J. Barrie Raynor

Reliability of experimental partition coefficients in carbonate systems: Evidence for inhomogeneous distribution of impurity cations

Abstract Electron spin resonance (ESR) spectroscopy, thermal analysis and X-ray diffraction (XRD) analysis are used to study the mode of incorporation of a wide range of impurity ions (up to 1% Ni 2+ , Sr 2+ , Cd 2+ , Mg 2+ , Cu 2+ , Fe 2+ , Zn 2+ , Pb 2+ , Mn 2+ and Ba 2+ ) in calcites synthesised in aqueous solutions. It is shown that when certain impurity ions are incorporated in these calcites they become concentrated, together with other trace elements such as Mn 2+ , into hitherto unsuspected trace phases. The important conclusion is drawn that unless the scavenging of trace elements by these phases can be avoided or corrected for, any calcite—liquid partition coefficients measured may have limited significance. ESR spectroscopy has revealed the intense strain common in calcites grown by different methods, whilst thermal analysis suggested that such strain may significantly alter the thermodynamic properties of these calcites. ESR spectroscopic analysis of aragonites synthesised by methods previously reported in the literature has revealed the common occurrence of trace calcite at concentrations below the XRD detection limit and proves the tendency of this calcite to scavenge trace Mn. Using ESR spectroscopy to monitor trace calcite levels and structural imperfections in synthetic aragonites, the urea hydrolysis technique is modified to provide a method for the synthesis of high-purity strain-free aragonite available for experimental studies.

The copper-molybdenum antagonism in ruminants. III. Reaction of copper(II) with tetrathiomolybdate(VI)

Abstract The stoichiometry of the reaction between Cu(II) and MoS42− in neutral aqueous solution was observed to proceed with a 1.5:1 Cu:Mo ratio. The reaction results in the reduction of Cu(II) and the quantitative formation of an insoluble solid. The results contrast with an earlier report of a 1:1 stoichiometric ratio, this latter ratio was, however, observed with CuII(albumin) as reactant, in this case no precipitate was observed. The insoluble products were examined by a number of spectroscopic techniques and by X-ray power diffraction and elemental analysis. Two products were identified. Solid A is isostructural with the known (NH4)CuIMoVVIS4, i.e. has the composition MICuMoS4, MI= NH4+, Na+ or Et4N+. Solid B has the approximate composition CuMoS4Ox, x=2−3 and contains Cu(I) and Mo(V) centres. Formation of compound B therefore involves an unusual internal two-electron redox process. The reaction and products are of particular biological significance.

Preparation and characterization of tetrakis(tricarbonyldifluororuthenium), tricarbonyltrifluororuthenium, and bis(tricarbonyldifluororuthenium–ruthenium pentafluoride)

The ruthenium carbonyl fluorides, [{Ru(CO)3F2}4], [Ru(CO)3F3], and [{Ru(CO)3F2·RuF5}2] have been prepared in high yield. I.r. spectroscopy, magnetic susceptibility, and e.s.r. spectroscopy have shown that [Ru(CO)3F3] is monomeric but that the structure of [{Ru(CO)3F2·RuF5}2] is closely related to that of [{Ru(CO)3F2}4] and (RuF5)4, which have been previously characterized by single-crystal X-ray diffraction as fluorine-bridged tetramers.

Electron spin resonance spectra of trigonal-prismatic bis[pentane-2,4-dione benzoylhydrazonato(2—)]vanadium(IV) and bis[4-phenylbutane-2,4-dione benzoylhydrazonato(2—)]vanadium(IV)

The e.s.r. spectra of the trigonal-prismatic title complexes have been recorded. The spectra show axial symmetry and are characterised by g∥= 2.00 and g⊥= 1.956 and g∥= 2.00 and g⊥= 1.971 respectively. Analysis of the values of the hyperfine coupling to vanadium, namely A∥= 22 G and A⊥= 138 G, indicates that the unpaired electron is mainly (92 and 95%) in a metal dz2 orbital. On addition of acids the complexes decompose to [VO]2+ions.

Electron spin resonance spectroscopy of Mn(CO)5 · radicals generated in the gas phase thermolysis of Mn2(CO)10

Abstract The Mn(CO)5 · radicals from the gas-phase thermolysis of Mn2(CO)10 were trapped in a co-condensed adamantane matrix at 77 K and shown to give an ESR spectrum not contaminated by signals from other paramagnetic species. The radicals were formed in a narrow range of temperatures, 342–388 K, with an optimum at 363 K. They were found to be thermally stable, and the strongly anisotropic ESR spectrum suggested that they were fixed without free rotational movement up to 213 K. The peroxo radical Mn(CO)5O2 ·was trapped, either alone or together with Mn(CO)5·, in the presence of trace amounts of dioxygen.

Dolomite thermometry by electron spin resonance spectroscopy

Abstract Electron spin resonance (ESR) spectroscopy has been used to distinguish different genetic types of dolomite in the complex metamorphic terrain of the Ballachullish area of NW Scotland. By measuring the ESR signals of Mn2+ from the two inequivalent sites in dolomite, the partition coefficient can be determined and related to temperature. A systematic one hundred fold increase in the partition coefficient from the highest grade of contact metamorphic skarn to supergene dolomites was found. The use of this partition coefficient complements fluid inclusion and gross chemical data and is a useful aid in geothermometry.

Structural relationships derived from the analysis of electron spin resonance spectra of some technetium complexes

Abstract An extension of a method relating chemical structure to the ESR parameters A ⊥ and g ⊥ of paramagnetic technetium complexes is presented. Complexes having the same axial ligand lie in a narrow band of values of A ⊥ and g ⊥ such that Tc(II) nitrosyl and thionitrosyl complexes have distinctly different ESR parameters to Tc(VI) nitrido and oxo complexes. Thus the ESR spectrum of a solution resulting from a reaction where the nature of the product is in some doubt can be used to identify the oxidation state, the nature of the axial ligand and possible equatorial ligands.

Characterization of doped polypyrroles by mass spectrometry

Abstract The technique of mass spectroscopy has been used to identify new polypyrroles made with [(C 6 H 4 Cl) 4 B] − , [ICl 4 ] − and [Br 3 ] − counter anions. Mass spectroscopy confirms the presence of Cl − , Br − , I − , (SO 4 ) 2− , (HSO 4 ) − , (FeCl 4 ) − , (PF 6 ) − and (ClO 4 ) − as counter anions in other polypyrroles.

σ*-Radicals R3N — hal: electron paramagnetic resonance studies of the radiolysis of alkylammonium halides

Exposure of various ammonium and alkylammonium salts to 60Co γ-rays at 77 K gives a range of paramagnetic products including several R3N [graphic omitted] hal radicals (R = H, alkyl; hal = Cl, Br, l) characterised by their EPR spectra. These showed large hyperfine couplings to 14N and to halogen nuclei, indicating that they are genuine neutral radicals whose SOMO comprises, primarily, σ-orbitals from N and hal. Hence these species can be classified as σ* radicals. The stability of these R3N [graphic omitted] hal radicals is contrasted with the instability of the isoelectronic R3C [graphic omitted] hal– radical-anions, which normally have no significant lifetime, but dissociate directly to give R3C˙ radicals sometimes weakly associated with the ejected halide ions. Proton and 14N hyperfine coupling constants show that the R3N— moieties in these σ* radicals are pyramidal, in contrast with the parent amminium cations, R3N˙+ which are planar. The extent of deviation from planarity increased on going from —Cl to —l, as does the extent of delocalisation onto halogen. For the iodide complexes, the spin density on iodine decreases from ca. 70% to ca. 40% on going from the NH3 derivative to the Et3N derivative. A range of other radicals, also detected in the irradiated salts, are briefly described.

The Kinetics and Mechanism of the Pyrolysis of Manganese and Manganese Silicide CVD Precursors

The gas-phase pyrolysis of methyl pentacarbonyl manganese and acetyl pentacarbonyl manganese, both alone and in the presence of trimethyl silane, has been investigated using stirred flow reactor kinetic measurements and IR laser powered pyrolysis, together with electron spin resonance (ESR) detection of radical intermediates. For methyl pentacarbonyl manganese alone, all observations support a mechanism initiated by methyl–manganese bond homolysis, whereas the initial step in the acetyl compound involves CO loss and methyl migration. The addition of trimethylsilane sensitizes decomposition of MeMn(CO)5, yielding methane and trimethylsilyl pentacarbonyl manganese; on the other hand, Me3SiH has little effect on the rate of decomposition of MeCOMn(CO)5. A mechanism based on methyl migration is proposed to account for these observations.