<p> Thin films (~100 nm) have been prepared of the prototypical spin-crossover complex Fe(phen)₂(NCS)₂ (phen = 1,10-phenanthroline). Initial attempts to prepare these films by direct vapor deposition yielded films of a different material. Through extensive FT-IR, Raman, UV-Vis, and x-ray photoelectron spectroscopy it is shown that these as-deposited films are the ferroin-based tris complex [Fe(phen)₃](SCN)₂. Structural characterization by AFM and powder XRD reveals them to be smooth and amorphous. When heated, the [Fe(phen)₃](SCN)₂ films are converted first to Fe(phen)₂(SCN)₂ and then to a third species postulated to be Fe(phen)(NCS)₂ which is likely a one-dimensional coordination polymer. On the other hand, deposition from Fe(phen)₂(NCS)₂ onto heated substrates produces a mixture of these three materials. The identity of the Fe(phen)₂(NCS)₂ films is proved by additional spectroscopic, structural, and magnetic characterization. Magnetometry reveals them to remain spin-crossover active albeit with a more gradual and incomplete spin-transition than the bulk material. The films are found to be granular in nature and deep crevices were observed at the grain boundaries. Within the optical microscope, the coloring of the grains is seen to be dependent upon sample orientation. Powder XRD indicates texturing of crystalline domains where the crystallographic c-axis is parallel to the surface normal. This represents a new process for production of Fe(phen)₂(NCS)₂ films.</p><p> With the aim of realizing the potential for spin-crossover materials to modulate electrical conduction and vise versa, electrical characterization has been performed as a function of temperature on vertical junction devices incorporating the prepared Fe(phen)₂(NCS)₂ films. In order to prevent penetration of the top electrode through the cracks and crevices in the organometallic layer, a multiple sequential deposition and annealing process was developed to produce films with a continuous surface topography. A small change in the weak electrical conductivity of these devices appears at the spin transition temperature, demonstrating for the first time in this important material a coupling of the electrical conductivity and magnetic spin state. Here, the HS state has a higher electrical conductivity. Incorporation of LiF interfacial layers between the Fe(phen)₂(NCS)₂ and the metal electrodes improves conduction slightly but tunneling still appears to be the current-limiting mechanism. Electrical measurements were also performed on devices made with the related complex [Fe(phen)₃](SCN)₂. Such films were much more conductive&mdash;as good as other typical organic semiconductor materials. All together, this work establishes the potential for this family of complexes to be incorporated into thin-film based electrical devices whose operation is based on the spin-crossover effect or otherwise.</p>

Water pollution is a major concern worldwide. Bacteria, viruses and fungi present in drinking water cause various diseases as a result of poor hygienic conditions in developing countries. Similarly, presence of microorganisms in drinking water is a threat to public health in developing world due to poor hygienic condition. Numerous disinfectants and biocides are used for inhibiting the growth of pathogenic microbial contamination, producing carcinogenic by-products which are dangerous to human health. This work involved the synthesis, characterisation and application of novel multifunctional nanocomposites by the modification of cost effective available materials for antimicrobial treatment of contaminated water and the detection of specific DNA associated with water-borne bacteria. A series of multifunctional nanocomposites composed of commercially available carbon (activated charcoal and multi-walled carbon nanotubes), and silica-based materials such as diatomeous earth, celatom-80 and celatom-14 were modified with silver and iron oxide nanoparticles via a simple one-pot synthesis protocol in order to incorporate antimicrobial and superparamagnetic properties. The resultant materials have been tested for antimicrobial efficiency using model water system containing Gram-negative Escherichia coli (E. coli) K12 and Gram-positive Staphylococcus. aureus (S. aureus) microorganisms. It was found that all materials ranging from 10 to 200 μg/mL produced excellent inhibition of S. aureus and E. coli. All nanocomposites have been fully characterised by several physico-chemical techniques such as Transmission Electron Microscope (TEM), Scanning Electron Microscope (SEM), X-ray Fluorescence (XRF), Energy Dispersive X-ray Analysis (EDAX), Fourier Transform Infrared Spectroscopy (FT-IR), Nitrogen gas adsorption and (BET) surface area analysis. Surface area of the materials measured in range of 5 to 560 m2/gm. XRF along with EDAX/SEM analyses have been used for the confirmation of silver and iron oxide presence in the nanocomposite materials. TEM images showed nano-sized silver particles with an average diameter of 15-17 nm and iron oxide (magnetite) nanoparticles with an average diameter of 30 nm embedded into the nanocomposites. FT-IR spectroscopy measurement confirmed the presence of Fe-O bonding of iron oxide nanoparticles due to a characteristic stretching vibration at 570 cm-1. Powder X-ray Diffraction (XRD) measurements confirmed the crystalline structure of the iron oxide nanocomposite mostly magnetite (Fe3O4). Nitrogen gas adsorption-desorption experiments suggests the presence of average pore diameter 28 to 79 Å, micropore volume: 0.01 to 0.16 cm³/g, and surface area 5 to 560 m2/g. Gram-negative E. coli K12 and Gram-positive S. aureus bacteria were used for anti-bacterial activity study where the nutrient agar was used for the growth of the bacteria. The antimicrobial effect of the nanocomposites was quantified by counting the number of colonies (colony forming unit, CFU/mL) grown on the media compared with a blank solution. Different concentrations (0.2 µg/mL to 300 µg/mL) of the nanocomposite materials were used for this study. MBC of QM1-3 and QM2-3 was found 10 µg/mL for the S. aureus and 30 µg/mL for E. coli K12, while other samples of QM3-3, QM4-3 and QM5-3 were higher such as 30 µg/mL for the S. aureus and 100 to 200 µg/mL for E. coli. All experiments were performed in triplicate and the data presented are the mean values of triplicate experiments ± standard deviation. Detection of water-borne microorganisms is the second application of the developed nanocomposites via surface modification with specific oligonucleotides sequences of E. coli gene followed by hybrid capture with complementary sequence. It was observed that multi-walled carbon nanotubes, activated charcoal and diatomeous earth gave good and satisfactory results (0.384 to 0.400 nmol/mg) in hybrid capture of complementary oligonucleotides sequences in model assay. Surface modified optimum materials (carbon nanotubes and activated carbon) with efficient hybrid capture were also efficient in detecting amplicon of 97 base pairs (bp) of E. coli specific genome by PCR experiment.

<p> In this thesis I present the synthesis and characterization of materials exhibiting frustrated magnetism. In Chapter 1 I describe magnetic frustration and some of the magnetic states that can arise from it followed by the background on iridates and platinates with honeycomb structures and rare earth pyrochlores. </p><p> In Chapter 3 I discuss my work on the synthesis and properties of ternary sodium iridates with formulas Na_xM_2/3Ir_1/3O₂ and Na_xM_1/3Ir_2/3O₂ (M = Mn, Fe, Co, Ni, Cu, Zn). The ternary iridates are based on the honeycomb compound Na₂IrO₃ but show more disorder in the honeycomb layer than the parent. The six new compounds are all spin glasses but show distinct magnetic properties from one another. </p><p> In Chapter 4 I continue my work on honeycombs by exploring new ternary sodium platinates. These three new compounds with formulas Na₃MPt₂O_6+x (M = Mg, Cu, Zn) are structurally very similar to the iridates discussed in Chapter 2 but have non-magnetic Pt⁴⁺ in place of magnetic Ir⁴⁺. The Mg and Zn variants are non-magnetic while the Cu variant is paramagnetic at 2 K. </p><p> Chapter 5 is a synchrotron X-ray diffraction study of the magnetically frustrated rare earth pyrochlores Ho₂Ti₂O₇, Er₂Ti₂O₇ and Yb₂Ti₂O₇. Previous neutron scattering studies have shown reflections that are forbidden by the assigned space group <i>Fd-3m,</i> therefore high intensity, high resolution X-ray diffraction data was collected to determine if the reflections are present. Slight variations in sample stoichiometry were studied to account for possible sample variation. The forbidden reflections are absent from the X-ray diffraction patterns, providing strong evidence that the extra reflections in neutron scattering experiments are not structural in origin.</p>

Thesis (Ph.D.)--Drexel University, 2008. / Includes abstract and vita. Includes bibliographical references (leaves 438-442).

Thesis (Ph. D.)--Drexel University, 2005. / Includes abstract and vita. Includes bibliographical references (leaves 253-268).

<p> Metal&ndash;organic frameworks are a rapidly expanding family of crystalline porous materials and have shown great promise to address various challenges such as gas storage and separation due to their well-defined pore size and unprecedented tunability in both composition and pore geometry. Here, we have synthesized and structurally characterized a number of new metal- organic framework materials and studied the effects of ligands and metal types on the construction and properties of metal&ndash;organic frameworks. To probe the effects of functional groups on ligands, two zinc-based three-dimensional frameworks have been synthesized. They consist of zinc-triazolate layers pillared by dicarboxylates with different functional groups. In addition, a very unusual magnesium metal-organic framework material has been made. It consists of novel magnesium acetate chains crosslinked by 1,4-benzenedicarboxylate into a three-dimensional framework with large channels. The phase purity and structures of these materials have been determined by powder and single-crystal X-ray diffraction. Their thermal stability and sorption a properties for gas molecules such as N₂, H₂, and CO₂ have also been studied. </p><p>

Made available in DSpace on 2014-06-11T19:35:08Z (GMT). No. of bitstreams: 0 Previous issue date: 2001Bitstream added on 2014-06-13T21:07:17Z : No. of bitstreams: 1 goncalves_rr_dr_araiq.pdf: 4816799 bytes, checksum: 0ead4e8520f4bac562bdbb2a9a71bc5c (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / A preparação dos sistemas dopados com ions lantanídeos (Eu e Er): SnO2, HfO2, HfO2 disperso em matriz híbrida, SiO2-HfO2, Ta2O5, Ta2O5 disperso em matriz híbrida, através da metodologia sol gel, foi objetivo desta tese . São apresentados resultados para suspensões coloidais, sólidos (géis, xerogéis e pós) e filmes preparados por spin coating. Suspensões coloidais de SnO2 dopados com até 2% em mol de íons Eu e Er foram preparadas a partir da redispersão, em meio aquoso básico, de nanoparticulas com a superfície modificada. Diâmetro médio de 4 e 6 nm foram observados para os compostos dopados e puros respectivamente, através de espalhamento de luz e microscopia eletrônica de transmissão. Os compostos apresentam nanocristalitos, estrutura cassiterita. O íon Eu3+ ocupa dois diferentes sítios de simetria na matriz SnO2. Um referente ao ion Eu3+ na rede cristalina de SnO2, substituindo átomos de Sn4+, sítio de alta simetria (D2h, C2h) apresentando um tempo de vida de emissão do 5D0 de 6ms; e o segundo referente ao Eu3+ adsorvido na superfície da partícula apresentando um tempo de vida de emissão do 5D0 de 0,3 ms. A proteção da superfície da partícula com moléculas orgânicas, beta dicetonas, originou suspensões coloidais altamente luminescentes em meio aquoso, formando um complexo com o ion Eu3+ presente na superfície da partícula, apresentando tempo de vida de 0,6 ms. Filmes finos homogêneos e transparentes foram depositados a partir das suspensões coloidais usando spin coating. Monocamadas de até 200 nm foram depositadas, observando-se o aumento linear da espessura com a concentração de material e número de depósitos. Filmes tratados a 500oC apresentam nanocristalitos de 10nm, estrutura cassiterita. Os filmes apresentam alto índice de refração e uma porosidade de 26% foi calculada. Guias... / The preparation of the systems doped with lanthanide ions (Eu3+ and Er3+): SnO2, HfO2, organic-inorganic hybrid system containing HfO2, SiO2- HfO2, Ta2O5 and organic-inorganic hybrid system containing Ta2O5, by using the sol gel process, have been the aim of this work. The Results of the colloidal suspension, solids (gel, xerogel and powder) and films are presented. Luminescent SnO2 colloidal suspension, with Eu3+ and Er3+ up to 2 mol%, have been prepared by redispersion of the powder (nanoparticles with modified surface) in a basic aqueous solution. Average diameter of 4 and 6nm were observed to the compounds doped and pure respectivelly, by dynamic light scattering and high resolution transmission electron microscopy. Cassiterite structure is attributed to the crystalline phase of the nanoparticles. Eu3+ ions occupied two different symmetry site. One of them corresponds to the ion in the cassiterite structure, substituting the Sn4+ ions , high symmetry site (D2h or C2h), with a 5D0 lifetime of 6ms; and the second one corresponds to the adsorbed ions on the surface, with a 5D0 lifetime of 0,3 ms. The presence of Eu3+ ions at the surface of the particles hinder their growing and also has allowed the preparation of new materials consisting of water redispersable powders coated with Eu3+-beta diketonate complex. Enhanced UV excited photoluminescence was observed in water. Homogeneous and transparent films were deposited by using the colloidal suspension by spin coating technique. Monolayers up to 200nm were prepared and a linear increase of the thickness value were observed with the concentration of the material and also the number of the layers. Films heat treated at 5000C show nanocrystals of 10nm, cassiterite structure. High ...(Complete abstract, click electronic access below)

Orientador: Sidney José Lima Ribeiro / Banca: Norberto Aranha / Banca: Leandro Tessler / Banca: Luis A. Carlos / Banca: Verónica Zéa Bermudez / Resumo: A preparação dos sistemas dopados com ions lantanídeos (Eu e Er): SnO2, HfO2, HfO2 disperso em matriz híbrida, SiO2-HfO2, Ta2O5, Ta2O5 disperso em matriz híbrida, através da metodologia sol gel, foi objetivo desta tese . São apresentados resultados para suspensões coloidais, sólidos (géis, xerogéis e pós) e filmes preparados por spin coating. Suspensões coloidais de SnO2 dopados com até 2% em mol de íons Eu e Er foram preparadas a partir da redispersão, em meio aquoso básico, de nanoparticulas com a superfície modificada. Diâmetro médio de 4 e 6 nm foram observados para os compostos dopados e puros respectivamente, através de espalhamento de luz e microscopia eletrônica de transmissão. Os compostos apresentam nanocristalitos, estrutura cassiterita. O íon Eu3+ ocupa dois diferentes sítios de simetria na matriz SnO2. Um referente ao ion Eu3+ na rede cristalina de SnO2, substituindo átomos de Sn4+, sítio de alta simetria (D2h, C2h) apresentando um tempo de vida de emissão do 5D0 de 6ms; e o segundo referente ao Eu3+ adsorvido na superfície da partícula apresentando um tempo de vida de emissão do 5D0 de 0,3 ms. A proteção da superfície da partícula com moléculas orgânicas, beta dicetonas, originou suspensões coloidais altamente luminescentes em meio aquoso, formando um complexo com o ion Eu3+ presente na superfície da partícula, apresentando tempo de vida de 0,6 ms. Filmes finos homogêneos e transparentes foram depositados a partir das suspensões coloidais usando spin coating. Monocamadas de até 200 nm foram depositadas, observando-se o aumento linear da espessura com a concentração de material e número de depósitos. Filmes tratados a 500oC apresentam nanocristalitos de 10nm, estrutura cassiterita. Os filmes apresentam alto índice de refração e uma porosidade de 26% foi calculada. Guias ...(Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The preparation of the systems doped with lanthanide ions (Eu3+ and Er3+): SnO2, HfO2, organic-inorganic hybrid system containing HfO2, SiO2- HfO2, Ta2O5 and organic-inorganic hybrid system containing Ta2O5, by using the sol gel process, have been the aim of this work. The Results of the colloidal suspension, solids (gel, xerogel and powder) and films are presented. Luminescent SnO2 colloidal suspension, with Eu3+ and Er3+ up to 2 mol%, have been prepared by redispersion of the powder (nanoparticles with modified surface) in a basic aqueous solution. Average diameter of 4 and 6nm were observed to the compounds doped and pure respectivelly, by dynamic light scattering and high resolution transmission electron microscopy. Cassiterite structure is attributed to the crystalline phase of the nanoparticles. Eu3+ ions occupied two different symmetry site. One of them corresponds to the ion in the cassiterite structure, substituting the Sn4+ ions , high symmetry site (D2h or C2h), with a 5D0 lifetime of 6ms; and the second one corresponds to the adsorbed ions on the surface, with a 5D0 lifetime of 0,3 ms. The presence of Eu3+ ions at the surface of the particles hinder their growing and also has allowed the preparation of new materials consisting of water redispersable powders coated with Eu3+-beta diketonate complex. Enhanced UV excited photoluminescence was observed in water. Homogeneous and transparent films were deposited by using the colloidal suspension by spin coating technique. Monolayers up to 200nm were prepared and a linear increase of the thickness value were observed with the concentration of the material and also the number of the layers. Films heat treated at 5000C show nanocrystals of 10nm, cassiterite structure. High ...(Complete abstract, click electronic access below) / Doutor

<p> &beta;-Diketones are well known to form metal complexes with practically every known metal and metalloid. Metal complexes of fluorinated &beta;-diketones generally exhibit increased volatility and thermal stability compared to the non-fluorinated analogues, and thus are used extensively in various chemical vapor deposition (CVD) processes for the deposition of metal, simple or mixed metal oxides, and fluorine-doped metal oxide thin films. Furthermore, the electron-withdrawing nature of the fluorinated ligand enhances the Lewis acidity of a coordinatively unsaturated metal center which facilitates additional coordination reactions. The physical and structural properties of fluorinated &beta;-diketonate complexes are discussed in Chapter 1 and a few key application examples are given.</p><p> The focus of this work is the synthesis and single crystal X-ray structural characterization of unsolvated and coordinatively unsaturated metal complexes of bis(pentafluorobenzoyl)- methanide (L, C₆F₅COCHCOC₆F₅^-). In Chapter 2, we present the preparation and isolation of the unsolvated complex [Cu(L)₂] in pure crystalline form for the first time. We subsequently investigated the reaction of unsolvated [Cu(L)₂] with sodium hexafluoroacetylacetonate [Na(hfac)] in a solvent-free environment. This reaction allowed the isolation of the first heterometallic Na&ndash;Cu diketonate [Na₂Cu₂(L)₄(hfac)₂] structurally characterized by single crystal X-ray crystallography. Thermal decomposition of [Na₂Cu₂(L)₄(hfac)₂] was investigated for its potential application in MOCVD processes. In the final chapter, we present the first exploration of the anhydrous synthesis of Co(II) complexed with bis(pentafluorobenzoyl)methanide in order to produce a complex without ligated water. Single crystal X-ray crystallographic investigations revealed the isolation of the ethanol adduct, [Co₂(L)₄(C₂H₅OH)₂], and following the removal of ethanol, a 1,4-dioxane adduct, [{Co₂(L)₄}₂(C₄H₈O₂)]. </p><p> In this work, we have provided the first investigation of the synthesis, isolation and single crystal X-ray structural characterization of unsolvated and coordinatively unsaturated Cu(II) and Co(II) complexes of bis(pentafluorobenzoyl)methanide ligand. These studies demonstrate how the electrophilicity of a coordinatively unsaturated metal complexed to highly-fluorinated &acirc;-diketone ligands can be utilized for the formation of new adducts or new and interesting heterometallic complexes. This body of work provides a basis upon which future research into unsolvated and unligated bis(pentafluorobenzoyl)methanide metal complexes can expand.</p><p>

<p> In the past, we have demonstrated that 1,8-anthraquinone-18-crown-5 (1) and its heterocyclic derivatives act as luminescent hosts for a variety of cations of environmental and clinical concern. We report here a series of heteroatom-substituted macrocycles containing an anthraquinone moiety as a fluorescent signaling unit and a cyclic polyheteroether chain as the receptor. Sulfur, selenium, and tellurium derivatives of 1,8-anthraquinone-18-crown-5 (<b>1</b>) were synthesized by reacting sodium sulfide (Na₂S), sodium selenide (Na₂Se) and sodium telluride (Na₂Te) with 1,8-bis(2-bromoethylethyleneoxy)anthracene - 9,10-dione in a 1:1 ratio (<b>2,3,</b> and <b>6</b>). These sensors bind metal ions in a 1:1 ratio (<b>7</b> and <b>8</b>), and the optical properties of the new complexes were examined and the sulfur and selenium analogues show that selectivity for Pb(II) is markedly improved as compared to the oxygen analogue <b>1</b> which was competitive for Ca(II) ion. </p><p> Selective reduction of <b>1</b> yields secondary alcohols where either one or both of the anthraquinone carbonyl groups has been reduced (<b> 15</b> and <b>9</b>). A new mechanism for the fluorescence detection of metal cations in solution is introduced involving a unique keto-enol tautomerization. Reduction of <b>1</b> yields the doubly reduced secondary alcohol, <b> 9. 9</b> acts as a chemodosimeter for Al(III) ion producing a strong blue emission due to the formation of the anthracene fluorophore, <b>10,</b> via dehydration of the internal secondary alcohol in DMSO/aqueous solution. The enol form is not the most thermodynamically stable form under these conditions however, and slowly converts to the keto form <b>11.</b> </p><p> Currently we are focusing on cucurbituril derivatives, also described as molecular clips due to their folded geometry used as molecular recognition hosts. We first investigated the synthesis and characterization of aromatic methoxy/catechol terminated cucurbituril units that act as hosts for small solvent molecules, such as CH₂Cl₂, CH₃CN, DMF, and MeOH, through dual pi&hellip;H-C T-shaped interactions. We have calculated the single-point interaction energies of these non-covalent interactions and compared them to the dihedral angle formed from the molecular clip. We have also synthesized a molecular clip that contains terminal chelating phenanthroline ligands. This tetradentate ligand shows 2:3 metal:ligand binding with Fe(II) and 1:2 metal:ligand binding with Co(II) and Ni(II) cations.</p><p>