Les Polyoxométallates (POMs) sont obtenus par acidification d'une solution contenant des oxoanions [MOx]ⁿ⁻. L'élément M se trouve dans son plus haut degré d'oxydation et représente, d'une façon générale, un atome de tungstène, de molybdène, de vanadium, de niobium, ou de plus en plus des éléments nobles, tels que le palladium ou l'or. Ces espèces représentent un énorme potentiel, tant leurs propriétés en termes de taille, forme et composition peuvent être variables. Les dimensions de certaines structures peuvent dépasser plusieurs dizaines d'angström. Enfin, les POMs sont reconnus comme de véritables réservoirs d'électrons. Selon leur état de réduction, ils font office de donneur ou d’accepteur dans des processus d'échanges réversibles d'électrons. L'ensemble de ces propriétés (structurales, composition atomique, électrochimiques, physico-chimiques) en fait d'excellents candidats pour l'élaboration de systèmes électro-catalytiques. Les POMs constituent donc des nano-objets privilégiés pour des études de mécanismes réactionnels en électrochimie. Une étape nécessaire de ce travail consistera donc en la caractérisation électrochimique des POMs pour en déduire leurs possibilités en électro-catalyse. Les études effectuées en solution par toutes les techniques classiques de l'électrochimie sont également possibles à l'état solide avec l'apport de techniques complémentaires. En effet, les POMs peuvent être utilisés également pour modifier les surfaces d'électrodes auxquelles ils peuvent conférer des propriétés catalytiques remarquables vis-à-vis de divers substrats. A titre d'exemple, la fabrication d'électrodes modifiées par des POMs, selon des techniques variées (adsorption, dépôt électrolytique, confinement dans un polymère conducteur ou non, confinement par procédé sol-gel ou procédé couche par couche) conduit à l'étude fondamentale de la propagation de charges dans des films, et est réalisée en couplant l'électrochimie et la microbalance à cristal de quartz. En résumé, l'investigation systématique des propriétés électrochimiques de nouvelles molécules de POMs en vue d'applications en électro-catalyse constitue l'ossature de ce projet. Les systèmes les plus prometteurs seront sélectionnés et l'accent sera mis sur le développement de dispositifs efficaces dans la réduction du dioxygène et des oxydes d'azote et la production de l'hydrogène notamment. / Polyoxometalates (POMs) are metallic oxides obtained upon acidification of a solution containing oxoanions [MOx]ⁿ⁻. The metal element M is in its highest oxidation state and often consists of an atom of tungsten, molybdenum, vanadium or niobium, and more recently noble metal atoms such as palladium or gold. These species have an enormous potential, since their properties such as size, shape and composition may be varied. POMs are considered as electron reservoirs, and depending on their oxidation state, they may behave either as electron donors or as electron acceptors in reversible electron transfer processes, often coupled to proton exchange. Taken together, these properties (structural, elemental composition, electrochemical, physico-chemical) render them excellent candidates to obtain electro-catalytic systems and privileged entities for the study of reaction mechanisms in electrochemistry. One of the major purposes of this work is the electrochemical characterisation of new POM species in order to assess their potential applications in electro-catalysis. Studies carried out in solution by any conventional technique of electrochemistry are also possible in the solid state with the addition of complementary techniques. Indeed, POMs can also be used to modify the electrode surfaces to which they may impart remarkable catalytic properties towards various substrates. For example, the manufacture of POM-modified electrodes, according to various techniques (adsorption, electroplating, confinement in a conductive polymer or not, containment by sol-gel processes or by layer-by-layer procedures) allows to carry out fundamental studies of charge transfer in films, which is achieved by coupling electrochemistry with the quartz crystal microbalance. In summary, the systematic investigation of the electrochemical properties of new molecules of POMs for applications in electro-catalysis is the backbone of this project. The most promising systems will be selected and the focus will be on developing effective devices for the reduction of oxygen and nitrogen oxides and for the production of hydrogen in particular.

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Les polyoxométallates suscitent un intérêt de plus en plus grand et ceci dans des domaines d’applications variés. Nous avons synthétisé quatre nouvelles familles organiques de polyoxométallates utilisables en catalyse et en biochimie. Différentes séries d’hybrides covalents ont en effet été isolés et utilisés en tant que catalyseurs dans diverses transformations chimiques. Comme des réactions d’oxydations d’alcools (pour les Organo-POMs sandwich), des réactions d’additions conjuguées (pour les Organo-POMs squaramides), des réductions de quinoléines (pour les Organo-POMs diol-Amides) ou encore des réactions one-Pot d’allylation-Oxydation (pour les Organo-POMs palladium). Par ailleurs, l’étude RMN d’hybrides POMs / peptides a permis de démontrer le repliement des ligands polyglycines autour du POM via liaisons hydrogènes. L’étude par spectrométrie de masse des hybrides POMs / protéines a quant à elle permis de démontrer une interaction sélective et certainement covalente entre un hybride diazirine et le Cytochrome C. / Polyoxometalates attracting interest of more and more and this in various fields of applications. We synthesized four new families of organic polyoxometalates useful in catalysis and biochemistry. Indeed, different covalent hybrid have been isolated and used as catalysts in various chemical transformations. In oxidation reactions of alcohols (for Organo-POMs sandwich), in conjugate addition reactions (for Organo-POMs squaramides), in reductions of quinolines (for Organo-POMs diol-Amide) or in a one-Pot allylation-Oxidation reactions (for Organo- POMs palladium). In addition, NMR studies of hybrid POMs / peptides demonstrated folding of the polyglycines ligand around the POM via hydrogen bonds. The mass spectrometric study of hybrid POMs / protein demonstrated selective and certainly covalent interaction between a diazirin hybrid and Cytochrome C.

Doctor of Philosophy / Department of Chemistry / Eric A. Maatta / Polyoxometalates are self-assembled metal-oxygen anionic clusters formed primarily by Mo, W and the Group V transition metals. Their structural, chemical and physical diversity have attracted much attention from fields such as catalysis, imaging, magnetic materials, medicine and photochromism. While many of these inorganic systems are easy to prepare, their conversion to hybrid inorganic-organic materials through functionalization is an ongoing challenge. Two approaches used for functionalization involve the insertion of metal-nitrido fragments into a lacunary polyoxometalate or the direct replacement of the terminal oxo ligands with the isoelectronic organoimido [NR][superscript]2-, hydrazido [NNR[subscript]2][superscript]2-, nitrosonium [NO][superscript]+ and diazenido [NNR][superscript]+ ligands. The later process has been proven successful with a variety of different nitrogenous ligands. One of our group's goals has been to synthesize a functionalized hexamolybdate species capable of metal coordination, with the ultimate goal of forming self-assembled networks. However, previous results have been unsuccessful due to the electron withdrawing effect of the cluster which is transmitted to the metal binding site. In order to overcome this effect, several new organoimido delivery reagents (phosphineimines, isocyanates and arylamines) containing electron donating substituents have been synthesized and characterized. Attempts to attach these species to hexamolybdate are described. The synthesis and characterization of biarylimido ligands bearing remote σ-donor functionalities and their incorporation into the hexamolybdate cluster will be described. A new and exciting avenue of polyoxometalate chemistry will be demonstrated through the successful metal coordination of the biarylimido functionalized hexamolybdate to a ruthenium(II) metalloporphyrin. This also brings the hexamolybdate polyoxometalate one step closer to being capable of forming the supramolecular architectures mentioned earlier. A chromium(V) nitrido polyoxometalate has been synthesized and characterized from a lacunary Keggin precursor, in collaboration with our colleagues in Paris. The ability of this complex as a nitrogen transfer reagent will be explored. An alternative synthetic route to the osmium-nitrido-Dawson species, [(OsN)P[subscript]2W[subscript]17O[subscript]61][superscript]4- will also be described. These nitrido species could be an entry point to other derivatives through reactions with various nucleophiles and electrophiles.

Neste trabalho, filmes híbridos produzidos pela técnica da automontagem eletrostática camada-por-camada foram preparados usando-se Polioxometalatos do tipo Keggin, ácido fosfotúngstico (HPW) e o complexo monolacunar K(TPA)4[PW11O39Mn(OH2)] alternados via um polímero catiônico, poli(cloreto de alilamônio) (PAH). O filme que continha uma pré-camada de adsorção de PDMS, juntamente com 5 bicamadas de PAH e HPW apresentou um melhor comportamento eletroquímico em filmes formados sobre óxido de índio e estanho (ITO). Em função disso, este filme foi caracterizado através de Espectroscopias de Absorção na região do Ultra-Violeta Visível (UV-vis), de Absorção-Reflexão na Região do Infra-vermelho (FT-IRRAS) e de Ressonância de Plásmons de Superfície (SPR). Foi constatado por FT-IRRAS que parte da camada de PDMS está se difundindo para a superfície quando as bicamadas de PAH e HPW vão sendo preparadas. Imagens de Microscopia Eletrônica de Varredura com Emissão de Campo (MEV-EC) confirmam esta hipótese. Espectroscopia de SPR indicou que tanto a adsorção de PAH quanto a de HPW ocorrem em tempos curtos. Experimentos de Voltametria Cíclica com [Fe(CN)6]3-mostraram que este filme é poroso. Resultados de Espectroscopia de Fotoelétrons Excitados por Raios X (XPS) comprovaram que PDMS protege o substrato contra corrosão. Esse mesmo filme pôde ser utilizado numa aplicação de caráter ambiental. Ele foi capaz de detectar melamina e atrazina em concentrações 4.10-8 mol.L-1 e 1.10-6 mol.L-1 respectivamente. Filmes contendo 5 bicamadas de PAH e K(TPA)4[PW11O39Mn(OH2)] mostraram comportamentos similares referentes à queda da eletroatividade para arquiteturas iniciadas com PAH e PDMS. O filme com 5 bicamadas de PAH e K(TPA)4[PW11O39Mn(OH2)] iniciado com PAH não mostrou comportamento eletrocatalítico para a oxidação de triazinas. / In this work, self-assembled hybrid layer-by-layer films were prepared using Keggin type polyoxometalates, phosphotungstic acid (HPW) and the monolacunary complex K(TPA)4[PW11O39Mn(OH2)] alternated by a cationic polymer, poly(allylamine hydrochloride) (PAH). The film containing 5 bilayers of PAH and HPW deposited on a PDMS cushion exhibited better electrochemical behavior onto indium tin oxide (ITO) electrodes. So, this film was characterized by UV-vis spectroscopy, Fourier transformed infrared reflection adsorption spectroscopy (FT-IRRAS) and Surface Plasmon Resonance Spectroscopy (SPR). FT-IRRAS results showed that PDMS is going to the top of the bilayers of PAH and HPW when the film is prepared. Images of the Scanning Electronic Microscopy with field emission guns (FEG-SEM) confirm this fact. SPR spectroscopy results showed adsorption times of PAH and HPW short. Cyclic Voltammetry experiments with [Fe(CN)6]3- for the film confirm that it is porous. X-Ray Photoelectron spectroscopy (XPS) proved that in this film PDMS is present and it is responsible by protection against corrosion of substrate. This film can be used for environmental application. It was able to detect melamine and atrazine in concentrations of 4.10-8 and 1.10-6 mol.L-1 respectively. Films containing 5 bilayers of PAH and K(TPA)4[PW11O39Mn(OH2)] exhibited similar electrochemical behaviors for the decrease in the electroactivity for cushions of PAH and PDMS. The film with 5 bilayers of PAH and K(TPA)4[PW11O39Mn(OH2)] with PAH cushion does not exhibited electrocatalytic behavior for oxidation of triazines.

Thesis (Ph. D.)--Florida State University, 2004. / Advisors: Dr. Naresh Dalal, Dr. Johan van Tol, Florida State University, Arts and Sciences, Dept. of Chemistry and Biochemistry. Title and description from dissertation home page (viewed Jan. 18, 2005). Includes bibliographical references.

Neste trabalho, filmes híbridos produzidos pela técnica da automontagem eletrostática camada-por-camada foram preparados usando-se Polioxometalatos do tipo Keggin, ácido fosfotúngstico (HPW) e o complexo monolacunar K(TPA)4[PW11O39Mn(OH2)] alternados via um polímero catiônico, poli(cloreto de alilamônio) (PAH). O filme que continha uma pré-camada de adsorção de PDMS, juntamente com 5 bicamadas de PAH e HPW apresentou um melhor comportamento eletroquímico em filmes formados sobre óxido de índio e estanho (ITO). Em função disso, este filme foi caracterizado através de Espectroscopias de Absorção na região do Ultra-Violeta Visível (UV-vis), de Absorção-Reflexão na Região do Infra-vermelho (FT-IRRAS) e de Ressonância de Plásmons de Superfície (SPR). Foi constatado por FT-IRRAS que parte da camada de PDMS está se difundindo para a superfície quando as bicamadas de PAH e HPW vão sendo preparadas. Imagens de Microscopia Eletrônica de Varredura com Emissão de Campo (MEV-EC) confirmam esta hipótese. Espectroscopia de SPR indicou que tanto a adsorção de PAH quanto a de HPW ocorrem em tempos curtos. Experimentos de Voltametria Cíclica com [Fe(CN)6]3-mostraram que este filme é poroso. Resultados de Espectroscopia de Fotoelétrons Excitados por Raios X (XPS) comprovaram que PDMS protege o substrato contra corrosão. Esse mesmo filme pôde ser utilizado numa aplicação de caráter ambiental. Ele foi capaz de detectar melamina e atrazina em concentrações 4.10-8 mol.L-1 e 1.10-6 mol.L-1 respectivamente. Filmes contendo 5 bicamadas de PAH e K(TPA)4[PW11O39Mn(OH2)] mostraram comportamentos similares referentes à queda da eletroatividade para arquiteturas iniciadas com PAH e PDMS. O filme com 5 bicamadas de PAH e K(TPA)4[PW11O39Mn(OH2)] iniciado com PAH não mostrou comportamento eletrocatalítico para a oxidação de triazinas. / In this work, self-assembled hybrid layer-by-layer films were prepared using Keggin type polyoxometalates, phosphotungstic acid (HPW) and the monolacunary complex K(TPA)4[PW11O39Mn(OH2)] alternated by a cationic polymer, poly(allylamine hydrochloride) (PAH). The film containing 5 bilayers of PAH and HPW deposited on a PDMS cushion exhibited better electrochemical behavior onto indium tin oxide (ITO) electrodes. So, this film was characterized by UV-vis spectroscopy, Fourier transformed infrared reflection adsorption spectroscopy (FT-IRRAS) and Surface Plasmon Resonance Spectroscopy (SPR). FT-IRRAS results showed that PDMS is going to the top of the bilayers of PAH and HPW when the film is prepared. Images of the Scanning Electronic Microscopy with field emission guns (FEG-SEM) confirm this fact. SPR spectroscopy results showed adsorption times of PAH and HPW short. Cyclic Voltammetry experiments with [Fe(CN)6]3- for the film confirm that it is porous. X-Ray Photoelectron spectroscopy (XPS) proved that in this film PDMS is present and it is responsible by protection against corrosion of substrate. This film can be used for environmental application. It was able to detect melamine and atrazine in concentrations of 4.10-8 and 1.10-6 mol.L-1 respectively. Films containing 5 bilayers of PAH and K(TPA)4[PW11O39Mn(OH2)] exhibited similar electrochemical behaviors for the decrease in the electroactivity for cushions of PAH and PDMS. The film with 5 bilayers of PAH and K(TPA)4[PW11O39Mn(OH2)] with PAH cushion does not exhibited electrocatalytic behavior for oxidation of triazines.

Doctor of Philosophy / Department of Chemistry / Eric A. Maatta / Polyoxometalates have attracted much attention over the last few decades and have been studied in a wide variety of fields such as catalysis, medicine, imaging, photochromism, and magnetic materials. While many of these systems are easy to prepare, the ability to functionalize polyoxometalates is an ongoing challenge. Two approaches used to functionalize polyoxometalates involve insertion of metal fragments into a lacunary polyoxometalate or the direct replacement of terminal oxo ligands with the isoelectronic organoimido ligand. This process has been proven successful in many cases and with a wide variety of organoimido compounds. One of our group’s goals has been to synthesize a functionalized hexamolybdate species that is capable of metal coordination. However, previous results have been hindered because the electron withdrawing effect of the cluster is transmitted to the metal binding sites. In order to combat the electron withdrawing effect of the cluster, 4-amino piperidine dithiocarbamate ligands, which have no conjugation in the ring and are capable of metal binding, have been synthesized and characterized. A series of transition metal complexes have been made and a single crystal has been grown of a nickel(II) complex. Attempts to attach these species to clusters are described. Imido hexamolybdate clusters have been functionalized with styryl and iodophenyl groups. The styrene functionalized hexamolybdate was copolymerized with 4- chloromethylstyrene in moderate yields. This copolymer has the capabilities for further substitution at the chloromethyl group. The iodophenyl functionalized hexamolybdate was fully characterized including a single-crystal X-ray structural determination. This functionalized hexamolybdate can be used in carbon-carbon bond formation through coupling reactions. A chromium(V) nitrido polyoxometalate has been synthesized from a lacunary Keggin precursor and characterized. This nitrido species shows promise as a nitrogen transfer agent. Likewise, this nitrido species could be an entry point to other derivatives through reactions with various nucleophiles and electrophiles.

No description available.