The goals of this thesis were to improve the performance of silica polyamine composites by manipulating the surface structure and to understand the relationship between, polymer structure and ligand modification of the grafted polyamine. Improvements in silica polyamine composite performance resulted from modifying silica gel with methyltrichlorosilane (MTCS) substituted for a molar fraction of reagent chloropropyltrichlorosilane (CPTCS), which has been traditionally employed. MTCS does not possess a terminal chloride group thus preventing the subsequent attachment of a polyamine to this moiety. MTCS has a smaller molecular volume than CPTCS and as a consequence greater coverage of the silica gel surface by silanes was determined by elemental analysis and NMR. An increase in the fraction of amines not attached to the surface (free amines) allowed improved mass transfer kinetics and in some cases improvements in metal ion sorption capacities of the polymer modified materials. Further, MTCS is cheaper than CPTCS thus allowing a more economically sound synthesis. As a result of an increase in free amines, silica gel polyamine composites were modified with sodium chloroacetate and other metal selective ligands in higher yield, resulting in a material with substantially improved copper ion capacities. Silica polyamine composites have also been modified with a novel series of amino acid chelating ligands for the purpose of selective extraction of heavy metals from aqueous media. The presence of the functional groups was confirmed by 13C NMR and elemental analysis. The adsorption properties of modified composites have been determined for divalent and trivalent metal ions. Cycle testing was performed to measure longevity. Selective extraction and recovery of a single metal ion from media containing multiple metal ions has been demonstrated. The structure of the polyamine used has been shown to have a significant impact on the specific selectivity of modified silica polyamine composites even when modified with the same ligand. Potential areas of application have been tested and appear promising. These include an acid mine drainage polluted stream near Helena, MT, as well as synthetic high pressure leach laterite solutions.

<p>This thesis presents the results of investigations on the application of modern spectroscopic techniques to the characterisation of secondary bonding interactions (SBIs) in selected organo-chalcogen compounds. Although the research was mostly focused on two families of compounds, ditellurides and chalcogen-substituted azodyes, the observations and conclusions are applicable to a wide variety of compounds. Because the effects of the SBIs are subtle, great care was taken to carefully distinguish contributions from other factors. DFT computational studies showed that the molecular conformation influences the electronic excitations observable in the UV-vis spectrum and the frequency of resonance in ¹²⁵Te NMR of organoditellurides. In the absence of protection to shield the chalcogen from intermolecular interactions, the ¹²⁵Te NMR chemical shift is dependent on the concentration of ditellurides; intramolecular SBIs attenuate the concentration dependency and steric protection cancels it entirely. The nature of the solvent impacts the results of both spectroscopic techniques through several mechanisms, including the solvatochromic effect, conformational changes due to the polarity of the medium and solvation. Solution ¹²⁵Te NMR spectroscopy is sensitive to all those contributions but, for the same reason, it cannot be applied in an unambiguous way to identify the presence of SBIs.</p> <p>Conversely, the use of intramolecular SBIs to modify the spectroscopic properties of a conjugated chromophore was investigated. Push-pull azobenzenes were derivatised with functional groups containing divalent chalcogen atoms through metathesis with a mercurated derivative of the azodye. The regiochemistry of formation of the intermediate was shown to be under kinetic control. In the chalcogen-substituted molecules, the efficiency of electron delocalisation through the SBIs was assessed by calculations of the nucleus independent chemical shift (NICS). The linear (UV-vis absorption) and nonlinear (second harmonic-generation) optical responses of the modified chromophore were investigated and interpreted in the context of the SBIs. Substitution with the chalcogen groups, and the consequent perturbation of the π-system, cause a blue shift in the first absorption maxima but little change was observed in the hyperpolarisability of the chromophore ortho-functionalised with the phenylselenenyl group. The sensitivity of the electronic spectrum to the SBI was applied to monitor the process of halide exchange in the halo-chalcogenyl derivatives of the push-pull azobenzene.</p> <p>Very strong SBIs can result in interatomic distances so short that they are difficult to distinguish from hypervalent covalent bonds. This is the situation observed in the structure of the first 2,5,8,11,1,4,7,10,3,6,9,12-tetraoxatetratelluratetrazacyclododecane. DFT calculations showed that this unusual macrocycle is stable with respect to dissociation into isotellurazole oxide and VT NOESY experiments indicate it remains intact in solution.</p> / Doctor of Philosophy (PhD)

Photoelectron spectroscopy is used to investigate the electronic structure of molybdenum-molybdenum quadruple bonds in dimolybdenum tetracarboxylates. The variable energy photoelectron spectra of the valence region of dimolybdenum tetraacetate are reported for a range of incident photon energies. The pi components of the metal-metal bond contain the most molybdenum 4d character. The sigma component has contribution from both the ligand and the molybdenum 4p orbitals on the adjoining molybdenum. The delta component has significant overlap with the ligand orbitals. A comparative gas phase and surface ultraviolet photoelectron study of dimolybdenum tetrabenzoate is also reported. This is the first dimolybdenum tetracarboxylate where the ligand is capable of large resonance overlap with the metal center. There is significant orbital overlap between the ligand and the metal-metal bond, especially with the delta component. Both of these studies show that there is electronic communication between the metal-metal bond and the carboxylate ligand.

The first tris(imido) complex of a group 6 transition metal, [Li(THF)₄][W(=NAr)₃Cl] (8) (Ar = 2,6 iPr-C₆H₃) was prepared from W(=NAr)₂Cl₂(THF)₂ (2) and 2 equiv of the corresponding lithium amide, LiNHAr in THF. Complex (8) crystallizes in the monoclinic space group P2(1/n) with a = 13.787 (4) Å, b = 17.348 (5) Å, c = 22.781 (8) Å, and β = 90.43 (3)° with Z = 4. The crystal contains discrete C₃ᵥ [W(=NAr)₃Cl]⁻ anions with imido W-N-C(ipso) angles averaging 170.8 (15)° and imido W-N bonds averaging 1.782 (15) Å. The neutral imido species W(=NAr)₃(PMe₃) (15) was made by adding 10 equiv of PMe₃ to (8). "Coupling" of the imido ligand in (15) with CO₂ and O=C=NR (R = Ph, ᵗBu) gave W[NArC(O)O] (=NAr)₂ PMe₃ (20) and W[NArC(O)NR](=NAr)₂PMe₃ (19) respectively. 2,6 Diisopropylaniline was added to (8) to give the complex W(=NAr)₂(NHAr)₂ (9). The chloride ligand of complex (8) was replaced by Li alkyl reagents to yield alkylated product [Li(THF)₄][W(=NAr)₃R] (R = Me, ᵗBu and Np') (11-13). The cation of (8) was substituted by adding ⁿBu₄NBr to afford [ⁿBu₄N][W(=NAr)₃Br] (10). These and related synthetic and reactivity studies will be described.

<p> The properties of crystalline materials are controlled by their composition and by their structure, however, the structure of a crystal is only partly controlled by its composition. Development of specifically directed inorganic syntheses will require an understanding of the dynamics of crystal phase forming processes, especially those processes involved in generating specific symmetry features. One successful strategy, intended to exert synthetic control over the symmetry of crystal structures involves incorporating polar, anionic species, called basic building units (BBUs). Polar BBUs tend to adopt ordered configurations, increasing the probability that discovered structures will have polar symmetry. Discovery of eight new compounds with general formula K₁₀(M₂O_nF_11-n)X (M = V^V, Nb^V, n = 2, M = Mo^VI, n = 4; X^- = (F₂Cl)_1/3, Cl, ([Br][Br₃])_1/2, and ([I][I₃])_1/2) is reported. Post-synthetic structure analysis these compounds which crystallize in the space groups<i> P3&macr;m</i>1, <i> Pmn</i>2₁, and C2/<i>m,</i> is used to analyze and expand on the &Lambda;-shaped anionic unit strategy.</p><p> The atom scale processes involved in the phase transition are examined through computational Molecular Dynamics (MD) simulations. Atomistic MD simulations present the technical challenge of developing models for calculating interatomic interactions that can reliably reproduce experimental results. A strategy for improving the accuracy of empirical interatomic interaction models is outlined. Cryogenic temperature (~15K) and variable-pressure (1-10 GPa) diamond anvil cell single crystal diffraction experiments on the <i>Pna</i>2₁ phase of KNaNbOF₅ are used to develop a set of empirical pairwise interatomic interaction functions of the complex five element system. The atom scale dynamics of a temperature driven reconstructive phase transition in KNaNbOF₅ are examined, leading to the discovery of a dynamically disordered high temperature crystal structure, and the origin of the NCS phase stabilization upon cooling. The reconstructive transition going from the <i> P</i>4/<i>nmm</i> phase to the high temperature <i>Cmcm </i> phase is believed to result from a loss of O/F site ordering caused by rigid rotations of octahedral [NbOF₅]^2- BBUs. The high temperature phase is found to be a dynamically disordered state involving two locally stable phases in the potential energy landscape with <i> Pbcm</i> and <i>Pnma</i> space group symmetries. </p>

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The environmental behavior of the actinide elements will depend on their redox and complexation chemistries. Chapter I of this Dissertation briefly reviews actinide solution chemistry on the fundamental and applied (i.e. environmental) levels. Three projects involving the hexavalent actinides are then discussed. / Solvent extraction by thenoyltrifluoracetone was found suitable for investigation of tracer-level actinide redox reactions. This technique was employed in the study of reactions of Np(VI) with water-soluble carboxylates, phenols, and other oxygen-containing organic ligands. Results from this study are presented in Chapter II. Ligand properties necessary to effect reduction were identified as aromaticity and the presence of a hydroxy function. A rate equation for the reduction of Np(VI) by salicylate was derived which shows first order dependency on ligand and metal and inverse dependency on hydrogen ion concentration. Ligand substitution para to a phenolic group was found to slow ligand oxidation by Np(VI). Reasons for this effect are suggested. / Chapter III describes the development and characteristics of a coated-wire electrode specific for actinyl cations. The electrode was found to respond rapidly and reproducibly to 10('-5) - 10('-2) M U(VI) with a slope almost twice that predicted by the Nerst equation. Tri- and tetravalent class a cations did not interfere with uranyl detection by the electrode, but pentavalent interference was severe. Possible mechanisms for the function of the ion-sensitive membrane are suggested, and potential uses of the electrode in actinide redox studies are discussed. / The results of an investigation of the thermodynamics of Pu(VI) complexation by bicarbonate at pH 8 are presented in Chapter IV. From the previously determined 1:1 stability constant and from calorimetric data, the stability constant for formation of the 1:2 complex was estimated, and the enthalpy and entropy of formation of both complexes were determined. Based on thermodynamic cycles and comparison with literature data, PuO(,2)(OH)(HCO(,3)) and PuO(,2)(CO(,3))(,2)('2-) were proposed as structures for the 1:1 and 1:2 complexes, respectively. / Source: Dissertation Abstracts International, Volume: 42-11, Section: B, page: 4411. / Thesis (Ph.D.)--The Florida State University, 1982.

The complex formation of UO(,2)('+2), Ca('+2) and Th('+4) with halates, acetate and haloacetates has been studied by means of solvent extraction. The stability constants have been determined for UO(,2)('+2), Ca('+2) and Th('+4) with halates, acetate and haloacetates at 25(DEGREES)C. The enthalpies were determined by titration calorimetry. From the value of the enthalpy and entropy, model were developed for assignment of relative inner vs outer sphere character to the complexes. It has been found that inner sphere character increases with the charge density of the cation and with the pka of the ligands. / Source: Dissertation Abstracts International, Volume: 43-03, Section: B, page: 0719. / Thesis (Ph.D.)--The Florida State University, 1982.

Complexation of calcium and magnesium with adenosine mono, di and tri phosphates has been studied at 25(DEGREES)C and 0.1 M ionic strength. Stability constants for the complexes with unprotonated as well as the monoprotonated forms of these ligands have been determined by potentiometric technique. The enthalpy changes for the complexation reactions have been determined by titration calorimetry. / Complexation of lanthanide ions with adenosine mono and tri phosphates has been studied at 0.1 M ionic strength (NaClO(,4)). The stability constants for unprotonated and monoprotonated complexes have been determined by potentiometry and the heat of complexation have been determined by temperature dependence study of the corresponding stability constants. / Complexation of sodium ions with adenosine triphosphate has been studied to evaluate its effect on the metal complexation study. The corrections are estimated for the observed complexation constants and the thermodynamic parameters. / The studies show that the adenosine phosphates are bound to the alkaline earth cations mainly through the phosphate chain. The interaction of the base (adenine) is either not present or is negligible. The complexation of lanthanide ions by adenosine monophosphate is also mainly through the phosphate chain. However, the complexation of lanthanide ions by adenosine triphosphate is best interpreted in terms of complexation through the phosphate chain as well as the heterocyclic ring. / Source: Dissertation Abstracts International, Volume: 43-01, Section: B, page: 0134. / Thesis (Ph.D.)--The Florida State University, 1982.