This thesis is principally concerned with the interaction of cobalt porphyrin complexes with halocarbons. There have been no previous studies of these, despite the afct that the ability to readily introduce substituents into the porphyrin ligand makes it ideal for inducing subtle electronic and steric changes into the complexes. The reactions of various substituted cobalt tetraphenylporphyrins with halocazbons was studied. Three series of experiments were performed involving activation by heat, visible light and ultraviolet light. Products were characterized by electronic, nmr and mass spectrometry. The five coordinate complexes, [CoX (Por)] , obtained from thermally activated reactions and those performed with uv irradiation under nitrogen, proved particularly difficult to characterize since they are subject to disproportionation giving paramagnetic products. This aspect is discussed in detail and the results obtained allow clarification of conflicting reports in the literature. A qualitative investigation of relative reaction rates has led to the tentative suggestion that thermal reactions proceed by an electron transfer mechanism, whereas an atom abstraction mechanism applies to reactions involving activation by ultraviolet light. No reaction took place between cobalt porphyrins and the substrates in the presence of visible light. Aerobic ultraviolet radiation results in the formation of cobalt porphyrin [pi]-cation radicals with either a1u or azU. ground states, depending on the substituent pattern of the porphyrin. The cobalt porphyrins were all shown to possess catalytic activity for halocarbon-alkene addition reactions. Furthermore, studies in this area suggest that the catalytic activity could be correlated wíth the substituent pattern on the porphyrin ligand and, thus, complements the studies described above. A related rhodium complex was also synthesized and examined but was shown to have a disappointingly low catalytic activity. Products of [RuC1[sub]2z(PPh[sub]3)[sub]3] -catalysed additions of halocarbons to cyclohexa-1,3-diene were investigated by chromatographic and spectroscopic analyses to ascertain the stereochemistry of the products. The ratio of the two isomeric products was found to depend on steric effects of the addend groups, CX[sub]3 (X = Cl, Br) and X (X = Cl, Br).

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Cheng, Kai Hong. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references (leaves 134-141). / Abstracts in English and Chinese. / Abstract --- p.i / Acknowledgement --- p.iv / Table of Contents --- p.v / List of Figures --- p.viii / List of Tables --- p.xix / Chapter iii. --- Table of Contents / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Semiconductor spintronics --- p.1 / Chapter 1.1.1 --- Overview --- p.1 / Chapter 1.2 --- Dilute magnetic semiconductors (DMS) --- p.2 / Chapter 1.2.1 --- Historical background --- p.3 / Chapter 1.2.2 --- Their importance and significance --- p.4 / Chapter 1.2.3 --- Material systems showing room temperature ferromagnetism --- p.5 / Chapter 1.3 --- Cobalt (iron)-doped titanium dioxide as DMS --- p.7 / Chapter 1.3.1 --- Structures and properties of titanium dioxide --- p.8 / Chapter 1.3.2 --- Various preparation techniques of cobalt (iron)-doped titanium dioxide --- p.10 / Chapter 1.3.3 --- This thesis --- p.13 / Chapter Chapter 2 --- Sample Preparation and Characterization Techniques --- p.14 / Chapter 2.1 --- Sample preparation --- p.14 / Chapter 2.1.1 --- RF magnetron sputtering --- p.14 / Chapter 2.1.2 --- MEVVA ion implantation --- p.17 / Chapter 2.1.3 --- Sample preparation conditions --- p.19 / Chapter 2.2 --- Characterization techniques --- p.24 / Chapter 2.2.1 --- Structural characterization --- p.24 / Chapter 2.2.1.1 --- Rutherford backscattering spectrometry (RBS) --- p.24 / Chapter 2.2.1.2 --- X-ray diffraction (XRD) --- p.26 / Chapter 2.2.1.3 --- X-ray photoelectron spectroscopy (XPS) --- p.28 / Chapter 2.2.1.4 --- Transmission electron microscopy (TEM) --- p.31 / Chapter 2.2.2 --- Vibrating sample magnetometry (VSM) --- p.33 / Chapter 2.2.3 --- Temperature varying resistivity measurements --- p.35 / Chapter Chapter 3 --- Characterization of Titanium Dioxide Samples --- p.40 / Chapter 3.1 --- RBS results --- p.40 / Chapter 3.2 --- XRD results --- p.43 / Chapter 3.3 --- XPS results --- p.47 / Chapter 3.4 --- Summary --- p.51 / Chapter Chapter 4 --- Characterization of Cobalt-implanted Titanium Dioxide Sample --- p.53 / Chapter 4.1 --- Cobalt dose dependence --- p.53 / Chapter 4.1.1 --- RBS results --- p.53 / Chapter 4.1.2 --- XRD results --- p.65 / Chapter 4.1.3 --- VSM results --- p.69 / Chapter 4.1.4 --- Temperature varying resistivity measurements --- p.75 / Chapter 4.2 --- Effects of annealing temperature --- p.77 / Chapter 4.2.1 --- RBS results --- p.77 / Chapter 4.2.2 --- XRD results --- p.79 / Chapter 4.2.3 --- XPS results --- p.83 / Chapter 4.2.4 --- TEM results --- p.88 / Chapter 4.2.5 --- VSM results --- p.91 / Chapter 4.2.6 --- Temperature varying resistivity measurements --- p.97 / Chapter 4.3 --- Summary --- p.99 / Chapter Chapter 5 --- Characterization of Iron-implanted Titanium Dioxide Samples --- p.101 / Chapter 5.1 --- Iron dose dependence --- p.101 / Chapter 5.1.1 --- RBS results --- p.101 / Chapter 5.1.2 --- XRD results --- p.107 / Chapter 5.1.3 --- VSM results --- p.110 / Chapter 5.1.4 --- Temperature varying resistivity measurements --- p.114 / Chapter 5.2 --- Effects of annealing temperature --- p.116 / Chapter 5.2.1 --- RBS results --- p.116 / Chapter 5.2.2 --- XRD results --- p.117 / Chapter 5.2.3 --- VSM results --- p.119 / Chapter 5.2.4 --- Temperature varying resistivity measurements --- p.121 / Chapter 5.3 --- Summary --- p.122 / Chapter Chapter 6 --- Conclusion and future work --- p.125 / Appendices --- p.127 / Bibliography --- p.134 / Publications --- p.141 / Chapter iv. --- List of Figures / Fig. 1.1 Crystal structures for two most stable polymorphs of TiO2: (a) anatase; and (b) rutile --- p.9 / Fig. 2.1 Schematic of RF sputtering system --- p.15 / Fig. 2.2 Motion of electrons emitted for the target surface (a) in the applied magnetic field (-z direction); (b) in the applied electric field (-y direction) and magnetic field (-z direction) --- p.16 / Fig. 2.3 Schematic of the implanter with the MEVVA ion source --- p.17 / Fig. 2.4 The TRIM ion distribution profile of Co atoms in anatase TiO2 by implantation to a Co dose of 2.2 x 1016 cm-2 at an extraction voltage of 65 kV --- p.21

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. December 2015. / It is well-established that there is electronic communication between the equatorial and axial ligands in the cobalt corrins. It can therefore be anticipated that the electronic structure of the corrin ligand will affect the chemistry of the axial coordination sites of Co(III) in these complexes. To probe this cis-influence the electronic structure of the corrin was perturbed by substituting the H atom at C10 by Br (which is π electron-donating towards the corrin) in aquacobalamin ([H2OCbl]+), and by NO2 (which is strongly electron-withdrawing) and NH2 (which is strongly electron-donating) in aquacyanocobester ([ACCbs]+). The first part of this study was dedicated to aqua-10-bromocobalamin ([H2O-(10-Br)Cbl]+) and the second part to aquacyano-10-nitrocobester ([AC-(10-NO2)Cbs]+) and aquacyano-10-aminocobester ([AC-(10-NH2)Cbs]+). The successful synthesis of [H2O-(10-Br)Cbl]+, was verified by ESI-MS, 1H and 13C NMR, uv-vis spectroscopy and XRD. The stability constants for the substitution of coordinated H2O by a series of anionic (N3 –, NO2 –, SCN–, SO3 2–) and neutral N-donor ligands (imidazole, DMAP) were obtained for [H2OCbl]+, [H2O-(10-Br)Cbl]+ and [H2O-(10-Cl)Cbl]+ under the same conditions. Substitution of the C10 H by Cl or Br favours the coordination of anionic ligands, but discriminates against the binding of neutral N-donor ligands. The anionic ligands bind more strongly to [H2O-(10-Br)Cbl]+ than to [H2OCbl]+ with log K values between 0.05 and 0.62 (average 0.33) larger. Conversely, neutral ligands bind less strongly to [H2O-(10-Br)Cbl]+ than to [H2OCbl]+ with log K values between 0.29 and 0.36 (average 0.33) smaller. DFT (BP83/TZVP) calculations were used to rationalise these observations. When H is changed to Cl or Br, the metal ion becomes less positive. When the β ligand changes from a neutral to an anionic ligand, the partial charge on the C10 substituent becomes more negative. Replacing C10 H by Cl or Br discriminates against a neutral ligand because of the greater electron richness of the metal. If the ligand is an anion, however, the charge donation can be accepted by delocalisation onto the C10 substituent. The reaction kinetics of the substitution of H2O in [H2O-(10-Br)Cbl]+ were determined for the ligands N3 – and imidazole and were compared with values available for [H2OCbl]+ and [H2O-(10- Cl)Cbl]+. The results showed that both N3 – and imidazole react more slowly with [H2O-(10- Br)Cbl]+ than with [H2OCbl]+, consonant with the previous observations for [H2O-(10-Cl)Cbl]+. Although ΔH‡ values are smaller, they do not compensate for significantly more negative values of ΔS‡, indicative of a transition state that occurs earlier along the reaction coordinate in [H2O- (10-Br)Cbl]+ and [H2O-(10-Cl)Cbl]+ whereas the transition state occurs later along the reaction coordinate with [H2OCbl]+. It is argued that this is a consequence of the lower charge density on the metal, making it a better electrophile both towards the incoming and the departing ligand. Dicyano-10-nitrocobester ([DC-(10-NO2)Cbs]) and dicyano-10-aminocobester ([DC-(10- NH2)Cbs]) were synthesised from dicyanocobester [DCCbs] by established methods and converted to the aquacyano form so that the thermodynamics and kinetics of the substitution of coordinated H2O by a variety of ligands could be investigated. The stability constants for the substitution of coordinated H2O by a number of neutral (imidazole, DMAP, methylamine) and anionic (N3 –, NO2 –, SCN–, SO3 2–, CN–) ligands were determined for [ACCbs]+, [AC-(10-NO2)Cbs]+ and [AC-(10-NH2)Cbs]+ in 50% isopropanol. The soft anions (SO3 2– and CN–) bind better to the softer Co(III) metal centre in [AC-(10-NH2)Cbs]+ and [ACCbs]+ than in [AC-(10-NO2)Cbs]+ and the converse is true for the hard anions (N3 –, NO2 – and SCN–). The case is less clear for the N-donor ligands; DMAP clearly has a higher affinity for [AC-(10- NH2)Cbs]+ and [ACCbs]+ than for [AC-(10-NO2)Cbs]+, but there is little discrimination in the case of imidazole and methylamine. This implies that the affinity of the metal for an exogenous ligand depends on the electron density at the metal centre. DFT calculations showed that as the C10 substituent is changed from NH2 to H to NO2, the charge density on the metal centre decreases and the metal becomes harder. The kinetics of the substitution of H2O by CN– in [ACCbs]+, [AC-(10-NO2)Cbs]+ and[AC-(10- NH2)Cbs]+ in 50% isopropanol were determined. The results showed that the substitution of coordinated H2O proceeded with biphasic kinetics and through a dissociative interchange (Id) mechanism where there is nucleophilic participation of the entering ligand in the transition state. The slower phase corresponds to the substitution of coordinated H2O trans to OH– in the aqua hydroxo species, which, together with the dicyano species, is inevitably present in solutions of [ACCbs]+, and the faster phase corresponds to the substitution of the coordinated H2O trans to CN– in the aquacyano species. The difference in rate of the reaction of the [AC-(10-Z)Cbs] (Z = H, NH2 and NO2) was not very large, the ratio between the largest (for Z = H) and the smallest (for Z = NO2) is just over 40, and does not follow the electron donor properties of Z. This is misleading, however, because of a compensation effect between ΔH‡ and ΔS‡. As values of ΔH‡ become smaller, which causes an increase in the reaction rate, ΔS‡ becomes less positive (or more negative), which causes a decrease in the reaction rate. Hence, comparing rate constants at any particular temperature is not very informative and the compensation effect masks the very significant differences in the reactivity of the metal ion towards the entering CN– ligand. The compensation effect is attributed to the position of the transition state along the reaction coordinate, which depends on the charge density on the metal ion. Indeed, if all three reactions had the same value of ΔS‡ then the values of the rate constant would be in the approximate ratio 109:106:1 for Z = NH2, H and NO2, respectively. This study shows that how profoundly the perturbation of the electronic structure of the corrin affects the thermodynamic and kinetic properties of the Co(III) ion, and provides further evidence that the unusual chemistry of Co(III) in the cobalt corrins is a consequence of the cis-influence of the equatorial macrocyclic ligand. / LG2017

Thesis (Ph.D. (Physics)) --University of Limpopo, 2013 / The intention of the current study is to investigate structure, ion transport and reactivity of various forms of the cobalt pentlandite, Co9S8, at different temperatures using atomistic simulation methods with the support of electronic structure calculations. The first interatomic potentials of Co9S8 were derived with input data as structure and elastic properties from experiment and electronic structure calculations respectively. The potentials were validated by running energy minimization and molecular dynamics calculations. Structure, elastic properties and phonon spectra were well reproduced, together with the complex high temperature transformations and melting of Co9S8 as deduced from crystal structure, radial distribution functions, density profiles and diffusion coefficients. Amongst the high symmetry surfaces {111}, {101} and {101} atomistic surface energy calculations proposed the {111} surface of Co9S8 as the most stable in agreement with experimental morphologies, and water adsorption energies on the such surfaces which mostly agreed with those from electronic structure calculations. The structural and ion transport variations with temperature were investigated and predicted surface melting at lower temperatures than the bulk. The effects of hydration on the surfaces at low and high temperatures were also studied. The structural and ion transport properties of Co9S8 nanoparticles of varying sizes, covered by high symmetry surfaces {111}, {101} and {100} were predicted using molecular dynamics method based on our derived interatomic potentials. The structural and ion transport properties of Co9S8 nanoparticles of varying sizes, covered by high symmetry surfaces {111}, {101} and {100} were predicted using molecular dynamics method based on our derived interatomic potentials. Generally for {111}, {101} nanoparticles, high temperature transitions were abrupt for smaller nanoparticles and these tended to disintegrate and form voids. However, for larger nanoparticles the transitions were more gradual. Transitions in the {100} bound nanoparticles were less dramatic for all sizes and the formation of voids was reduced at high temperatures. Generally, the melting temperatures of different sizes of nanoparticles increases with the particle size hence approach the bulk limit. The interaction of nanoparticles with water was investigated. / Anglo Platinum, National Research Foundation (South Africa), and The Royal Society (UK)

Includes Publications resultant of the thesis research Includes bibliographical references (leaves 180-196). Electronic publication; full text available in PDF format; abstract in HTML format. A series of new cobalt(II) ℓ-keto iminato complexes and cobalt(II) salens have been made and the effect of chirality in the northern, southern and peripheral quadrants of these catalysts, with respect to induced enantiomeric excess, during ring-opening of 1,2-dioxines has been determined. Electronic reproduction.[Australia] :Australian Digital Theses Program,2001. ix, 206 leaves : ill. ; 30 cm.

The new Co(III) carbonate complexes [Co(uns-penp)(O₂CO)]ClO₄�H₂O and [Co(trpyn)(O₂CO)]ClO₄, containing tripodal tetraamine ligands, have been synthesised and characterised by microanalysis, �H, ��C and ⁵⁹Co NMR, mass spectrometry (MS) and UV-vis spectroscopy. In addition, the ⁵⁹Co NMR spectra have been obtained for two series of [Co(N₄)(O₂CO)]⁺ complexes containing aliphatic (N₄ = tren, baep, abap, trpn) and pyridyl (N₄ = tpa, pmea, pmap, tepa) tripodal tetraamine ligands and the complex [Co(dppa)(O₂CO)]⁺. The ⁵⁹Co NMR signal increases as [Delta] decreases, indicating there is less electron density at the Co(III) nucleus as the metal-ligand orbital overlap becomes poorer. A linear relationship was found to exist between the [Delta] for the individual complexes and their ⁵⁹Co NMR chemical shifts which follows the relationship: [Delta] = 29 174 + -0.89363 x [delta](⁵⁹Co) For the two series of [Co(N₄)(O₂CO)]+ complexes, plots of the magnetogyric ratio (γ) and [lambda][max] have y-intercepts that do not accurately correspond to the magnetogyric ratio of the bare cobalt nucleus (γ₀(Co)). This is due to the deviation of the complexes from pure octahedral symmetry. A fluxional process in the complex [Co(pmea)(O₂CO)]⁺ was investigated using variable temperate (VT) NMR. This was found to involve the inversion of a six-membered chelate ring about a pseudo mirror plane with a [Delta]G[double dagger] of 58 kJ mol⁻� at 25 �C. Mass spectra have been obtained for all the [Co(N₄)(O₂CO)]⁺ complexes, and these show a common fragmentation pattern for all the complexes except [Co(trpn)(O₂CO)]⁺, where CO₂ is lost from the molecular ion to give a [Co(N₄)O]⁺ adduct. Single crystal X-ray structural analyses were performed on [Co(abap)(O₂CO)]ClO₄ (orthorhombic, Pca2₁, a = 15.9744(11) Å, b = 8.6200(6) Å, c = 21.8568(15) Å, α = β = γ = 90�, Z = 8, R1 = 0.0350, wR2 = 0.0902), [Co(trpn)(O₂CO)]ClO₄�H₂O (monoclinic, P2₁/c, a = 11.9510(19) Å, b = 12.0740(19) Å, c = 12.917(2) Å, β = 117.56(4)�, α = γ = 90�, Z = 4, R1 = 0.0476, wR2 = 0.1188), [Co(tpa)(O₂CO)]ClO₄�2H₂O (triclinic, P-1, a = 16.2298(5) Å, b = 17.2291(5) Å, c = 17.3393(5) Å, α = 106.760(1)�, β = 92.809(1)�, γ = 108.004(1)�, Z = 8, R1 = 0.0349, wR2 = 0.0799), [Co(uns-penp)(O₂CO)]ClO₄�H₂O (triclinic, P-1, a = 6.7544(3) Å, b = 11.5523(5) Å, c = 12.3201(6) Å, α = 73.397(2)�, β = 89.749(2)�, γ = 84.551(2), Z = 2, R1 = 0.0277, wR2 = 0.0842) and [Co(trpyn)(O₂CO)]ClO₄ (monoclinic, P2₁/n, a = 12.2777(5) Å, b = 11.9322(4) Å, c = 27.9622(11) Å, β = 100.082(2)�, α = γ = 90�, Z = 8, R1 = 0.0435, wR2 = 0.1130). Rates of acid hydrolysis of [Co(N₄)(O₂CO)]⁺ (N₄ = baep, abap, trpn, tpa, pmea, pmap, tepa, uns-penp, dppa, trpyn, Me₃-tpa) complexes were measured by stopped flow or UV-vis spectroscopy (I = 1.0 mol L⁻�). The product of acid hydrolysis of [Co(pmea)(O₂CO)]⁺ has been indentified by X-ray crystallography as [Co(pmea)(OH₂)₂]�⁺ (triclinic, P-1, a = 9.7065(5) Å, b = 15.5645(8) Å, c = 11.5740(5) Å, α = 84.660(1)�, β = 123.255(1)�, γ = 104.283(1)�, Z = 2, R1 = 0.0402, wR2 = 0.1009). The acid hydrolysis reactions of the [Co(N₄)(O₂CO)]⁺ complexes containing aliphatic (N₄ = baep, abap, trpn) tripodal tetraamine ligands and [Co(tpa)(O₂CO)]⁺ and [Co(Me₃-tpa)(O₂CO)]⁺ have been investigated over the range [H₃O⁺] = 0.10 - 1.0 mol L⁻� Three processes were observed for the hydrolysis of [Co(baep)(O₂CO)]⁺, [Co(abap)(O₂CO)]⁺ and [Co(trpn)(O₂CO)]⁺ at all [H₃O⁺]. The first and second processes were thought to be [H₃O⁺] dependent, while the third was fit to a first order exponential decay and was [H₃O⁺] independent (k[obs] ~ 4.2 x 10⁻� s⁻� for [Co(baep)(O₂CO)]⁺, 3.8 x 10⁻� s⁻� for [Co(abap)(O₂CO)]⁺ and 3.5 x 10⁻� s⁻� for [Co(trpn)(O₂CO)]⁺). However, none of the processes could be confidently assigned to a step in the acid hydrolysis mechanism. The data obtained from the studies of [Co(tpa)(O₂CO)]⁺ and [Co(Me₃-tpa)(O₂CO)]⁺ showed a single first order [H₃O⁺] dependent process which was fit to the following expression: k[obs] = (k₁K[H₃O]⁺)/(1 + K[H₃O]⁺ This gave k₁ = 5.8 x 10⁻⁴ � 2.3 x 10⁻⁴ s⁻� and K = 0.13 � 0.06 L mol⁻� for [Co(tpa)(O₂CO)]⁺ at 25 �C and k₁ = 6.0 x 10⁻⁵ � 2.0 x 10⁻⁶ s⁻� and K = 0.38 � 0.02 L mol⁻� for [Co(Me₃-tpa)(O₂CO)]⁺ at 50 �C. Both values of K indicate that protonation of chelated carbonate is far from complete at [H₃O⁺] = 1.0 mol L⁻�. Comparative rates of acid hydrolysis at [H₃O⁺] = 6.0 mol L⁻� were obtained for the complexes [Co(tpa)(O₂CO)]⁺ (k[obs] = 1.79 x 10⁻� s⁻�, 25 �C), [Co(pmea)(O₂CO)]⁺ (k[obs] = 1.8 x 10⁻⁵ s⁻�, 25 �C), [Co(pmap)(O₂CO)]⁺ (k[obs] = 2.5 x 10⁻⁵ s⁻�, 50 �C), [Co(tepa)(O₂CO)]⁺ (k[obs] = 4.3 x 10⁻⁵ s⁻�, 25 �C) and [Co(trpyn)(O₂CO)]⁺ (k[obs] = 1.3 x 10⁻⁴ s⁻�, 50 �C) and at [H₃O⁺] = 1.0 mol L⁻� for the complexes [Co(uns-penp)(O₂CO)]⁺ (k[obs] = 2.9 x 10⁻� s⁻�, 25 �C) and [Co(dppa)(O₂CO)]⁺ (k[obs] = 2.7 x 10⁻⁴ s⁻�, 25 �C). The vast differences in the rates of acid hydrolysis can be rationalised on a steric basis. Bulkier ancillary ligands impede the direct protonation of an endo oxygen atom, or the transfer of a proton from the exo to an endo oxygen atom. The chelated bicarbonate complex [Co(trpyn)(O₂COH)]ZnCl₄�3H₂O has been synthesised and characterised by microanalysis and X-ray crystallography (orthorhombic, Pbca, a = 18.1820(66) Å, b = 14.7256(44) Å, c = 19.6344(68) Å, α = β = γ = 90�, Z = 8, R1 = 0.0435, wR2 = 0.1130). The first products of direct metallion of coordinated carbonate, under both acidic and neutral conditions, have been isolated and characterised by microanalysis and IR spectroscopy. The X-ray crystal structures of the bimetallic complexes [Co(Me-tpa)O₂COZnCl₃]�H₂O (triclinic, P-1, a = 8.262(1) Å, b = 11.290(1) Å, c = 13.766(2) Å, α = 95.314(4)�, β = 103.160(4)�, γ = 107.071(5)�, Z = 2, R1 = 0.0382, wR2 = 0.0940) and [Co(pmea)O₂COZnCl₃]�H₂O (triclinic, P-1, a = 8.2916(7) Å, b = 11.0999(11) Å, c = 14.0994(13) Å, α = 8.2916(7)�, β = 102.607(4)�, γ = 108.600(4)�, Z = 2, R1 = 0.0347, wR2 = 0.0770), and the trimetallic complex [(Co(trpyn)(O₂CO))₂Zn(H₂O)̀₄](ZnCl₄)₂�3H₂O (monoclinic, P2₁/c, a = 20.9734(17) Å, b = 17.3712(12) Å, c = 15.7635(13) Å, β = 111.376(4)�, α = γ = 90�, Z = 4, R1 = 0.0235, wR2 = 0.0517) have been obtained. In addition, the X-ray crystal structures of the complexes [Co(trpyn)(O₂CO)](Zn(OH)₂Cl₃)�4H₂O (triclinic, P-1, a = 7.4962(7) Å, b = 13.4019(11) Å, c = 13.6887(11) Å, α = 74.631(4)�, β = 82.893(4)�, γ = 82.324(4)�, Z = 2, R1 = 0.0268, wR2 = 0.0638) and [Co(tepa)(O₂CO)]₂(ZnCl₄)�3H₂O (triclinic, P-1, a = 9.9250(10) Å, b = 15.5561(13) Å, c = 15.8730(16) Å, α = 89.545(4)�, β = 85.019(5)�, γ = 72.714(4)�, Z = 2, R1 = 0.0291, wR2 = 0.0722) were obtained. These two complexes were synthesised under analogous conditions to the bi- and trimetallic complexes. However, in these cases metallation of chelated carbonate did not occur. DFT calculations have been used to calculate the relative energies of pairs of geometric isomers of [Co(N₄)(O₂CO)]⁺ complexes (N₄ = baep, abap, pmea, pmap, dppa, Me-tpa, Me₂-tpa). In all cases, except that of [Co(Me-tpa)(O₂CO)]⁺, the calculations correctly predict that the experimentally observed isomer is lower in energy. An electronic study on two series of [Co(N₄)(O₂CO)]⁺ complexes containing pyridyl (N₄ = tpa, pmea, pmap, tepa) and Me-pyridyl (N₄ = tpa, Me-tpa, Me₂-tpa, Me₃-tpa) tripodal tetraamine ligands correctly reproduces the observed trends in ⁵⁹Co NMR chemical shift and [Delta] values. A molecular orbital analysis of the two series of complexes shows that there is no significant difference between the highest energy occupied orbitals with the largest contribution from the coordinated oxygen atoms. Bond decomposition analyses of the two series of complexes indicate that there is also no difference in total bond energies. These results indicate that there is no electronic explanation for the large differences in reactivity towards acid that is observed experimentally. The first mononuclear complex containing chelated hydrogen phosphate, [Co(pmea)(O₂PO₂H)]ClO₄, has been synthesised and characterised using microanalysis, �H, ��C, ��P and ⁵⁹Co NMR, UV-vis spectroscopy and X-ray crystallography (monoclinic, P2₁/c, a = 8.7017(17) Å, b = 27.639(5) Å, c = 9.586(2) Å, β = 112.818(9)�, α = γ = 90�, Z = 4, R1 = 0.0443, wR2 = 0.1076). The X-ray crystal structure of [Co(pmeaH)(OH₂)Cl₂](CoCl₄)�H₂O (orthorhombic, P2₁2₁2₁, a = 12.6354(3) Å, b = 12.6354(3) Å, c = 15.8261(11) Å, α = β = γ = 90�, Z = 4, R1 = 0.0397, wR2 = 0.0954), in which the pmea ligand is coordinated in a hypodentate fashion, was also obtained. [Co(pmeaH)(OH₂)Cl₂](CoCl₄)�H₂O is thought to be an impurity in crude samples of [Co(pmea)Cl₂]Cl. The pK[a] of [Co(pmea)(O₂PO₂H)]⁺ was determined to be 4.99 � 0.02 by potentiometric titration. A ring inversion fluxional process, analogous to that observed for [Co(pmea)(O₂CO)]⁺, was found by VT-NMR to have a [Delta]G[double dagger] of 60 kJ mol⁻� at 35 �C. A ��P NMR spectrum, taken after the solution was left standing for approximately three hours, showed evidence of cleavage of the hydrogen phosphate chelate via a bimetallic hydrolysis mechanism. Attempts were also made to synthesise Co(III) complexes containing chelated phosphate ester ligands (monomethyl phosphate and monophenyl phosphate), with pmea as the ancillary ligand. ��P NMR spectra of the crude samples indicate that the monomethyl phosphate moiety is chelated to Co(III) (��P [delta] = 21.05 ppm). However, it is unclear whether the monophenyl phosphate is chelated or bridging between two Co(III) ions (��P [delta] = 14.36 ppm).

The results of a preliminary experiment suggested that a complexed form of cobalt was more efficacious in promoting growth of a marine phytoplankton than ionic cobalt. The phytoplankton used in this experiment was Coccolithus huxleyi, a vitamin B₁₂ producer, and the cobalt complex was cobalt (II)- ethylenediaminetetracetic acid [Co(II)- EDTA]. A review of the biochemistry of vitamin B₁₂ indicates that a B₁₂ producer might prefer, if not require, Co(III) instead of Co(II). Since some of the Co(II)-EDTA in the preliminary experiment might have become oxidized to Co(III)-EDTA, the observed stimulation of growth could have been due to Co(III)-EDTA. Two experiments were performed to determine if Co(III)-EDTA is more efficacious in stimulating growth than Co(II)-EDTA. Coccolithus huxleyi, grown in batch cultures with constant illumination, was used in both experiments. One experiment had cobalt concentrations of 10 and 1 μg/l; the other had concentrations of 1 and 0.1 μg/1. In both experiments there were no observed differences in specific growth rates between treatments of Co(III) as the EDTA complex with 10⁻⁶ M additional EDTA and Co(II) with 10⁻⁶ M EDTA. Both of these treatments resulted in a specific growth rate larger than controls without added EDTA or cobalt. It is not possible to measure the amount of Co(II)-EDTA that is oxidized to Co(III)-EDTA at the concentrations used in these experiments. Consequently these results cannot be used as a basis for rejecting the hypothesis that Co(III) is the required form of cobalt. Since Co(III)-EDTA without the additional 10⁻⁶ M EDTA was apparently able to stimulate growth in relation to the controls, it is assumed that C. huxleyi is capable of utilizing this form of cobalt. / Graduation date: 1975

Magnetism is one of material essential attributes, the different material¡¦s magnetic has been studied for many years as well as the application.The processing is smaller with recent years, and the submicro physical phenomenon adapt to more and more important. Microscopically, ferromagnetic material tend to reduce the total energy of the system, and the sample interior will response to devide several magnetic domains, however, from the article by G. Leaf et al[34], we saw the final domain structure at remanence of cobalt bar, which is not the configuration with lowest energy, is predicted from a high-field analysis of the frequencies of the standing spin waves. To further discuss this interesting phenomenon, we use the computer simulation method, and make a series of computation of cobalt disc with the various sizes and thickness. From this research, we will propose that the magnetic domain reverse process and mechanism, and also give showing relations to between the energy and the magnetic domain.

Thèse de doctorat : physique : Physique de la matière et des matériaux : Metz : 2006. / Thèse soutenue sur ensemble de travaux. Bibliogr. p.195-202.