Raman spectra of the polymeric difluorides of the group IV elements and the structure of polydifluorosilylene

The Raman spectra for (SiF₂)_x and GeF₂ are reported. In the spectrum of (SiF₂)_x a band has been observed at 411 cm⁻¹ and is most probably associated with SiSi bonding in the compound; this is the first direct evidence for such a bond. The high degree of similarity between the spectra of (SiF₂)_x and (CF₂)_x suggests that (SiF₂)_x is a zig-zag helical chain polymer similar to (CF₂)_x.     

Change in the mechanism of the electroreduction of the perfluoro-n-hexyl iodide with varying the nature of the supporting salt Application to electrocarboxylation and sulfoxidation

We have previously reported that reduction of C₆F₁₃I in (DMF, LiClO₄), yields R_FHgR_F, produced through the reduction of R_FHgI itself formed at polarized mercury. The use of LiCl in the place of LiClO₄ affords a possibility to suppress the organometallic route and yields the carbanion C₆F₁₃, formed through a direct bielectronic reduction. This feature is exploited to perform electrocarboxylation and sulfoxidation. In this way, R_FCO₂H and R_FSO₂Cl are easily electrosynthesized in macroscale experiments. The anion effect remarked between Cl^? and ClO₄^? is studied in the case of Br^?, I^?, BF₄^? with various cations.     

Effect of the nature of the salt precursor of an oxide-hydroxide sorbent on the sorption of oxalate ions

Generalizations are made on the effect of the nature of a precursor (the original salt of a metal) on the sorption activity of hydrogels of oxidehydroxides (OHes) towards oxalate ions using the example of an OH obtained by the alkaline hydrolysis of chloride, perchlorate, and sulfate of Fe(III); chloride, sulfate, and nitrate of Al; and nitrate of Zr(IV). It is established that the sorption of C₂O ₄ ^2? on the studied OHes is described by the Langmuir equation. We find that the sorption activity depends on the nature of the precursor: Al₂(SO₄)₃ > Al(NO₃)₃ > AlCl₃ > ZrO(NO₃)₂ > Fe₂(SO₄)₃ > FeCl₃ > Fe(ClO₄)₃.     

Effect of desolvation of the reactants during change in the acidity of the medium on the electrophilic hydroxylation and nitration of alkanes

The effect of the acidity of the medium on the hydroxylation and nitration of alkanes (RH) in 90–98% H₂SO₄ at 25°C is described quantitatively by a model taking account of the thermodynamic activity of the RH, H₂O, and HSO₄^- particles. It was concluded that in the transition states the reagents H₃O₂⁺HSO₄^- and NO₂⁺ HSO₄^- are present as HO⁺ and NO₂⁺ ions without the bases H–O and HSO₄^-, the alkanes are present without hydrophobic shells, and the initial reaction products are ROH₂⁺ and RNO₂H⁺.     

On the mechanism of the reduction of molecular nitrogen with aryldicyclopentadienyltitanium(III) complexes

The first step in the reduction of the dinitrogen ligand in (Cp₂TiR)₂N₂ (R  C₆H₅, m-, p-CH₃C₆H₄, C₆F₅, CH₂C₆H₅) by sodium napthalene (NaC₁₀H₈) involves the removal of one Cp group per titanium atom. The resulting diimide precursor reacts with a second mole of NaC₁₀H₈ with formation of a hydrazine precursor. This compound is thermally unstable and decomposes to an ammonia precursor. A minor part of the hydrazine precursor abstracts a proton from the solvent.     

Effect of the nature of the anion on the composition and structure of cobalt complex with monoethanolamine

A number of products formed in reactions of cobalt(II) salts with monoethanolamine (HEtm) in a neutral medium were synthesized and studied. X-Ray diffraction study showed that the nitrate and acetate form the dimers [Co(HEtm)₃][Co(Etm)₃](NO₃)₃ and [Co(HEtm)₃][Co(Etm)₃](CH₃COO)₃ · 8H₂O, respectively. In chloride solutions, cobalt is partially oxidized to give the trinuclear complex [Co^II{Co^III(Etm)₃}₂]Cl₃ · H₂Etm · 2H₂O. The reaction of the chelate [Co(Etm)₃] · 3H₂O with nitric acid is accompanied by complete protonation of the coordinated aminoethanolate ions, and the reaction with formic acid involves complete replacement of the coordinated ligand by acid residue anions and water molecules to give the coordination polymer {Co₂(μ-HCOO)₄(H₂O)₄} _n .     

Perfluoropolyether alkyl diesters: Structure effects of the alkyl group on the kinetics of the hydrolysis reactions

A series of perfluoropolyether bis‐carboxylic esters was synthesized and their hydrolytic stability investigated. Their formula is ROOCCF₂O(CF₂CF₂O)_p(CF₂O)_qCF₂COOR, where p/q = 1.07 and p + q = 2.94. The alkyl group, R, varied both in terms of steric hindrance and electron‐withdrawing ability. Kinetic and thermodynamic data were obtained under homogeneous conditions and compared to a fully hydrogenated ester having a closely related structure CH₃(CH₂)₃OOCCH₂O(CH₂CH₂O)_nCH₂COO(CH₂)₃CH₃, where n? = 10.6. Neutral ester hydrolysis (NEH) conditions were selected with methyl ethyl ketone as a solvent and a 3–4:1 water/ester ratio. The course of the reaction was monitored by ¹⁹F NMR or ¹H NMR (when R = CH₃CH₂? ). Results indicated that the hydrolysis of fluorinated esters, with alkyl aliphatic substituents, is governed by steric hindrance of the substituents. Two distinctive kinetic regimes were observed. The first one, at low conversion, was characterized by lower kinetic constants and related to true NEH conditions. The second regime appeared at higher conversion when acidic autocatalysis dictated the reaction behavior. This is the only observed mechanism when esters more sensitive to the hydrolysis are considered. In these cases, polar factors prevail over steric considerations. Finally, all fluorinated esters of the class (I) showed a much higher reactivity than the hydrogenated ester whose hydrolysis took place only in the presence of a strong acidic catalyst. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4266–4280, 2002     

On the minimization of the global variance in the 1-Reduced local-energy matrix

By minimizing the global variance in the 1-reduced local-energy matrix E₁( X ₁; X ₁′), subject to the normalization of the 1-reduced density matrix ρ₁( X ₁; X ₁′), one derives an integral matrix equation for E₁( X ₁; X ₁′) as a functional of ρ₁( X ₁; X ₁′) at the location ( X ₁; X ₁′) of an arbitrary member of an N (≥ 2)-particle system. The implications for the possible local improvement in the accuracy of approximate wave functions through the imposition of global constraints are briefly discussed.     

Jahn—Teller effects in the mindo approximation: structures of the molecular cations of methane and the chloromethanes

The MINDO/3 technique gives geometries for (CH₄)⁺, (CCl₄)⁺ and the intermediate ions (CH_nCl_{4 ? n})⁺ (n = 1, 2, 3) which have symmetries in precise accord with the predictions of the Jahn—Teller effect. The ground state of (CH₄)⁺ has D_2d symmetry, with a C_3v structure ca. 45.6 kJ mol^?1 higher. (CCl₄)⁺ has a C_2v ground state, with a D_2d structure ca. 144 kJ mol^?1 higher: no bound state of C_3v symmetry could be found. (CH₃Cl)⁺ and (CHCl₃)⁺ both have C_s symmetry, and (CH₂Cl₂)⁺ has C_2v symmetry. The analogous fluoro ions are discussed briefly.     

Investigation of the initial reactions of the Calcote mechanism for soot formation

The first three reactions of the Calcote mechanism for soot formation, that is, C₃H ₃ ⁺ +C₂H₂→C₅H ₅ ⁺ , C₅H ₅ ⁺ →C₅H ₃ ⁺ H₂, and C₅H ₃ ⁺ +C₂H₂→C₇H ₅ ⁺ , have been studied based on chemi-ions withdrawn directly from a premixed methane-oxygen flame by supersonic molecular beam sampling. The first reaction is reversible and involves the formation of a specific encounter complex sensitive to pressure and ion kinetic energy. The second reaction appears to require large amounts of internal energy in the C₅H ₅ ⁺ ion to proceed. The third reaction is reversible; however, in contrast to the initiating reaction, the C₅H ₃ ⁺ ion formed from the [C₇H ₅ ⁺ ]* complex exhibits a much lower reactivity. The conclusions are based on ion-molecule reactions as well as collision activation mass spectrometry of isolated chemi-ions. In addition, the product distributions as functions of pressure and ion kinetic energy were studied.     

On the optimal mixing of the exchange energy and the electron-electron interaction part of the exchange-correlation energy

The optimal mixing coefficient C of the exchange energy E_x and the electron-electron interaction part of the exchange-correlation energy W¹_xc in the formula for the total exchange-correlation energy E_xc was expressed through the ratio of the kinetic T_c and potential W_c contributions to the correlation energy E_c. This expression can be derived from a Heavyside step function model of the dependence of W^λ_xc on the coupling parameter of the electron interaction λ. Values of T_c and W_c obtained from ab initio wave functions were used to estimate C for a number of atoms and molecules. A strong dependence of T_c, W_c, and C on the bond distance was demonstrated for the case of the H₂ molecule. T_c and C approach zero in the bond-dissociation limit; so for an electron-pair bond, the admixing of exact exchange to obtain an accurate E_xc is strongly dependent on the bond length and has to disappear for weak interaction/large bond distances. The potential of the exchange-correlation hole constructed for H₂ from an ab initio second-order density matrix was compared with its generalized gradient approximation (GGA). © 1996 John Wiley & Sons, Inc.     

Quantum-chemical study of the effect of oxygen on the formation of active sites of silver clusters during the selective adsorption of hydrocarbons

Density functional theory (PBE with a modified Dirac-Coulomb-Breit Hamiltonian) is used to simulate the adsorption of hydrocarbons (C₂H₂, C₂H₄, C₂H₆) on the surface of a sorbent containing Ag⁰, Ag^δ+, and AgO sites. The dynamics of change in the structural characteristics of Ag _n (n ≤ 10) is analyzed and the adsorption of oxygen on Ag₈ and Ag₁₀ is studied to select the adsorption site model. Studying the interaction of hydrocarbons with Ag₈, Ag₁₀, Ag ₁₀ ⁺ , Ag₁₀O, and Ag₁₀O₂ clusters reveals that the presence of oxygen leads to an increase in the activation of unsaturated hydrocarbons, and the adsorption energy of C₂H₂ increases tenfold. It is found that the role of adsorbed oxygen is not only to form adsorption sites of hydrocarbons (Ag^δ+) but also to bind C₂H₂ and C₂H₄ directly to the sorbent’s surface.     

Assessing the Viability of the Methylsulfinyl Radical-Ozone Reaction

Although integral to remote marine atmospheric sulfur chemistry, the reaction between methylsulfinyl radical (CH₃SO) and ozone poses challenges to theoretical treatments. The lone theoretical study on this reaction reported an unphysically large barrier of 66 kcal mol⁻¹ for abstraction of an oxygen atom from O₃ by CH₃SO. Herein, we demonstrate that this result stems from improper use of MP2 with a single-reference, unrestricted Hartree-Fock (UHF) wavefunction. We characterized the potential energy surface using density functional theory (DFT), as well as multireference methodologies employing a complete active-space self-consistent field (CASSCF) reference. Our DFT PES shows, in contrast to previous work, that the reaction proceeds by forming an addition adduct [CH₃S(O₃)O] in a deep potential well of 37 kcal mol⁻¹. An O−O bond of this adduct dissociates via a flat, low barrier of 1 kcal mol⁻¹ to give CH₃SO₂+O₂. The multireference computations show that the initial addition of CH₃SO+O₃ is barrierless. These results provide a more physically intuitive and accurate picture of this reaction than the previous theoretical study. In addition, our results imply that the CH₃SO₂ formed in this reaction can readily decompose to give SO₂ as a major product, in alignment with the literature on CH₃SO reactions.     

Phase relations up to the solidus line in the part of the Sb-Zn-O system

Phase relations up to the solidus line in part of the Sb-Zn-O system have been investigated over the entire concentration range of the α-Sb₂O₄-ZnO system in air (= 0.21 atm) using XRD and DTA/TG. The components of this system in air form ZnSb₂O₆ and Zn₇Sb₂O₁₂. The results allow division of the system into three subsystems, i.e. α-Sb₂O₄-ZnSb₂O₆; ZnSb₂O₆Zn₇Sb₂O₁₂ and Zn₇Sb₂O₁₂-ZnO. The temperature ranges over which the ZnSb₂O₆ and Zn₇Sb₂O₁₂ remain at equilibrium with other solid compounds depend on the gaseous atmosphere.      

Investigation of the electronic structures of vinyl silicon compounds by the free electron method

The two compounds, Me₄Si₂ (C₂H₃)₂ and Me₈Si₂ (C₂H₃)₂ have been studied by the anti-symmetrized free electron molecular orbital method. Electron delocalisation over the whole chain via the silicon atoms occurs and a satisfactory account of the electronic spectra may be obtained.

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Zusammenfassung Me₄Si₂ (C₂H₃)₂ und Me₈Si₄ (C₂H₃)₂ wurden nach der MO-Methode des freien Elektronengases behandelt. Delokalisierung der Elektronen über die Si-Atome der Kette wird festgestellt. Die berechneten Spektren sind zufriedenstellend.

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Résumé On a étudié par la méthode des orbitales moléculaires d'électrons libres avec antisymétrisation les composés Me₄Si₂(C₂H₃)₂ et Me₈Si₄(C₂H₃)₂. Il se produit une délocalisation électronique le long de toute la chaÎne par l'intermédiaire des atomes de silicium, et l'on peut rendre compte d'une manière satisfaisante des spectres électroniques.

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We wish to thank the S.R.C. for a maintenance grant to one of us (D.R.A.).     

Mechanism of the decomposition of the surface oxide film on polycrystalline palladium

The decomposition of thin surface oxide films on polycrystalline palladium Pd(poly) at 500–1300 K was investigated by mathematical modeling. This process was analyzed in terms of a model including O₂ desorption from the chemisorbed oxygen layer (O_ads) and the passage of oxygen inserted under the surface layer of the metal (O_abs) and oxygen dissolved in metal subsurface layers (O_dis) to the surface. O₂ desorption was modeled on a surface with a square lattice of adsorption sites, with account taken of the energy of the lateral repulsive interactions between adjacent O_ads atoms (ε_aa). At ε_aa = 10 kJ/mol and when the activation energy of O₂ desorption for a chemisorbed-oxygen surface coverage of θ ≈ 0 is E_des⁰ = 230 kJ/mol, the calculated spectra are in agreement with the oxygen temperature-programmed desorption (TPD) spectra obtained for Pd(poly) at θ ≤ 0.5. The passage of O_abs and O_dis atoms to the surface was calculated using a first-order equation, with account taken of the activation energy for these atoms coming out to the surface (E₂ and E₃, respectively). As the oxide film is heated, O₂ desorption is accompanied by the passage of O_abs and then O_dis to the surface, which leads to an increase in the O_ads surface coverage and, accordingly, to a buildup of lateral surroundings in the adsorbed layer. Owing to this fact and to the repulsive interactions between O_ads atoms, the bonds between O_ads and the surface weaken and E_des decreases. As a consequence, the O₂ desorption rate increases and a low-temperature peak with T_max ≈ 710 K, which is due to the passage of O_abs atoms to the surface, and then a high-temperature peak with T_max ≈ 770 K, which is due to the passage of O_dis atoms to the surface, appear in the TPD spectrum. At ε_aa = 10 kJ/mol, E_des⁰ = 230 kJ/mol, E₂ = 145 kJ/mol, and E₃ = 160 kJ/mol and when the number of inserted oxygen monolayers is θ_abs ≤ 0.3 and the number of oxygen monolayers dissolved in subsurface layers is θ_dis ≤ 10, the TPD spectra calculated for the given model are in agreement with the O₂ TPD spectra that are observed for Pd(poly) and are due to the decomposition of surface oxide films.     

Assignment of the mechanism of predissociation of the ClO2 molecule by analysis of single-rotational-level lifetimes

Deconvolutions of measured absorption line profiles in the 1ⁿ₀ (n = 0 to 5) and the 3²₀ bands of the òA₂X?²B₁ electronic transition of ClO₂ reveal subnanosecond lifetimes for all rotational levels of the ²A₂ state. Observed ratios of radiationless rates from spin-doublet components identify direct spin-orbit coupling of the ²A₂ state with ²A₁ and/or ²B₁ vibronic states as a predominant predissociation mechanism. Variations of rates with ν′₁ locate an intersection of a second potential surface with that of the ²A₂ state.     

Variable hapticity of the cyclooctatetraene ring in sandwich compounds of the first row transition metals

Density functional theory methods (B3LYP and BP86) indicate that the preferred structures for such early transition metal derivatives are (η⁸-C₈H₈)M(η⁴-C₈H₈) (M = Ti, V, Cr) with one octahapto η⁸-C₈H₈ ring and one tetrahapto η⁴-C₈H₈ ring. In such structures only 12 of the 16 carbon atoms of the two C₈H₈ rings are bonded to the metal, leading to 16-, 17-, and 18-electron complexes, respectively, in accord with the experimentally known structures for the Ti and V derivatives. The preferred structures for the Mn and Fe derivatives are (η⁶-C₈H₈)M(η⁴-C₈H₈) (M = Mn, Fe) with one hexahapto and one tetrahapto C₈H₈ ring and thus having 17- and 18-electron configurations, respectively, in accord with experimental data on the iron complex. The lowest energy structure for the cobalt complex is (η⁴-C₈H₈)Co(η^2,2-C₈H₈) with two different types of tetrahapto C₈H₈ rings and a 17-electron metal configuration. The nickel complex (C₈H₈)₂Ni appears to prefer a structure with a 16-electron configuration and two trihapto C₈H₈ rings, similar to the known (η³-C₃H₅)₂Ni rather than a bis(tetrahapto) structure with the favored 18-electron configuration. These theoretical studies indicate that in (C₈H₈)₂M derivatives of the first row transition metals, the number of carbon atoms in the pair of C₈H₈ rings involved in the bonding to the central metal atom gives the metal atoms 16-, 17-, or 18-electron configurations.     

Features of the mass-spectrometric fragmentation of the teucrins H

Summary Characteristic directions of the mass-spectrometric fragmentation of teucrins H are the elimination of -vinylfuran and a carboxy group, and also the formation of furan-containing ions with the compositions C₁₁H₁₂O₃ (m/e 192), C₁₀H₁₀O₃ (m/e 178), C₁₁H₁₁O₂ (m/e 175), C₁₁H₁₀O₂; (m/e 174), C₁₀H₉O₂ (m/e 161), C₁₀H₈O₂ (m/e 160), C₉H₁₀O₂ (m/e 150), C₁₀H₁₁O (m/e 147), C₉H₉O (m/e 133), C₆H₇O (m/e 95), C₆H₆O (m/e 94) CsHzO (m/e 81).Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 727–736, November-December, 1978. Original article submitted May 3, 1978.     

A theoretical study of the bonding capabilities of the zinc-zinc double bond

The theoretical knowledge about the zinc-zinc bond has been recently expanded after the proposal of a zinc-zinc double bond in several [Zn₂(L)₄] compounds (Angew. Chem. Int. Ed. 2017 , 56, 10151-10155). Prompted by these results, we have selected the [Zn₂(CO)₄] species, isolobally related to ethylene, and theoretically investigated the possible η²-Zn₂-coordination to several first-row transition metal fragments. The [Zn₂(CO)₄] coordination to the metal fragment produces an elongation of the dizinc bond and a concomitant pyramidalization of the [Zn(CO)₂] unit. These structural parameters are indicative of π-backdonation from the metal to the coordinated dizinc moiety, as occurred with ethylene ligand. A quantum theory of atoms in molecules study of the Zn Zn bond shows a decrease of ρ_BCP, ∇²ρ_BCP ∫_Zn∩Znρ and delocalization indexes δ(Zn,Zn), relative to corresponding values in the parent [Zn₂(CO)₄] molecule. The Zn Zn and M Zn bonds in these [(η²-Zn₂(CO)₄)M(L)_n] complexes can be described as shared interactions with an important covalent component where the Zn Zn bond is preserved, albeit weakened, upon coordination.