Synthesis and crystal chemistry of NH3(MoO3)3

NH₃(MoO₃)₃ crystallizes with hexagonal symmetry, space group $\text{P6}{}_3\text{m}$, lattice constants a = 10.568 Å, c = 3.726 Å, and Z = 2. The crystal structure has been determined by Patterson synthesis and refined assuming isotropic temperature factors to a final conventional R value of 0.085. The structure shows a three-dimensional arrangement built up of double chains of distorted MoO₆ octahedra, parallel to the [001] direction. The octahedral double chains are linked among each other through common oxygen atoms. In addition to the shared oxygen atoms, each molybdenum is coordinated to one terminal oxygen. MoO distances range from 1.645 to 2.378 Å and OMoO angles from 74.3 to 114.3°. These results are consistent with the fact that molybdenum in high-valence states shows octahedral coordination with terminal oxygens.     

An electrochemical study of redox indicators : Part I. Substituted chrysoidines

The electrochemical oxidation of various substituted chrysoidines was studied by cyclic voltammetry, to determine which have stable oxidation products. Only 4-hydroxy-chrysoidine has a stable product; the apparent oxidation potential is 0.779 V vs. NHE. 4-Methoxy- and 4-ethoxy-chrysoidine rapidly lose methanol or ethanol, respectively, so that the 4-hydroxychrysoidine wave appears on subsequent scans. All the other chrysoidines studied are irreversible. The results indicate that a hydroxy group in the 4-position is necessary for stability; the 4-alkoxychrysoidines can achieve the stable quinoidal structure by cleavage of the alkoxy group after nucleophilic attack.     

High-resolution photoelectron spectroscopy through deconvolution

A new iterative deconvolution algorithm for the development of very high resolution Hc(I)-excited photoelectron spectra of gases is presented. The algorithm accepts as input a medium-resolution spectrum and an instrument function obtained by scanning intrinsically narrow line (e.g. the Ar²P_3/2 line) under conditions identical to those used to acquire the medium resolution spectrum. The deconvolved partial spectrum of an O₂H₂O mixture is presented as a test case prior to presentation of results for three nitrogen lines. For comparison purposes directly obtained high-resolution spectra of the nitrogen lines are included. The shapes of the nitrogen lines are discussed within the framework of a one-center expansion theory of photoionization. The conditions under which deconvolution can be profitably applied are briefly discussed and an attempt is made to establish the deconvolution (contrary to still popular belief) is not in any way equivalent to curve fitting.     

Stereochemistry of cyclic ether formation—II : Intramolecular cyclisation of secondary aliphatic alcohols to tetrahydrofuran-type ethers

The mechanism and stereochemistry of δ-C atom functionalisation in the reactions of secondary straight-chain aliphatic alcohols with lead tetraacetate, ceric ammonium nitrate, and heavy metal (Pb⁴⁺, Hg²⁺, Ag⁺) salts (AcO)^?1, O^2?, CO₃^2?-halogen (I₂, Br₂, Cl₂) combinations are discussed. By demonstrating the intermediacy of 5-bromo-2-hexanol, it was confirmed that the dark silver oxidebromine induced cyclisation of 2-hexanol (and alcohols in general) involves (as the other hypohalite reactions) intramolecular 1,5-hydrogen abstraction by alkoxy radicals and formation of δ-bromohydrins. A novel and simple procedure for obtaining tetrahydrofurans from alcohols by way of the hypochlorite reaction, using silver or mercuric salts and chlorine, is described.     

Preparation and structure of fluorite-type (Sr,Y)Cl2.05

Anion excess colorless fluorite-type strontium-yttrium chloride has been prepared. Single crystals of the SrY compound exhibit a primitive cubic lattice with a = 6.967(1)Å. Two mutually exclusive structural models for solutions, neither of which is exact, are discussed. The first is a vacancy model in which the extra charge which results from substitution of Y³⁺ for Sr²⁺ is balanced by the simultaneous removal of a Sr²⁺Cl^? ion pair. This model requires individual ion sites to be partially occupied and nonequivalent and is strongly suggestive of vacancy ordering. Refinement in space group P1, with sites refined independenty, led to R = 0.1096. The second model describes the structure in terms of a Willis cluster of defects and includes both anion vacancies and interstitial anions. Full-matrix least squares refinement in space group Fm3m, with positions analogous to those in UO_2.12 and (Ca,Y)F_2.10, converged at R = 0.0633 for the 114 face-centered parent structure reflections whose |F|;² > σ(F²). This second model is discussed in relation to a probable true solution which involves longrange order.     

Photochemistry of iminium salts : Electron transfer mechanisms for singlet quenching and photoaddition of n-electron donating alcohols and ethers

Several aspects of past and current studies in the area of iminium salt photochemistry are discussed. Investigations of olefin-iminium salt photoaddition and photocyclization reactions are reviewed and conclusions about electron-transfer pathways for fluorescence quenching and reaction are discussed. The results of recent studies of alcohol and ether photoaddition to 2-phenyl-1-pyrrolinium salts are presented. These C-C bond forming processes occur in moderate yields to produce β-amino alcohol or ether products. In addition, alcohols and ethers serve as efficient quenchers of pyrrolinium salt fluorescence. Rate constants for quenching appear to be dependent upon both the oxidation potential of the alcohols and ethers and the availability of C-H bond α to oxygen. This data along with deuterium isotope effects on quenching combine to suggest a common mechanism for both fluorescence quenching and photoaddition. The nature of this mechanism is tested using the comparative quenching effeciencies of the tertiary alcohols t-butyl alcohol and 1,2,2-trimethyl-1-cyclopropanol. The latter alcohol having a weak C-C bond adjacent to the hydroxyl function quenches the fluorescence of 2-phenyl-1-pyrrolium salts at a rate two orders of magnitude greater than for t-butyl alcohol. The observations made are interpreted in terms of a sequential electron-proton transfer mechanism for quenching and photoaddition. Lastly, the relationship of iminium salt photochemical studies to other investigations of electron-transfer photochemistry is discussed.     

Thermodynamics of solvent extraction of thorium by solutions of HHTA and mixtures of HHTA and TBP

The changes in free energy, enthalpy and entropy for the extraction of thorium by solutions of thenoyltrifluoroacetone (HTTA) and mixtures of solutions of HTTA and tri-n-butylphosphate (TBP), in three diluents, viz. cyclohexane, benzene and chloroform, were determined using the solvent extraction data obtained at different temperatures. From these data the thermodynamic parameters associated with the formation of Th(TTA)₄ · TBP in the respective organic diluents were evaluated. Trends in the enthalpy changes were attributed to different degrees of association of the diluents with themselves and with the solutes present in them.     

Voltammetry at partially covered electrodes: Part I. Chronopotentiometry and chronoamperometry at model electrodes

Equations for chronopotentiometry and chronoamperometry at partially covered electrodes have been derived using a model of hexagonal array of cylidrical spaces terminated, at the electrode surface, by concentric active and inactive regions. The boundary value problem was shown to be analogous to that for a charge transfer preceded by a chemical reaction. Experiments with the reduction of ferricyanide on gold model electrodes partially covered with photoresist layer showed excellent agreement with the theory. Application of the equations to estimation of coverage and size of active sites distributed on a electrode surface is discussed.     

Photochlorination of tetramethylsilane and hexamethyldisilane in the gas phase

Preliminary studies of the reaction of chlorine with tetramethylsilane and hexamethyldisilane in the gas phase show that the photochlorination of tetramethylsilane is complex, giving different products from the corresponding reaction in solution and having an explosion boundary. At pressures below the explosion boundary the main products are ethylene, hydrogen chloride, dimethylchlorosilane, and more highly chlorinated methylsilanes. Above the explosion boundary main products after explosion are methane, acetylene, ethylene, hydrogen chloride, and silicon tetrachloride. Hexamethyldisilane reacts rapidly with chlorine in the dark, as it does in solution, forming mainly trimethylchlorosilane along with similar products to those found with tetramethylsilane. Subsequent photochlorination of trimethylchlorosilane follows a similar course to that of tetramethylsilane in the gas phase. Tentative mechanisms involving “hot” molecules are suggested.     

Vinylidene complexes of transition metals : III. Derivatives of cyclopentadienyltricarbonyl rhenium with phenylvinylidene ligands. Crystal and molecular structure of Cp(CO)2Re[CC(Ph)C(Ph)CH2]Re(CO)2Cp

The novel complexes CpRe(CCHPh)(CO)₂ and Cp₂Re₂(μ-CCHPh)(CO)₄ containing a terminal and a bridging phenylvinylidene ligand respectively and the binuclear complex Cp(CO)₂Re[CC(Ph)C(Ph)CH₂]Re(CO)₂Cp were obtained in the reaction of CpRe(CO)₃ with PhCCH.According to an X-ray study of the latter complex the unusual bridging ligand is η¹-bonded to one Re atom and η²-bonded to the other.