Mass spectra of organometallic compounds—VIII. Some transition metal organometallic halide derivatives

The positive ion mass spectra of the transition metal organometallic halide derivatives C₅H₅M(CO)₃Cl(M ? Mo or W), C₇H₇W(CO)₂I, C₃H₅Fe(CO)₃I, [C₃H₅PdCl]₂, and [C₅H₅Mo(NO)I₂]₂ have been investigated. Further examples of the elimination of CO and C₂H₂ fragments were noted. In addition the following effects of particular interest were observed: (i) Evidence in the mass spectra of the chlorides for reactions with adventitious iodine and even bromine present in the mass spectrometer; (ii) Evidence for conversion of the compounds C₅H₅Mo(CO)₃X to the new halides [C₅H₅Mo(CO)X]₂ upon pyrolysis; (iii) Evidence for facile losses of the π-allyl group, the iodine atom, and methyl iodide in the mass spectrum of the π-allyl derivative C₃H₅Fe(CO)₃I; (iv) Evidence for loss of iodine upon introducing [C₅H₅Mo(NO)I₂]₂ into the mass spectrometer to give ions derived from [C₅H₅Mo(NO)I]₂.     

Electron-impact studies of organometallic molecules—VIII: Some transition metal derivatives of polyfluorobenzenes

The mass spectra of (π-C₅H₅)₂Ti(C₆F₅)X (X ? Cl and C₆F₅), C₆F₅Re(CO)₅, R_fFe(CO)₂(π-C₅H₅) (R_f ? C₆F₅, 4-HC₆F₄, and three isomeric H₂C₆F₃), and C₆F₅Ru(CO)₂(π-C₅H₅) are compared to those of C₆F₅X (X ? F, Cl, Br, I) and the three isomers of C₆F₄H₂. Significant differences occur, apparently depending on the relative thermodynamic stabilities of the various fragments which may be formed. Comparison of the mass spectra of pentafluorophenyl- and pentafluorobicyclo[2.2.0]hexa-2,5-dien-2-yl-Re(CO)₅ show that similar ions are produced by both complexes, perhaps because of thermal isomerisation before ionisation.     

The electronic structure of molecules by a many-body approach

The vertical valence ionization potentials of cyclopropane, ethylene oxide and ethylene imine are calculated by a many-body Green's function method. For C₃H₆ the ordering of the ionization potentials is 2e(), 1e(), 2a₁(), 1a₂(), 1e(). The assignment of the 2a₁ and the 1a₂ ionization potentials which has been controversial is thus clarified. The ordering is in agreement with the result obtained via Koopmans' theorem. For ethylene oxide and ethylene imine Koopmans' theorem fails in predicting the correct order of ionic states. For C₂H₄O the ordering of the ionization potentials is 2b ₁(), 4a ₁, 1a ₂(), 2b ₂,3a ₁, 1b ₁(), 1b ₂, 2a ₁ and for C₂H₅N 6a, 5a, 3a, 2a, 4a, 3a, 1a, 2a. The agreement of the computed ionization potentials with the experimental values is very satisfactory.     

Metal formyl complexes. Hydride transfer to group VIII transition metal carbonyl clusters

The reaction of LiBH(C₂H₅)₃ with Os₃(CO)₁₂ or Ir₄(CO)₁₂ leads to the formation of spectroscopically detectable formyl complexes. In the latter case, the complex is smoothly converted to [Ir₄(CO)₁₁H]^?, an expected decompositioFn complex of the corresponding polynuclear formyl complex, [Ir₄(CO)₁₁CHO]^?.     

Fluorocarbon metal compounds—role models in organotransition metal chemistry

Early studies on organo-transition metal complexes with fluorocarbon ligands are reviewed in a historical context in relation to the renaissance of organometallic chemistry which followed the discovery of ferrocene.     

On the vibrational structure in inner-shell ionization spectra by a many-body approach

The vibrational structure due to the ionization of inner-shell electrons is calculated for methane and carbon monoxide. The vibrational coupling constants are renormalized by going up to second order perturbation theory. It is found that for core electrons the renormalization is essential. The results are compared with experimental spectra.     

Fragmentation and rearrangement processes in the mass spectra of perhalogenoaromatic compounds—VIII: Fluoroaromatic heterocyclic derivatives of group IV

The metastable ion supported fragmentations and fluorine transfer rearrangements of a series of fluoroaromatic heterocyclic derivatives of silicon, germanium and tin are reported. Of particular interest is the unique loss of neutral SiF₄ from the parent ion of (C₁₂F₈)Si yielding the [C₂₄F₁₂]⁺˙ ion. These and similar rearrangements are discussed and structures are proposed for some of the ions observed. The general case of cyclic rearrangement intermediates prior to the loss of neutral metal fluorides from perfluoroaromatic derivatives is discussed. Losses of neutral metal fluorides from the parent ions appear to involve a species with increased co-ordination number about the central atom as an intermediate. In addition to (C₁₂F₈)₂M, the following compound types were studied: (C₆H₅)₂Ge(C₁₂F₈), (C₁₂F₈S)₂M and R₄Sn₂(C₆F₄)₂ (where M = a Group IV metal and R = CH₃ or C₆H₅).     

Practical capillary gas chromatography—a systematic approach

Capillary gc is now rapidly expanding. Naturally, initiation is most often attempted on the basis of the experience acquired with packed columns. However, such an extrapolation is successful only if a number of essential peculiarities of capillary gc are considered. Based on practical examples this paper discusses six essential details: 1) design and maintenance of the gas flow paths, 2) the greatly increased importance of sampling technique, which should not be confined just to stream splitting, 3) the problems in quantitative analysis arising from small sample size, 4) specific sources of trouble related to small amounts of liquid phase, 5) specific arguments for the choice of the carrier gas, clearly pointing to hydrogen as the ideal carrier and, 6) the different way to approach column production. Figures for all selected examples are given.     

Energetics of hydrogen coverage on group VIII transition metal surfaces and a kinetic model for adsorption/desorption

We determined the binding energy of hydrogen to the closest packed surface for all nine group VIII transition metals as a function of surface coverage using quantum mechanics (density functional theory with the generalized gradient approximation) with periodic boundary conditions. The study provides a systematic comparison of the most stable surfaces of the nine group VIII transition metals, leading to results consistent with available surface science studies. We then use these to develop a simple thermodynamic model useful in estimating the surface coverage under typical heterogeneous catalysis conditions and compare these results to temperature programmed desorption experiments.     

Time-correlation function approach to many-body scattering in molecular systems

Energy transfer cross sections for collisions between atoms and molecular systems are related to time-correlation functions (TCFs) of the transition operators for scattering. The frequency Fourier transforms of the TCFs are studied within a Liouville-space formalism, and are shown to be lorentzian functions with frequency-dependent widths and shifts.     

Bridged ring systems—VIII A novel ring expansion reaction

Acid treatment of 2-(β-Benzoylethyl)-cyclopentanone (III) leads directly to a phenylcycloheptene carboxylic acid (VII) and the related lactone (XI), via a bicyclic intermediate.     

Organic semiconductors—metal phthalocyanine sheet polymers

This publication discusses the electronic, magnetic susceptibility, MS and GC–MS pyrolysis, X-ray powder diffraction, and electrical conductivity studies on metal phthalocyanine sheet polymers. The magnetic measurements over the range of magnetic field strengths 1025–6144 gauss indicated the absence of the intermolecular cooperative effect. MS and GC–MS studies indicate that all these metal phthalocyanine sheet polymers give benzene, cyanobenzene, and dicyanobenzene on thermal degradation. The electrical conductivity measurements showed that these polymers are semiconductor in nature.     

Contributions to the basic problems of complexometry—VIII Thioglycollic acid as a masking agent

The masking properties of thioglycollic acid (TGA) as well as the possibilities of its use in complexometry have been studied. It has been found that thioglycollic acid in an alkaline medium perfectly masks metals such as Pb, Bi, Cd, Ag, Hg, Zn, Tl, In and Sn because of the formation of colourless complexes. In this medium TGA forms intensely coloured complexes with Fe, Co and Ni. The red coloration of the Fe-TGA complex can be prevented by the addition of triethanolamine. It has been found that the Ni- and Co-EDTA complexes do not react with TGA. This enables a highly selective determination of nickel and cobalt to be made. Also, manganese can be determined in the presence of other metals screened with TGA. The advantages of TGA in comparison with potassium cyanide are discussed.     

Stereochemical studies—VIII Unequivocal determination of the absolute configuration in biaryl systems

According to the reaction sequences shown in Figs 1-5, the absolute configuration of optically active biaryl derivatives such as biphenyl, binaphthyl, bianthryl and bianthroaquinonyl have been clearly established, based on the standard compound (R)-(+)-I, in the binaphthyl system, whose absolute configuration was unequivocally determined by the anomalous X-ray diffraction method.