S _PEHP = 25–30%). The mechanism of ethylbenzene oxidation catalyzed by Fe(III)(acac)₃ and the role of active complexes in its steps are considered.__________Translated from Kinetika i Kataliz, Vol. 46, No. 3, 2005, pp. 354–359.Original Russian Text Copyright © 2005 by Matienko, Mosolova.     

Kinetics of Chlorohydrination of Allyl Chloride

The chlorohydrination of allyl chloride with chlorine in water was studied at 20–80°C. The effect of the concentration of chloride ions within the range 0–3.6 mol/l on the selectivity of formation of glycerol dichlorohydrins was studied. An equation that relates the selectivity and the concentration of Cl^–was derived, which adequately describes experimental data. The schemes of parallel and consecutive reactions occurring in the system were suggested. The ratios between the rate constants of the following reactions were found: the reactions of chlorine with water and allyl chloride dissolved in water (k ₁/k ₄= 4.1 × 10^–4), the reaction of allyl chloride with hypochlorous acid and the decomposition of hypochlorous acid (k ₂/k ₃= 1.7 × 10³), and the reactions of the allyl chloride–chlorine complex with a water molecule and Cl^–(k ₅/k ₆= 2.9 × 10^–2).     

Study of the selectivity of the complexation of new aminomethyl-Phosphonic cyclopendants by theoretical conforma tional analysis

The results of a theoretical conformational analysis of two new organophosphorus chelating agents, which are derivatives of cyclic polyamines belonging to the cyclopendant class, have been presented. The study of the complexing properties with respect to transition metals and group-II metals revealed that one of the chelating agents displays high selectivity with respect to metal cations and that its analog is less selective, but forms very strong complexes with ions of heavy metals. In this context it seemed of interest to evaluate the role of the steric factor in the complexation selectivity. The calculation was carried out in the framework of the method of atom-atom potential functions. The results of the calculations were compared with experimental data on the stability of the complexes with 14 cations, and conclusions regarding the behavior of these ligands in complexation reactions have been drawn.Deceased.Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 21, No. 6, pp. 660–669, November–December, 1985.     

Conversion of ethylene to butadiene and higher hydrocarbons in the absence of a catalyst

The conversion of ethylene to butadiene and higher hydrocarbons in the absence of a catalyst in the temperature range 973–1023 K, an ethylene partial pressure of 2–15 kPa and a flow rate of 30–150 cm³/min. The effect of the reactor free space on the overall conversion of ethylene and its selectivity has been studied. The probable steps in the formation of the principal products is discussed.Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 31, No. 2, pp. 95–99, March–April, 1995.This work was carried out with a grant from the Ukraine State Committee on Science and Technology.     

Influence of the conjugate anion on the parameters of ESR spectra in radical cations of sterically hindered hydroquinones

The reactions of hindered p-quinones and hydroquinones with inorganic, organic, and Lewis acids have been studied by ESR. The conjugate anion has a strong perturbing effect on the distribution of the spin density at the reaction center. A mechanism for the reduction of p-quinones and the oxidation of hydroquinones, which includes a step involving the formation of radical-cation salts, has been proposed. The form of the ESR spectra and the composition of the final products are greatly dependent on the ratio between the reactants, the medium, and the temperature.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 6, pp. 737–741, November–December, 1986.     

Geometric and Electronic Structure of WSiN(N = 1–6, 12) Clusters

Geometry optimizations of WSi _N (n = 1–6, 12) clusters are performed using the B3LYP/ LanL2DZ method for a sequence of different spin states, changing from spin singlet to spin septet conditions. The resulting equilibrium structures are discussed under the aspects of geometric features, cluster internal charge transfer and magnetic properties. It is shown that the W impurity in the Si _N environment generally acts as an electron acceptor. However, the charge on the W atom, as obtained by natural population analysis, can be sensitively tuned through the variation of the spin constraint from S = 0 to S = 3. The resulting geometries of WSi _n (N = 3–6) are compared with the known ground state structures of Si _N+1 (N = 3–6), and substitutional geometries are identified for N = 3 and N = 5. The nonzero spin states of WSi _N are shown to display different patterns of magnetic order, corresponding to uniform and to alternating atomic spin orientations within the cluster. Highly compact O _h and D _6h structures are identified as stable geometries of WSi₆ and of the experimentally detected unit WSi₁₂, respectively. Comparison is made with the cluster series MoSi_N(N = 1–6) and CuSi _N (N = 1–6,12).     

Vibronic coupling effects in trimeric mixed-valence clusters

The spectrum of a trimeric mired-valence cluster d₁–d₁–d₂ is calculated in the Piepha-Krausz-Schatz vibronic model. Based on the vibronic spectra obtained magnetic properties of the d₁–d₁–d₂ cluster are investigated It is shown that spin of the system's ground state may change not only as a result of double exchange reduction by vibronic coupling, but also due to a diflerence in the eneqy dependence of the lowest vibronic states on the vibronic coupling constant for diflerent total spin values. Unlike previous studies of vibronic interactions in the d₁–d₁–d₂ cluster, in this study the diagonalizations of the vibronic-coupling and double-exchange matrices are fuljilled simultaneously, using Lanczos' method. Due to this, all types 4 vibronic state mixing by double exchange could be taken into account properly.Moldova State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 34, No. 5, pp. 20–32, September–October, 1993.Translated by L. Smolina