Browsing by Author "Thornton, David A"

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    Application of crystal field theory to the infrared spectra of transition metal complexes
    (1973) Shephard, Gordon Seymour; Thornton, David A
    [pages missing] problem in the IR spectra of 8-quinolinol chelqtes of di~ and trivalent metals of the first transition series. The metal-sensitivity of bands in the IR spectra of structura~ly differing substituted 8-quinolinol Qhelates ~eceives an interpretation in terms of crystal field theory. The effect of halogen and methyl substituents in the I~ spectra of the Cu(II) chelates is consistent with the band assignments based on crystal field effects P.nd is relat;.ep to both the resonance and inductive capacities of th~ substituents. A total of 232 compounds have been synthesized and are discussed.
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    Application of IR and NMR spectroscopy to certain complexes of 8-hydroxyquinoline and 8-aminoquinoline
    (1987) Knight, Cheryl Lynn; Thornton, David A
    The IR spectra of twenty-one transition metal complexes of 8-hydroxyquinoline over the range 700 - 50 cm⁻¹ are discussed in relation to their known or inferred structures. The complexes are of three types: (a) the bis(aquo) complexes of the first row transition metal(II) ions, [M(ox)₂(H₂O)₂] (M =Mn, Fe, Co, Ni, Cu, Zn); (b) the corresponding anhydrous complexes, [M(ox)₂]n (M=Mn, Co, Ni, Cu, Zn) and (c) the complexes of the metal(III) ions, [M(ox)₃] (M = Sc, V, Cr, Mn, Fe, Co, Ga, Rh and In). Deuterated 8-hydroxyquinoline was. synthesized by the Skraup synthesis and has been used to assist in the assignment of the metal-ligand modes. The assignment of these bands was further based on ⁶⁴,⁶⁸Zn labellihg of the bis(aquo) zinc chelate and on the effects of metal ion substitution in relation to structural considerations based on crystal field theory. An investigation of the IR spectra of a series of -tris, bis and mono(8-aminoquinoline) complexes of the first transition row metal(II) perchlorates and halides is reported.
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    Crystal field aspects of vibrational spectra
    (1969) Hancock, Robert Douglas; Thornton, David A
    Crystal Field Theory (C.F.T.), and its congeners, Ligand Field Theory (L.F.T.) and Molecular Orbital Theory (M.O.T.), have been most successful in explaining many of the properties of transition metal complexes. This is particularly true of their electronic spectra, magnetochemistry and chemical thermodynamic properties. However, these theories have been ignored in relation to the explanation of changes observed in the infrared spectra of series of transition metal complexes on change of central cation. The purpose of this work is to examine such changes in the light of these theories. The basis of the above theories is the splitting of the inner orbitals of the metal ions, due to the field of the ligands surrounding them. The field may be considered to arise from electrostatic repulsion by the ligand electrons (C.F.T.), or as a result of the chemical bonding between the central cation and the ligands (L.F.T. and M.O.T.). The result of this inner orbital splitting is stabilisation of the electrons of the orbital, as comparred with their energy in the absence of the field.
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    The effects of metal ion and ligand substitution on the spectroscopic properties of metal complexes.
    (1975) Johnson, Peter Robin; Thornton, David A
    Metal-nitrogen stretching vibrations in Co(II), Ni(II), Cu(II) and Zn(II) chloride 4-methylaniline complexes are assigned by ¹⁵N-labelling in conjunction with a consideration of the relative crystal field stabilizition energies of the metal ions. Bands in the ultraviolet electronic spectra of Cu(II) β-ketoenolate complexes are more conclusively assigned by comparison of the spectra of the β-ketoenolates, their sodium salts and the copper complexes. The effect of ligand substitution on the infrared spectra of Cu(II) benzoylacetanilide complexes and their methanol adducts is used to assign copper-oxygen stretching frequencies. The effect of ligand substitution on the ultraviolet electronic spectra is used to estimate the extent of π-interaction in these complexes. The infrared spectra of six ¹⁵N-labelled Co(II), Ni(II), Cu(II) and Zn(II) N-salicylideneanthranilate complexes yield assignments of metal-ligand and certain ligand vibrations. These assignments are supported by observing the effects of metal ion and ligand substitution on the spectra. The shifts observed in the metal-ligand stretching frequencies are related to the relative crystal field stabilization energies of the metal ions and to the electron releasing and withdrawing capacities of the ligand substituents. Assignments of metal-ligand vibrations in the infrared spectra of Ni(II) and Cu(II) benzoylbenzilidenehydrazone complexes and Co(II), Ni(II), Cu(II) and Zn(II) benzoylsalicylidenehydrazone complexes are made by observing the effects of metal ion and ligand substitution on the spectra. The infrared spectra of three ¹⁵N-labelled Ni(II), Co(II) and Cu(II) triarylformazan complexes yield assignments of metal-ligand and certain ligand vibrations. The effect of ligand substitution on the infrared spectra of Ni(II) triarylformazan complexes is related to the electron releasing or withdrawing capacities of the substituents. A total of 168 complexes, of which 131 have not previously been reported, has been synthesized and discussed.
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    Isotopic labelling : application to band assignments in the infrared spectra of metal complexes
    (1978) Rutherford, Phillip Edgar; Thornton, David A
    The technique of isotopic labelling is discussed in relation to its application to band assignments in the infrared spectra of metal complexes. ¹⁵N- and ²H-labelling are applied to three classes of transition metal coordination compounds.
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    Isotopic labelling applied to the infrared spectra of metal complexes
    (1980) Niven, Margaret Lilian; Percy, G C; Thornton, David A
    An ir investigation of a series of 2-aminomethylpyridine complexes of first transition metal(II) perchlorates, tetrafluoroborates, halides and thiocyanates is reported. Comparisons with the spectra of related complexes of 2,2'-bipyridine and ethylenediamine together with metal-ion substitution, deuteration and ¹⁵N isotopic labelling of the amino group in 2-aminomethylpyridine enable reliable band assignments to be made. The study shows that in complexes of the type M(amp)nX₂, metal-to-amino-nitrogen stretches occur at frequencies greater than 350 cm⁻¹ , while the metal-to-pyridine-nitrogen stretches are generally below 300 cm⁻¹, the assignment of the latter being generally complicated by the presence of metal-to-halogen vibrations. In addition to an x-ray crystallographic investigation of the complex [Ni(amp)₃](BF₃ ₄)₂, considerable structural information about these complexes is obtained from correlations between the number of M-L vibrations observed in the far ir and those predicted for localized molecular point symmetries on a group theoretical basis.
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    Isotopic labelling applied to the infrared spectra of metal complexes
    (1979) Hodgson, John Betton; Thornton, David A; Percy, G C
    An investigation of a series of imidazole complexes of first transition metal (II) nitrates, perchlorates and halides is reported. Deuteration of the imidazole ring provides reliable assignments for the internal vibrations of imidazole. This technique also permits unambiguous assignments of the internal vibrations of nitrate or perchlorate by their lack of deutero-sensitivity. The infrared spectra of imidazole and its complexes are examined in order to determine the ratio vD/ vH for bands as signed to the C-H, N-H and ring modes of the heterocyclic ring. With very few exceptions, vD/vH falls within the ranges 0. 74 to 0. 84 and 0. 93 to 1. 00 for C-H and ring vibrations, respectively. The potential usefulness of the results is discussed. Assignments of the M-N and M-halide vibrations are based on the results of the deuteration studies, metal ion substitution and on halogen substitution. The number of M-L vibrations in the far-infrared satisfies the selection rules for the molecular point or site group symmetries and facilitates accurate structural assignments.
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    Isotopic labelling applied to the infrared spectra of metal complexes
    (1977) Engelter, Carola; Thornton, David A
    The infrared spectra of pyridine adducts of first transition series metal(II) acetylacetonates are discussed in relation to the band shifts induced by ¹⁵N-labelling and deuteration of the pyridine ring and by metal ion substitution. ¹⁵N-Labelling aids in establishing the pyridine ring vibrations, while deuteration and metal substitution are more useful in assigning the νM-L frequencies. Results of the isotopic labelling study lead to a revision of previously-reported νM-O and vC---O frequencies. This technique also facilitates assignment of the νM-N vibrations, observed in the region below 200 cm⁻¹. The occurrence of these bands in this spectral region was expected because of the known relative weakness of the M-N bond strength in pyridine adducts. The effects on the spectra resulting from introduction of a variety of substituents into the pyridine ring are discussed on the basis of the electronic effects of the substituents. After allowing for mass effects, electron-withdrawing substituents are found to decrease νNi-N frequencies while electron-releasing substituents exert negligible effect on the νNi-N bands. An opposite trend is, however, observed for the νNi-O bands and is explained. An investigation of a series of aniline and p-toluidine complexes of first transition metal(II) isothiocyanates is reported.
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    Ligand isotope vibrational studies of metal(II) complexes with particular reference to heterocyclic N-oxides
    (1987) Watkins, Gareth Mostyn; Thornton, David A
    A critical examination of the characteristic N-O vibrational frequencies of aromatic N-oxides questions the widely held assignment of αN-O (840cm⁻¹) and YN-O (47oon- 1). The present investigation supports the assignments of αN-O (470cm⁻¹) and γN-O (280cm⁻¹), with the assignment of the band at 840cm⁻¹ as being vring coupled with νN-O.
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    Metal ion cages with stabilized conformations : synthesis, characterization and properties
    (1989) Naidoo, Kevin Jonathan; Hendry, Tony; Thornton, David A
    The stabilized conformers lel₃, lel₂ob, ob₂lel and ob₃ of the [Co(±pn)₃]³⁺ system have previously been synthesized giving relative equilibrium (100 °C) amounts of 35.0 : 41.1 : 18.0 : 4.0. With the recent encapsulation of the resolved lel₃-[Co(pn)₃₋]Cl₃ complexes, and their subsequent interconversion to the ob₃-[Co(NH₃)₂-pnsar]Cl₅ diastereomers, the synthesis of the lel₂ob and ob₂lel cage complexes is a necessity to complete the investigation of the [Co(NH₃)₂-pnsar]⁵⁺ system. Consequently the eight Δ, Λ isomers of the lel₂ob-[Co(NH₃)₂-pnsar]Cl₅ complex were synthesised in a one pot reaction and resolved into the respective isomers having the following relative yields: lel₂ob-1 (~ 24% ), lel₂ob-2 ( ~ 43% ), lel₂ob-3 ( ~ 28%) and lel₂ob-4 (~ 5%). The resolution order of these isomers on SP Sephadex C-25 was used to tentatively identify the (3 mer and 1 fac) geometrical isomers of these lel₂ob diastereomers. For the first time ob character was directly encapsulated with the synthesis of the ob₂lel-[Co(NH₃)₂-pnsar]Cl₅ conformers ( ~ 1 % ). NMR analysis showed these to consist almost entirely (80%) of the ob₂lel-1 isomer. The geometry of this isomer was later discovered to be most favourable when the lel₂ob-1 isomer gave a 50% conversion to the ob₂lel-1 isomer, unlike the poor conversions of the ob₂lel-2 (~ 5%) and the ob₂lel-3 (~ 15%). The electronic spectra (UV /VIS and CD) of the individual isomers were investigated and revealed the presence of large distortion of the CoN₆ chromophore from regular Oh geometry. This was confirmed by the crystal structural analysis of the lel₂ob-2 isomer which reveal a trigonal twist angle (ф) of ~ 45°. The crystal structure also proved the identification logic right, which was based on the relation between chemical and resolution order evidence. The infrared spectra of [Co(NH₃)₂-sar]⁵⁺ ion was analysed using isotopic labelling methods in combination with the results of group theory calculations. These assignments make it possible to study the spectra of the [Co(NH₃)₂-pnsar]⁵⁺ isomeric complexes. Comparison of the infrared spectra of these complexes reflect the increase in number of bands on progressing from D₃, through C₃ to C₁ symmetry. Even the orientation of methyl groups in the different conformer types affect the symmetry of the CoN₆ core.
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    Spectroscopic studies of Metal(II) complexes and application of the Ni(II) complexes to olefin oligomerisation catalysis
    (1990) Bennett, Alison Margaret Anne; Thornton, David A; Foulds, Gary André
    Complexes of some divalent first row transition metal ions with various ligands have been prepared. These included bis-complexes of β-ketoenolate ligands, nickel complexes of trialkylphosphine and nickel complexes containing phosphine and β-ketoenolate ligands, and finally, tris, bis and mono(ethylenediamine) complexes. Composition was ascertained by microanalysis and ¹H, ¹³C NMR of the diamagnetic complexes. In addition, the crystal structure of one of the nickel β-ketoenolate triethylphosphine complexes was determined. The infrared spectra of the above compounds have been examined over the range 4000-50 cm⁻¹ with a view to determining band assignments based on metal ion substitution, ligand substitution (for phosphine and β-ketoenolate complexes), ligand and metal ion isotopic labelling [for tris(ethylenediamine) complexes] and anion substitution (for phosphine and ethylenediamine complexes). In each case, spectra-structure correlations have been established and are discussed. Each of the nickel complexes prepared above was tested as a catalyst for the oligomerisation of 1-hexene. The experiments were carried out in batch at 40°C using toluene as solvent. Four different Lewis acid cocatalysts were tested and nickel : co-catalyst ratios of 1:1 and 1:10 were used. The effects of Lewis acid strength and concentration, nickel complex structure, a change in the donor chelating atom and the presence of phosphine ligands on the isomerisation, as well as the activity and selectivity of the oligomerisation reaction, are discussed. Two polymer-supported catalyst complexes have been prepared; the first,: by polymerisation of a nickel β-ketoenolate complex monomer and th, second, by binding a nickel β-ketoenolate phosphine complex to a polystyrene support through the phosphine ligand. The resultinJ polymers were extensively characterised by microanalysis, infrared, ¹H and ¹³C NMR, mass spectrometry, energy dispersive X-ray and thermal techniques. In the presence of a ten-fold excess of the ethylaluminium dichloride co-catalyst, each supported complex formed an active 1-hexene oligomerisation and isomerisation system. The activity and selectivity of each system have been compared to that of their respective monomers. Finally, the polymerised ,8-ketoenolate monomer was tested at various temperatures as a propene oligomerisation catalyst and the effect of temperature on activity and selectivity is discussed.
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    A spectroscopic study of square planar platinum (2) complexes
    (1983) Hall, Philip Simon; Thornton, David A; Foulds, Gary André
    A number of spectroscopic techniques consisting of ultraviolet, ¹H-NMR and mass spectrometry have been used in the structural analysis of square planar Pt(II) complexes. The complexes trans-[PtBr₂(Y) (R-an)] (Y = C₂H₄,CO; R-an = substituted aniline) were prepared and investigated by the spectrosopic techniques. Infrared assignments were aided by isotopic labelling studies. The discussion of the two series of complexes are based on their relation to one another. The complexes trans-[PtX₂ (CO) (L)] (X = Cl, Br; L = aniline, pyridine N-oxide, pyridine, ammonia, imidazole and pyrazole) were prepared from their corresponding ethylene analogues. Infrared assignments, with labelling studies, are given for the complexes. The bonding effects in these complexes were studied using ¹H-NMR and ultraviolet spectroscopy. The ¹H-NMR spectra reveal that there is a fluxional behaviour of the ligands in some of the complexes. Hence, cold temperature studies were required to "freeze out" this fluxional behaviour and observe the expected signals due to the ¹⁹⁵pt-H coupling. The electronic effects are different when the ligand, L, was capable of forming σ-bonds with Pt²+, compared to when L was capable of forming both a- and π-bonds with Pt²+. The mass spectra show the M+ peak and subsequent fragmentation in the complexes. The fluxional behaviour of imidazole in trans-[PtX₂(C₂H₄) (Him)] was monitored by cold temperature studies. Using band shape analysis (with the aid of a computer) the activation paramaters for the exchange processes were determined. The dependence of the imidazole proton signals on temperature, solvent and excess ligand, all indicate that an intermolecular exchange process is occurring. Studies on the complex trans-[PtX₂(C₂H₄) (pyz)] and the effect of solvent on the complexes are being pursued, and it is hoped that an understanding of the role of the solvent in the exchange process will become apparent.
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    A spectroscopic study of square planar platinum (II) complexes
    (1982) Foulds, Gary André; Thornton, David A
    A number of spectroscopic techniques consisting of infrared, Raman ultraviolet and 1H-nmr spectroscopy have been used in the structural analysis of square planar Pt(II) complexes.
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    A spectroscopic study of square planar rhodium(I) complexes
    (1989) Hall, Philip Simon; Jackson, Graham Ellis; Moss, John R; Thornton, David A
    Ninety square planar Rh(I) complexes of the type cis-[Rh(CO)₂(X)(L)], [Rh(COD)(X)(L)], [Rh(CO)₂(L)₂]ClO₄ and [Rh(COD)(L)₂]ClO₄ (X is Cl or Br; COD is 1,5-cyclooctadiene; L is aniline, pyridine, pyridine N-oxide, imidazole and ammonia), as well as their isotopically labelled derivatives (¹³CO, ²H and ¹⁵N) were prepared, characterized by microanalysis and melting point, and investigated by the following spectroscopic techniques: infrared, Raman, ultraviolet, mass spectrometry, and 1H, ¹³C and ¹⁵N nmr spectroscopy. The comprehensive isotopic labelling studies allowed unambiguous assignment of the infrared modes in the 4000-50 cm⁻¹ region. The infrared assignments are discussed with reference to their vᴰ/Vᴴ ratios, the various ligands and halogens used, the charges on the complexes, and are compared to similar compounds. The 1H, ¹³C and ¹⁵N nmr runs were performed at room and low temperatures. Fluxionality of the ligands (L) was observed and the exchange process was monitored by variable temperature nmr. The enthalpy and entropy values for the intermolecular exchange of L in the complexes cis-[Rh(CO)₂(X)(L)] were obtained by a complete computer simulated band shape analysis of the carbonyl region of the ¹³C nmr spectra. The non-equivalence, and specific assignment of the carbonyl groups in the cis- [ Rh(CO)₂(X)(L)] complexes were determined by recording the variable temperature ¹³C nmr spectra of the doubly enriched species cis[Rh(¹³CO)₂(X)(¹⁵N-ligand)]. ²J(¹³C-Rh-¹⁵N) values are reported for the first time. The ¹J(¹⁵N-¹⁰³Rh) coupling constants are rationalized in terms of the metal-nitrogen bonding, and correlate with the s-character of the bonding electron on nitrogen. While the solution electronic spectra reveal that the complexes are discrete monomeric entities in solution, there are indications of metal-metal interactions in the solid-state. The normal coordinate analysis study of the complexes cis-[Rh(CO)₂(X)(L)] involved the calculation of a general valence force field by applying the eigenvector method of Becher and Mattes. The results show that point-mass-modelling and simplified force field, as assumed in our treatment, describes, to a good approximation, the vibrational properties of the complexes. The potential energy distribution provided further support for the proposed infrared assignments of the complexes.
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    Studies in the field of metal β-ketoenolate chemistry
    (1970) Haigh, John Michael; Thornton, David A
    The syntheses of 188 metal complexes and 19 ligands (the majority of which are newly reported here) are described. These were individually studied by several physical techniques including IR spectroscopy, NMR spectrometry, conductance determinations and magnetic susceptibility determinations. The NMR spectra of 42 variously substituted pyridines were determined. The results are used to discuss the nature of the bonding and structure of these molecules.
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    Synthetic, structural and electrochemical studies of some transition metal carbonyl and nitrosyl complexes
    (1977) English, Robert Bertram; Haines, R J; Nassimbeni, Luigi R; Thornton, David A
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    Thick target pixe analysis
    (1993) Pineda-Vargas, Carlos A; Peisach, Max; Thornton, David A
    The evaluation of the physical parameters governing the X-ray yield production in thick targets by charged particles was investigated and matrix correction factors (MCF) were calculated for a wide variety of materials including values for all pure non-gaseous elements or their compounds for the Kα and Lα X-ray lines. These factors were calculated for 1, 2, 3 and 4 MeV proton bombarding energies. A new methodology named 'common matrix type' (CMT) was developed for the determination of trace element concentrations in carbon-rich materials, such as most biological materials, with unknown matrix composition. A universal set of matrix correction factors (MCF) values for these materials was established for trace elements with Z ≥ 19 and irradiations with proton energies in the range of 1 to 4 MeV. A similar methodology was developed for silicon-rich and calcium-rich materials where the main components, Al, Si and Ca do not vary appreciably in their concentrations. CMT methodologies were applied successfully for the determination of trace elemental concentrations in a wide variety of thick target materials, which included archaeological cultural materials, biological tissues and geological ores. The technique of correspondence analysis was used for the statistical analysis of the extended data matrix generated in most of the applications. This technique of interpretation of multielemental data proved to be a valuable tool. Two modes of PIXE application, macro-mode and micro-mode, were evaluated at different ion bombarding energies ranging from 1 to 85 MeV. Experimental X-ray production cross sections at 66 and 85 MeV were evaluated and found to correlate well with theory based on the plane wave Born approximation (PWBA) for the Kα and Kβ lines. It was found that the irradiation of intermediate thickness samples of geological ores by energetic protons (66 MeV) is a suitable technique for the determination of small traces of rare earth metals with detection limits for analysis expected to be below the μg.g-1 range. The fact that energetic protons can be used means that no need for matrix correction is necessary. Micro-PIXE with low energy protons was found suitable for the determination of small traces of metals in human kidney stones and for the study of interrelationships between trace element concentrations with time of stone formation, in stones excreted from a single patient.