Dissertations / Theses on the topic 'Mixed valence'

A series of dimolybdenum compounds having a Mo2 4+ core coordinated by various ligands, including formamidinate (e.g. DAniF = N, NN-di-p-ansisylformamidinate ), acetate and/or acetonitrile molecules, have been synthesized as building blocks for the construction of Mo2-containing supramolecular arrays. Compound Mo2(DAniF)3(O2CCH3) was specifically designed for the preparation of dimolybdenum pairs, whereas the others meet the needs of Mo2 4+ units for different geometry settings. Compounds described by a general formula [Mo2]L[Mo2], where [Mo2] = [Mo2(DAniF)3]+, have two dimetal units electronically coupled by the central unit L , which consequently engender significant impact on the redox property and electronic structure of the molecule. It is found that in the weakly coupled complex system, [Mo2]M(OCH3)4[Mo2] (M = Zn and Co), the mixed-valence complexes present asymmetric molecular structures with two distinct [Mo2] units corresponding to be a bond order 4.0 (F2B4*2) and 3.5 (F2B4*1), respectively. EPR and magnetic susceptibility measurements for the doubly oxidized species show that there is no significant antifferromagnetic spin coupling. Electron delocalization occurs in the complex system where a N, N'-dimethyloxamidate binds two [Mo2] units within two fused six-membered rings. In this case, the mixed-valence complex has a symmetric molecular structure, implying that the odd electron is fully delocalized over two [Mo2]units. Strong metal-metal interaction is also evidenced by intervalence charge transfer of the mixed-valence species and the diamanetism of the doubly oxidized complex. Remarkably, two isomers varying in linkage conformation, namely, alpha and beta, have been isolated as diaryloxamidate ligands are used as the linker. Studies on the neutral and the oxidized compounds of the two isomers by employing various techniques consistently show that in the alpha form intramolecular electron transfer is blocked , while in the beta form, the electrons are delocalized over the two [Mo2] units. Thus, the mixed-valence complexes of the two isomers are appropriately described by alpha-[Mo2]0(oxamidate)[Mo2]1+ and beta- [Mo2]0.5+(oxamidate)[Mo2]0.5+ respectively.

The work presented in this dissertation details a systematic study of the fundamental and applied properties of electroactive metal-organic framework (MOF) materials from first design principles utilising a combined structural, electrochemical, spectroelectrochemical and computational approach. The structure-property relationships arising from the incorporation of organic-based electroactive ligands, specifically topology-driven through-space charge transfer and radical delocalisation, into a series of 3-dimensional MOF materials were investigated from both a fundamental and applied perspective. Chapter 3 details the fundamental study of a previously unreported method of charge transfer in MOF materials focused on through-space intervalence charge transfer (IVCT). Two novel ligands, BPPTzTz and BPPFTzTz, incorporating the electron accepting thiazolo[5,4-d]thiazole (TzTz) moiety were synthesised and extensively characterised. The structure-property relationships within these materials enabled the access of a topology characterised by close proximity of cofacially stacked TzTz ligands. Reduction of the TzTz ligands of these frameworks led to the formation of a mixed-valence material exhibiting unusual IVCT properties that could be accessed in situ electrochemically or ex situ via chemical reduction. The mixed-valence properties demonstrated by these materials were extensively characterised by using a variety of electrochemical, spectroelectrochemical and computation techniques to derive a mechanism by which this through-space IVCT operates. Radical anion spin delocalisation and its effects on spin state switching is the focus of Chapter 4 concerning the synthesis of an Fe2+ spin crossover (SCO) Hofmann material incorporating the redox-active DPTzTz ligand. An extensive structural, electrochemical, spectroelectrochemical and computational study was carried out on this framework in addition to studies of its magnetic properties. The structure was found to exhibit an abrupt, single-step SCO transition from high spin (HS) to low spin (LS) Fe2+ upon cooling. The structural changes upon desolvation of the de novo structure was extensively characterised using single crystal X-ray diffraction which revealed a series of irreversible structural phase transitions. The SCO properties of the desolvated material were characterised by an incomplete, single-step transition with hysteresis widths comparable with the highest reported in three-dimensional Hofmann materials. The framework was found to successfully retain the electrochemical properties of the discrete DPTzTz ligand upon self-assembly and using chemical reduction, the SCO properties of the material were successfully modified relative to the neutral parent phase. The results of this study demonstrated the successful application of a previously unreported method of modifying the magnetic properties of a solid state SCO material. An applied study of an electroactive MOF targeting gas sorption applications is the focus of Chapter 5, detailing a topological analogue of the well-known MOF-74 material incorporating the electron accepting DSNDI ligand. The neutral parent phase was characterised using a variety of electrochemical, spectroelectrochemcial and computational methods which demonstrated a porous MOF stable to both electrochemical and chemical reduction. The gas sorption properties of this framework, which contained open metal sites upon activation, were investigated with respect to H2, CH4 and CO2. Chemical reduction of this material yielded a material containing ligand-based radical anions and Li+ counterions; the sorption properties were successfully retained, however a significant enhancement of the CO2 isosteric heat of adsorption was observed. The enhanced CO2 binding enthalpy of ~45.0 kJ/mol was comparable to the highest performing member of the parent MOF-74 series and was found to be a promising candidate as a CO2 sorbent material. Fundamental studies of this material were also carried out with respect to its ability to form donor-acceptor (D-A) units within the solid state structure. A series of six electron donating molecules were infiltrated into the structure upon which donor-acceptor pairs were successfully established. The resulting D-A MOFs were characterised ex situ using UV-Vis-NIR and EPR spectroscopies which confirmed the presence of radical species and D-A charge transfer within the structure. DFT calculations were performed to further elucidate the nature of these D-A interactions with the degree of partial charge transfer also examined via these methods. The successful formation of donor-acceptor complexes in the framework structure demonstrated a strategy by which the conductive and sorption properties of the material might be modified by careful choice and energy level matching of guest electron donor with the electron accepting DSNDI ligands of the bulk framework. This work has demonstrated a series of multifunctional MOF materials with novel properties accessible by virtue of their intrinsic redox capabilities. Insight into the electronic properties of MOF materials and their corresponding structure-property relationships has been achieved with exciting results demonstrated. The fundamental investigations here serve as an invaluable platform for the development of future multifunctional electroactive MOF materials targeting commercial and industrial applications.

A series of conformationally constrained 2,6-bisferrocenylphenyl thioethers were synthesized via Suzuki-Miyaura cross coupling reactions. Structural information was obtained using X-ray crystallography and dynamic ¹H NMR spectroscopic studies, showing highly constrained m-terphenyl systems. Interaction of the ferrocene moieties through space mediated by the sulfur were studied by ultra-violet photoelectron spectroscopy (UPS), cyclic voltammetry, differential pulse voltammetry, UV-Vis-NIR spectroscopy and DFT computations. Electrochemical results show two, fully reversible 1e⁻ redox processes for the ferrocenes where the separation of peaks is affected by both solvent and supporting electrolyte, suggesting significant electrostatic interaction which is further confirmed in the gas phase by UPS studies. To determine if these interactions could be observed at greater distances, extended m-terphenyl complexes were shown in which 2-sulfur and 3-aromatic moieties were synthesized using a developed selective Suzuki-Miyaura monocoupling procedure in good yields. In these systems, interaction was not observed by electrochemistry or UPS. This suggests the distance between redox centers (~16 Å) is too great for electrostatic interaction, even though there is enhanced interactions observed in the truncated systems. Two new bisferrocenylphenylsulfoxides were also synthesized and studied to determine the effect of the polar sulfoxide bond on through space interaction between the ferrocene moieties. The electronic and redox properties of these compounds were studied by ultra-violet photoelectron spectroscopy, cyclic voltammetry, differential pulse voltammetry, and DFT computations. Electrochemical results for 2,6-bis(ferrocenyl) thioanisole S-oxide show two, fully reversible one electron redox processes. The initial oxidation shows a 62 mV negative shift compared to the sulfide analog 2,6-bis(ferrocenyl)thioanisole, and an increased peak separation for the oxidations of 160 mV. No peak separation is observed in the extended sulfoxide system. No intervalence charge transfer band was observed in the truncated sulfoxide complex by monitoring the UV-Vis/NIR spectroscopy of the mixed valence complex, ruling out electronic communication. Thus, the through space electrostatic interactions of the sulfoxide causes the non-equivalent ferrocenes in the truncated system to have different oxidation potentials. Synthesis was developed towards the synthesis of 1,8-bisferrocenyl-9-(alkylthio) anthracene complexes. It was observed that due to steric congestion at the C9 position of the anthracene scaffold, standard thionation reactions did not proceed as expected. Instead, the reaction of 1,8-dibromo-9-anthrone with Lawesson reagent afforded the intramolecular nucleophilic aromatic substitution cyclization product in quantitative yields. The reaction of the same anthrone under studied dithioketal formation conditions led to sulfur-rearrangement, giving the undesired 1,8-bisferrocenyl-10-(ethylthio)anthracene derivative, as confirmed by X-ray crystallography. Attempted Newman-Kwart rearrangement of 1, 8-dibromoanthracen-9-yl) dimethylcarbamothioate afforded no significant observed product formation, and decomposition of starting materials when heated for extended times. 1,8-bisferrocenyl-9-(methoxy)anthracene was synthesized and structurally characterized by dynamic X-ray crystallography to confirm connectivity. Electrochemical experiments show 2 reversible redox processes separated by 115 mV. Chemical oxidation experiments show unexpected, strong electronic coupling in the mixed valence complex. This coupling was characterized by near-IR absorption at 941 nm, indicating intervalence charge transfer (IVCT). Single electron reduction of 1,8-bisferrocenyl-9-(methoxy)anthracene, followed by quenching with various electrophiles afforded an inseparable mixture of products, one of which was identified by mass spectrometry as the desired 1,8-bisferrocenyl-9-(methylthio)anthracene product. However, this complex was not separable from the mixture and further characterization was not possible. All other routes attempted to incorporate sulfur into the system afforded no conversion of starting materials or decomposition of the reaction mixture.

I propose two new theories to explain the consumption of aversive experiences: valence conversion and the hedonic equation. The principle of valence conversion asserts that discrete emotions that share a similar set of cognitive appraisals and level of arousal, but are of opposite valence, can be quickly converted from one to the other contingent on internal cognitions, goals and cues from the environment. I propose that fear and excitement meet these conditions; thus, an aversive stimulus that is not too extreme as to prevent the activation of goals related to positive affect can also be interpreted as exciting. The hedonic equation postulates that across four time points (anticipatorily, in the moment, residually, and remembered), if the sum of excitement is greater than the sum of fear, an individual will choose to re-consume an aversive stimuli while controlling for other non-emotive motivations. These two theories together explain why some individuals willingly consume aversive experiences, even if at some points they are unpleasant.
2019-07-28

Mise en evidence et etude de deux grandes familles de composes dans le systeme la::(2)o::(3)-ao-cuo(a=ca,ba,sr) : la::(2-x)ba::(1-x)cu::(1-x/2)o::(5-x)(ln=la,nd) ou cu est essentiellement au degre d'oxydation 2 et une seconde famille caracterisee par la valence mixte du cuivre, les quantites de cuivre 3 pouvant atteindre dans certains cas 40%. Tous ces oxydes ont en commum leur appartenance a la structure perovskite. Proprietes electriques et magnetiques

Le sujet de la thèse concerne l’étude de l’inversion de valence dans des complexes FeIIFeIII induite par la déprotonation d’un ligand de FeII. L’intérêt de cette étude vient de ce que le processus considéré peut être décrit comme un transfert d’électron induit par un transfert de proton. Les transferts de protons et d’électrons sont au cœur de nombreuses réactions catalytiques ou biologiques et la compréhension des mécanismes de leur mise œuvre, séquentielle ou couplée, est un enjeu très actuel. La première partie de la thèse est consacrée à la caractérisation du premier système présentant cette propriété originale. Il est fondé sur un complexe binucléaire FeIIFeIII dont les deux ions Fe sont pontés par un dicarboxylate et un phénolate. Le FeIII est lié par un groupe bis-2-picolylamine et le FeII par un groupe similaire dans lequel une pyridine a été remplacée par une aniline. C’est la déprotonation de ce groupe aniline lié au FeII qui provoque l’inversion de valence, l’anilinate formé étant lié au FeIII. Le complexe aniline est isolé avec le groupe aniline en position -trans par rapport au phénolate pontant mais il possède la particularité de ne pas être stable en solution et de s’isomériser, le groupe aniline passant en position -cis par échange avec une pyridine. Le même phénomène est observé pour le complexe anilinate formé par déprotonation. Ce phénomène a été étudié en combinant les spectroscopies UV-visible, RMN du proton et Mössbauer et les caractéristiques thermodynamiques et cinétiques de l’isomérisation ont été déterminées. La relation entre le transfert d’électron et le transfert de proton a été étudiée par des techniques électrochimiques. Des études approfondies par cyclovoltamétrie et marquage isotopique ont montré que dans ce système les transferts d’électron et de proton sont concertés. La deuxième partie de la thèse est consacrée à l’étude des facteurs qui sont susceptibles d’influencer le transfert d’électron, c’est-à-dire les potentiels rédox des deux sites à Fe, et le transfert de proton, c’est-à-dire le pKa du ligand protique. Pour ce faire, de nouveaux complexes ont été préparés en modifiant soit le ligand protique, l’aniline étant remplacée par un benzimidazole, soit le groupe complexant le Fe, remplacement de la bis-2-picolylamine par la bis-(2-méthyl-N-méthylbenzimidazole)amine. Des complexes présentant ces modifications mais dépourvus du ligand acide ont été synthétisés pour étudier les effets de ces modifications sur les propriétés rédox des ions Fe. L’étude de l’influence des propriétés rédox a été menée dans un premier temps. La substitution du groupe complexant le FeIII n’a pas de conséquence importante au plan structural pour le complexe protoné qui existe toujours sous la forme de deux isomères. Par contre, après déprotonation un seul isomère existe. Les propriétés spectroscopiques sont peu altérées ce qui montre que la structure électronique du système n’est pas bouleversée. L’étude de l’influence des propriétés acides a été menée ensuite. Deux complexes ont été étudiés qui diffèrent par la nature du groupe complexant le FeIII. La substitution de l’aniline par le benzimidazole ne change pas de façon notable les propriétés structurales du système mais on note cependant que les valences des deux ions sont moins localisées. La déprotonation du benzimidazole est observée et conduit à un chromophore sensiblement différent du précédent illustrant les différences de ligand. L’étude électrochimique préliminaire révèle un comportement similaire au premier complexe étudié
The thesis matter concerns the valence inversion in FeIIFeIII induced by deprotonation of a FeII ligand. This study is of strong interest owing to the fact this process can be described as an electron transfer induced by a proton transfer. Protons and electrons transfers play essential roles in numerous catalytic or biologic reactions and therefore understanding whether they occur in a sequential or concerted manner is presently a major endeavor. The first part of the thesis is devoted to the characterization of the first system possessing this original property. It is based on binuclear complex FeIIFeIII where the two Fe ions are bridged by a dicarboxylate and a phenoxide. The ferric ion is bound by a bis-2-picolylamine group and the ferrous ion by a similar group where a pyridine has been replaced by aniline. Deprotonation of this FeII bound aniline induces the valence inversion, the resulting anilide being bound to the FeIII ion. The aniline complex was isolated with the aniline in trans position with respect to the bridging phenoxide, but it is not stable in solution and isomerizes, the aniline group moving to a cis position upon exchange with a pyridine. The same phenomenon was observed for the anilide complex obtained through deprotonation. This phenomenon was studied by combining UV-visible, 1H-RMN and Mössbauer spectroscopies, and the thermodynamic and kinetic characteristics of the isomerization were determined. The link between the electron transfer and the proton transfer were studied by electrochemical techniques. Thorough studies by cyclic voltammetry and isotopic labeling showed that in this system the electron and proton transfers are concerted. The second section of the thesis was aimed at studying the factors susceptible to influence the electron transfer, namely the redox potentials of the two Fe sites, and the proton transfer, namely the pKa of the protic ligand. To achieve it, new complexes were prepared by modifying either the protic ligand, the aniline being replaced by a benzimidazole, or the Fe binding group, substitution of bis-2-picolylamine by bis-(2-methyl-N-methylbenzimidazole)amine. Model complexes incorporating these changes but deprived of the protic ligand were also obtained to assess their influence on the redox properties of the Fe ions. The study of the influence of redox properties was considered first. The substitution of the group complexing FeIII has not a strong influence on the structure of the protonated complex which still exists as two isomers. By contrast, after deprotonation a single isomer exists. The spectroscopic properties are mostly unchanged which shows that the electronic structure of the system is not altered significantly. The study of the influence of the acidicity was then conducted. Two complexes differing by the nature of the FeIII bound group were considered. Replacing aniline by benzimidazole does not change significantly the structural properties of the system, but the valences of the Fe ions are less localized than in the original complex. The deprotonation of benzimidazole occurs and leads to a chromophore that differs from the preceding, revealing the difference in ligands. However, a preliminary electrochemical study reveals a behavior similar to that of the original complex

Ce travail porte sur la synthèse et la caractérisation d’oxydes de manganèse de formule généraleCaxMnyOz avec y/x > 1. Par une approche de chimie du solide, les propriétés redox de ces matériauxseront corrélées à leur composition chimique et leur structure cristalline ce qui constitue une étude enamont de l’application pour ces systèmes pouvant jouer le rôle de tampon à oxygène dans desprocessus catalytiques. Les composés ont été synthétisés par autocombustion en voie aqueuse etcaractérisés d’un point de vue structural. Les propriétés redox ont été évaluées par ATG et lespropriétés de réductibilité par H2-TPR pour certains composés. Quelles que soient la structure, ladimensionnalité ou la valence du manganèse dans les composés oxydés (Mn4+/Mn3+), le manganèsese réduit totalement en Mn2+ sous atmosphère réductrice (Ar/H2). Les composés réduits cristallisentdans une solution solide de type NaCl de formule Ca1-xMnxO. Les mécanismes de réduction dumanganèse au sein de ces structures ont été appréhendés sur la base des analysesthermogravimétriques. Afin de faire varier les températures de réduction, l’iono-covalence de la liaisonMn-O a été modifiée via des substitutions cationiques (i) sur les sites du calcium principalement ausein de réseaux 2D ou (ii) sur les sites du manganèse essentiellement dans les réseaux 3D avec laprésence d’Al3+ ou de Fe3+ de rayons ioniques comparables respectivement à Mn4+ et Mn3+. Lessolutions solides ont été caractérisées d’un point de vue structural mais aussi pour leurs propriétésredox. Il convient de souligner que les phases substituées au Fer présentent des propriétés redox toutà fait remarquables dans la mesure où les ions Fe3+ tout comme Mn4+/3+ se réduisent d’abord en Fe2+puis en Fe° qui est dès lors expulsé hors de la matrice oxyde. Lors de la réoxydation, le fer réintègrele réseau 3D et les matériaux sont cyclables dans des conditions réductrices puis oxydantes à l’air àdes températures inférieures à 1000°C
This work deals with the synthesis and characterization of manganese oxides with CaxMnyOz formulaand y/x >1. According to a solid state chemistry scope, the redox properties of these materials will becorrelated to their chemical composition and crystallographic structure which constitutes a forehandexploratory study of compounds that are intended to be used for the automotive catalysis exhaustbased on the three-way catalysis principle. The materials were synthesized by aqueous selfcombustionroute and structurally characterized. Redox properties and reducibility properties wereevaluated by TGA and H2-TPR, respectively. Whatever the structure, the dimensionality of the networkor the manganese valence in the starting oxidized material, all of the manganese ions are completelyreduced (Mn2+) in a Ar/H2 atmosphere. The reduced compounds crystallize in a rock-salt type solidsolution with the formula Ca1-xMnxO. The mechanisms of manganese reduction within these structureswere explored on the basis of TGA analysis. In order to tune the reduction temperatures, the ionocovalenceof the Mn-O bond has been modified by either cationic substitution of calcium in the 2Dnetworks or either substitution of manganese in the 3D networks. In this last case, Substituting ionswere Al3+ and Fe3+ which ionic radii comparable to Mn4+ and Mn3+, respectively. Solid solutions havebeen characterized from a structural point of view but also for their redox properties. One shouldnotice that iron substituted compounds exhibit remarkable redox properties because Fe3+ ions firstreduce in Fe2+ iron before a final reduction in Fe° that is consequently expulsed from the matrix. Atreoxidation, iron returns into the 3D network and cycling can be observed when reducing and oxidizingat temperatures lower than 1000°C

CoordenaÃÃo de AperfeiÃoamento de NÃvel Superior
Os compostos trans-[Co(cyclam)(SO3)(NCS)]Â4H2O, trans-[Ru(NH3)4(NCS)(SO4)] e trans-[(SO3)(cyclam)Co−NCS−Ru(NH3)4(NCS)](BF4), onde cyclam = 1,4,8,11-tetraazaciclotetradecano, foram sintetizados e caracterizados por difraÃÃes de raios-X, espectroscopias vibracional na regiÃo do infravermelho e eletrÃnica nas regiÃes do ultravioleta e visÃvel (UV-Vis) e por tÃcnicas eletroquÃmicas. O grau de comunicaÃÃo eletrÃnica entre os Ãtomos de Co e Ru do complexo binuclear foi avaliado por eletroquÃmica e espectroscopia eletrÃnica na regiÃo do infravermelho prÃximo. Apenas para o complexo trans-[Co(cyclam)(SO3)(NCS)]Â4H2O foi possÃvel a obtenÃÃo de cristais que permitiram a determinaÃÃo estrutural. Os dados obtidos indicam estrutura monoclÃnica com o ligante cyclam no plano equatorial e os ligantes SO32− e NCS− ocupando posiÃÃes trans e coordenados ao Ãtomo de Co atravÃs, respectivamente, dos Ãtomos de S e N. Este resultado à reforÃado atravÃs da observaÃÃo, no espectro vibracional, de bandas tipicamente atribuÃdas ao ligante cyclam quando este se encontra em uma geometria trans. Os resultados de voltametria cÃclica deste composto indicam um mecanismo eletroquÃmico-quÃmico-eletroquÃmico. De fato, os experimentos de espectroeletroquÃmica (potencial controlado em -0,80 V vs Ag/AgCl) indicam que este composto experimenta, apÃs reduÃÃo, reaÃÃo de substituiÃÃo das molÃculas SO32− e NCS− por molÃculas do solvente (L), formando compostos do tipo [Co(cyclam)(L)2]2+. A observaÃÃo, no espectro vibracional do complexo trans-[Ru(NH3)4(NCS)(SO4)], das bandas em 2132, 887 e 478 cm-1, atribuÃdas aos modos de νCN, νCS e δ(NCS), respectivamente, do ligante NCS−, indica a coordenaÃÃo deste grupo atravÃs do Ãtomo de nitrogÃnio. Estudos eletroquÃmicos e de espectroscopia eletrÃnica deste composto em meio aquoso indicam que a reduÃÃo do centro metÃlico induz a reaÃÃo de substituiÃÃo do ligante SO42− por uma molÃcula de H2O. A reaÃÃo para formaÃÃo do composto binuclear, portanto, foi realizada em condiÃÃes redutoras a fim de induzir a formaÃÃo do aquo-complexo de rutÃnio e, em seguida, a reaÃÃo de substituiÃÃo da molÃcula de H2O por um sÃtio de coordenaÃÃo do monÃmero trans- [Co(cyclam)(SO3)(NCS)]Â4H2O. Os resultados obtidos para o material isolado indicam que hà a formaÃÃo do complexo binuclear com o ligante NCS− ocupando a posiÃÃo ponte. A curva voltamÃtrica obtida para este composto apresenta dois pares de ondas redox com potenciais formais de meia-onda (E1/2) em −0,27 e 0,13 V vs Ag|AgCl atribuÃdos, respectivamente, aos centros metÃlicos de Co e Ru. Comparativamente aos monÃmeros, hà a observaÃÃo de um deslocamento positivo de potencial o que reflete a estabilizaÃÃo do estado reduzido para o Ãtomo de rutÃnio, RuII, e desestabilizaÃÃo do estado oxidado para o Ãtomo de cobalto, CoIII. Este resultado à atribuÃdo a coordenaÃÃo a um centro oxidado, CoIII, cuja carga nuclear efetiva aumenta a deslocalizaÃÃo de densidade eletrÃnica aumentando o carÃter retirador do ligante ponte NCS−. O valor da constante de comproporcionamento, Kc = 5,78 x 106, calculada a partir da diferenÃa entre os valores de E1/2, indica um forte grau de comunicaÃÃo entre os centros metÃlicos e classifica este complexo como um sistema de valÃncia mista de classe II.
Trans-[Co(cyclam)(SO3)(NCS)]Â4H2O, trans-[Ru(NH3)4(NCS)(SO4)], and trans-[(SO3)(cyclam)Co−NCS−Ru(NH3)4(NCS)](BF4) complexes, where cyclam = 1,4,8,11-tetraazacyclotetradecane, were synthesized and characterized by X-ray difraction, vibrational and electronic (ultraviolet, visible and near infrared) spectroscopies, and electrochemical techniques. The electronic communication between Co and Ru metal centers of the binuclear complex was evaluated by electrochemistry and electronic spectrocopy in the near infrared region. Crystals suitable for X-ray studies were only isolated for the trans-[Co(cyclam)(SO3)(NCS)]Â4H2O complex. The obtained results indicate a monoclic structure with cyclam ligand at the equatorial plane and SO32− and NCS− moieties occupying the axial positions being coordinated through, respectively, sulfur and nitrogen atoms. This result is reinforced by the observation, in the vibrational spectrum, of bands typically assigned to the cyclam ligand in a trans configuration. The cyclic voltammograms obtained for this compound indicate as Electrochemical-Chemical-Electrochemical mechanism. In fact, the spectroelectrochemical experiments obtained at -0.80 V vs Ag/AgCl show that this compound, upon reduction, suffers a substitution reaction in which the SO32− and NCS− moieties are replaced by solvent molecules (L) thus forming [Co(cyclam)(L)2]2+ type complexes. The observation in the vibrational spectrum of the trans-[Ru(NH3)4(NCS)(SO4)] complex of the 2132, 887 e 478 cm-1 bands assigned, respectively, to the νCN, νCS e δ(NCS) vibrational modes of the NCS− ligand indicates that this moiety is coordinated through the nitrogen atom. Electrochemical and spectroscopic studies of this compound in aqueous medium indicate that the reduction of the metal center induces the replacement of SO42− ligand by a water molecule. The synthesis of the binuclear compound, therefore, was made under reductive conditions aiming to produce the aquo-complex and, then, replace the water molecule by a coordination site of the trans-[Co(cyclam)(SO3)(NCS)]Â4H2O complex. The results obtained for the isolated material hints that the binuclear complex is formed with the NCS− fragment as the bridge ligand. The acquired cyclic voltammogram presents two redox process with the half-wave formal potentials (E1/2) observed at −0.27 and 0.13 V vs Ag|AgCl and being assigned to the Co and Ru metal centers, respectively. In comparison to the monomers, the positive potential shift reflects the stabilization of the reduced state of the ruthenium metal atom (RuII) and the destabilization of the cobalt metal center (CoIII). This result is assigned to the coordination to an oxidated metal center, CoIII, whose effective nuclear charge increased the electronic delocalization increasing the withdrawing character of the NCS− bridge ligand. The comproportionation constant, Kc = 5.78 x 106, was calculated from the difference between the E1/2 values. The Kc value indicates a strong electronic communication between the metal atoms and classifies this binuclear complex as a mixed valence system of class II.

SILVA, M. A. S. Síntese e Caracterização do Composto Heterobimetálico trans-[(SO3)(cyclam)Co-NCS-Ru(NH3)4(NCS)](BF4). 2009. 101 f. Dissertação (Mestrado em Química) - Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2009.
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Trans-[Co(cyclam)(SO3)(NCS)]·4H2O, trans-[Ru(NH3)4(NCS)(SO4)], and trans-[(SO3)(cyclam)Co−NCS−Ru(NH3)4(NCS)](BF4) complexes, where cyclam = 1,4,8,11-tetraazacyclotetradecane, were synthesized and characterized by X-ray difraction, vibrational and electronic (ultraviolet, visible and near infrared) spectroscopies, and electrochemical techniques. The electronic communication between Co and Ru metal centers of the binuclear complex was evaluated by electrochemistry and electronic spectrocopy in the near infrared region. Crystals suitable for X-ray studies were only isolated for the trans-[Co(cyclam)(SO3)(NCS)]·4H2O complex. The obtained results indicate a monoclic structure with cyclam ligand at the equatorial plane and SO32− and NCS− moieties occupying the axial positions being coordinated through, respectively, sulfur and nitrogen atoms. This result is reinforced by the observation, in the vibrational spectrum, of bands typically assigned to the cyclam ligand in a trans configuration. The cyclic voltammograms obtained for this compound indicate as Electrochemical-Chemical-Electrochemical mechanism. In fact, the spectroelectrochemical experiments obtained at -0.80 V vs Ag/AgCl show that this compound, upon reduction, suffers a substitution reaction in which the SO32− and NCS− moieties are replaced by solvent molecules (L) thus forming [Co(cyclam)(L)2]2+ type complexes. The observation in the vibrational spectrum of the trans-[Ru(NH3)4(NCS)(SO4)] complex of the 2132, 887 e 478 cm-1 bands assigned, respectively, to the νCN, νCS e δ(NCS) vibrational modes of the NCS− ligand indicates that this moiety is coordinated through the nitrogen atom. Electrochemical and spectroscopic studies of this compound in aqueous medium indicate that the reduction of the metal center induces the replacement of SO42− ligand by a water molecule. The synthesis of the binuclear compound, therefore, was made under reductive conditions aiming to produce the aquo-complex and, then, replace the water molecule by a coordination site of the trans-[Co(cyclam)(SO3)(NCS)]·4H2O complex. The results obtained for the isolated material hints that the binuclear complex is formed with the NCS− fragment as the bridge ligand. The acquired cyclic voltammogram presents two redox process with the half-wave formal potentials (E1/2) observed at −0.27 and 0.13 V vs Ag|AgCl and being assigned to the Co and Ru metal centers, respectively. In comparison to the monomers, the positive potential shift reflects the stabilization of the reduced state of the ruthenium metal atom (RuII) and the destabilization of the cobalt metal center (CoIII). This result is assigned to the coordination to an oxidated metal center, CoIII, whose effective nuclear charge increased the electronic delocalization increasing the withdrawing character of the NCS− bridge ligand. The comproportionation constant, Kc = 5.78 x 106, was calculated from the difference between the E1/2 values. The Kc value indicates a strong electronic communication between the metal atoms and classifies this binuclear complex as a mixed valence system of class II.
Os compostos trans-[Co(cyclam)(SO3)(NCS)]·4H2O, trans-[Ru(NH3)4(NCS)(SO4)] e trans-[(SO3)(cyclam)Co−NCS−Ru(NH3)4(NCS)](BF4), onde cyclam = 1,4,8,11-tetraazaciclotetradecano, foram sintetizados e caracterizados por difrações de raios-X, espectroscopias vibracional na região do infravermelho e eletrônica nas regiões do ultravioleta e visível (UV-Vis) e por técnicas eletroquímicas. O grau de comunicação eletrônica entre os átomos de Co e Ru do complexo binuclear foi avaliado por eletroquímica e espectroscopia eletrônica na região do infravermelho próximo. Apenas para o complexo trans-[Co(cyclam)(SO3)(NCS)]·4H2O foi possível a obtenção de cristais que permitiram a determinação estrutural. Os dados obtidos indicam estrutura monoclínica com o ligante cyclam no plano equatorial e os ligantes SO32− e NCS− ocupando posições trans e coordenados ao átomo de Co através, respectivamente, dos átomos de S e N. Este resultado é reforçado através da observação, no espectro vibracional, de bandas tipicamente atribuídas ao ligante cyclam quando este se encontra em uma geometria trans. Os resultados de voltametria cíclica deste composto indicam um mecanismo eletroquímico-químico-eletroquímico. De fato, os experimentos de espectroeletroquímica (potencial controlado em -0,80 V vs Ag/AgCl) indicam que este composto experimenta, após redução, reação de substituição das moléculas SO32− e NCS− por moléculas do solvente (L), formando compostos do tipo [Co(cyclam)(L)2]2+. A observação, no espectro vibracional do complexo trans-[Ru(NH3)4(NCS)(SO4)], das bandas em 2132, 887 e 478 cm-1, atribuídas aos modos de νCN, νCS e δ(NCS), respectivamente, do ligante NCS−, indica a coordenação deste grupo através do átomo de nitrogênio. Estudos eletroquímicos e de espectroscopia eletrônica deste composto em meio aquoso indicam que a redução do centro metálico induz a reação de substituição do ligante SO42− por uma molécula de H2O. A reação para formação do composto binuclear, portanto, foi realizada em condições redutoras a fim de induzir a formação do aquo-complexo de rutênio e, em seguida, a reação de substituição da molécula de H2O por um sítio de coordenação do monômero trans- [Co(cyclam)(SO3)(NCS)]·4H2O. Os resultados obtidos para o material isolado indicam que há a formação do complexo binuclear com o ligante NCS− ocupando a posição ponte. A curva voltamétrica obtida para este composto apresenta dois pares de ondas redox com potenciais formais de meia-onda (E1/2) em −0,27 e 0,13 V vs Ag|AgCl atribuídos, respectivamente, aos centros metálicos de Co e Ru. Comparativamente aos monômeros, há a observação de um deslocamento positivo de potencial o que reflete a estabilização do estado reduzido para o átomo de rutênio, RuII, e desestabilização do estado oxidado para o átomo de cobalto, CoIII. Este resultado é atribuído a coordenação a um centro oxidado, CoIII, cuja carga nuclear efetiva aumenta a deslocalização de densidade eletrônica aumentando o caráter retirador do ligante ponte NCS−. O valor da constante de comproporcionamento, Kc = 5,78 x 106, calculada a partir da diferença entre os valores de E1/2, indica um forte grau de comunicação entre os centros metálicos e classifica este complexo como um sistema de valência mista de classe II.

L'études des combinaisons ternaires soufrées formées par l'europium et un second métal conduit dans de nombreux cas a des composes qui ne contiennent que de l'europium divalent, tels que Eu3Sb4S9, EuLn2S4 (Ln: Dy—Lu, Y) et Eu1,1Bi2S4. . Dans ces trois composes Eu (ii) présente un environnement 8-prismatique et le second métal, un environnement octaédrique. Dans Eu3Sb4S9, le doublet 5s2 non-engagé de Sb (iii) crée de larges tunnels au sein de la structure. Les composés EuLn2S4 ont une structure de type CaFe2O4. Le réseau du composé Eu1, 1Bi2S4 contient de larges canaux partiellement occupés par des atomes d'europium divalent d'environnement 9-prismatique. Dans quelques cas, lorsque le second métal est susceptible de stabiliser partiellement la valence iii de l'europium, des composés à valence mixte sont obtenus, tels Eu2BiS4 et Eu2CuS3 qui contiennent les deux valences de l'europium, mais de façon différenciée par des sites cristallographiques distincts. Dans Eu2BiS4, Eu(ii) a un environnement 7-prismatique, Eu (iii), 7-octaedrique et Bi (iii), octaédrique. Dans Eu2CuS3, Eu (ii) a un environnement 8-prismatique, Eu(iii), octaédrique et Cu (i),tétraédrique. Dans ces deux composés, il existe des feuillets perpendiculaires à l'axe b, de formule Eurs(3) (r = Cu ou Bi). Tous ces composés sont paramagnétiques et semi-conducteurs. Cette étude met en évidence la stabilité de l'état divalent de l'europium dans les sulfures et la nécessité pour obtenir des composes à valeur mixte ou intermédiaire de l'europium, de modifier les conditions d'études, telles que la température et la pression.

本文データは平成22年度国立国会図書館の学位論文(博士)のデジタル化実施により作成された画像ファイルを基にpdf変換したものである
Kyoto University (京都大学)
0048
新制・課程博士
博士(理学)
甲第4980号
理博第1377号
新制||理||769(附属図書館)
UT51-92-J27
京都大学大学院理学研究科化学専攻
(主査)教授 齋藤 軍治, 教授 小菅 皓二, 教授 新庄 輝也
学位規則第4条第1項該当

The field of organic electronics, in which -conjugated, organic molecules and polymers are used as the active components (e.g., semiconductor, light emitter/harvester, etc.), has lead to a number a number of key technological developments that have been founded within fundamental research disciplines. In the Dissertation that follows, the research involves the use of quantum-chemical techniques to elucidate fundamental aspects of both intermolecular and intramolecular electron-transfer processes in organic, -conjugated molecules. The Dissertation begins with an introduction and brief review of organic molecular systems used as electron-transport semiconducting materials in device applications and/or in the fundamental studies of intramolecular mixed-valence processes. This introductory material is then followed by a brief review of the electronic-structure methods (e.g., Hartree-Fock theory and Density Functional Theory) and electron-transfer theory (i.e., semiclassical Marcus theory) employed throughout the investigations. The next three Chapters deal with investigations related to the characterization of non-rigid, -conjugated molecular systems that have amorphous solid-state properties used as the electron-transport layer in organic electronic and optoelectronic devices. Chapters 3 and 4 involve studies of silole- (silacyclopentadiene)-based materials that possess attractive electronic and optical properties in the solid state. Chapter 5 offers a preliminary study of dioxaborine-based molecular structures as electron-transport systems. In Chapters 6 8, the focus of the work shifts to investigations of organic mixed-valence systems. Chapter 6 centers on the examination of tetraanisylarylenediamine systems where the inter-redox site distances are approximately equal throughout the series. Chapter 7 examines the bridge-length dependence of the geometric structure, charge-(de)localization, and electronic coupling for a series of vinylene- and phenylene-vinylene-bridged bis-dianisylamines. In Chapter 8, the role of symmetric vibrations in the delocalization of the excess charge is studied in a dioxaborine radical-anion and a series of radical-cation bridged-bisdimethylamines. Finally, Chapter 9 provides a synopsis of the work and goals for future consideration.

A large variety of diferrocenyl compounds bridged by an organic wire fragment in a generic form of -CH=CH-X-CH=CH- were first synthesized, in which the X unit is a functional group/atom. These compounds were studied by structural analysis, electrochemistry, intervalence NIR absorption and other spectroscopic techniques. The results indicated that metal-ligand redox matching is most essential in facilitating long-range electron transfer in the mixed-valence complexes. A series of doubly-bridged diferrocenyl compounds and wire-linked triferrocenes were also synthesized and studied. All doubly-bridged diferrocenyl compounds demonstrated nearly doubled electronic coupling in comparison to their singly-bridged analogues. Thus the use of parallel wires in such systems represents a facile approach to improve communication in molecular electronics. For triferrocenes linked by symmetric wires, the electronic interaction between the redox-active centers was rather dynamic when the bridging component was short or the charge was delocalized among the ligand and metal centers. For triferrocenes bridged by asymmetric wires, depending on the direction of the polar linking chain, the central ferrocene becomes a molecular switch, turning on or off the communication between the two end ferrocenes. Finally, to eliminate the metal-ligand orbital mixing problem, we also bound the wires with two redox-active styrylpyrrole termini, for which the molecules are purely organic. It was found that when the ð-conjugation was maintained, the oligomers were fully delocalized systems.

The local structures of the iron atoms for a series of strongly coupled Fe 2 (TIED)L 4 complexes (TIED = tetraiminethylenedimacrocycle, L = axail ligand) have been investigated by K-edge X-ray Absorption Spectroscopy (XAS). These complexes include not only the well characterized iso-valence CH 3 CN complex, mixed-valence CH 3 CN and Cl − complexes, and previously reported iso-valence CO complex but also the new isolated solids of iso-valence Fe 2 TIED complexes with Cl − , Br − , imidazole, pyridine, histidine, N,N-dimethyformamide (DMF), SCN − , and CN − as axial ligands and mixed-valence complexes with Br − and imidazole as axial ligands. The average Fe-N distances for the first coordination sphere of the iron atom obtained by EXAFS analysis are 1.94, 1.94, 1.95, 1.96, 1.94, 1.93, 1.96, 1.96, 1.96, and 1.96 Å for the iso- and mixed-valence CH 3 CN and imidazole complexes and iso-valence complexes with SCN − , CN − , CO, pyridine, histidine, and DMF as axial ligands, respectively. Two-shell fitting analyses of the complexes gave average iron to the four planar coordinated nitrogen distance of 1.90, 1.91, 1.91, 1.92, and 1.92 Å for the Fe 2 (TIED)L 4 with L = DMF, pyridine, Cl − , Br − , imidazole, and histidine complexes, respectively. The average distances from the center iron to: N(DMF), 2.05; N(pyridine), 2.05; Cl − , 2.33; Br − , 2.45; N(imidazole), 2.08; and N(histidine), 2.07 Å. They are all comparable to related bond distances in the literature. The above data indicate that there is no significant difference in the average Fe-N distances between each of the iso- and mixed-valence pairs. Also different axial ligands do not cause significant impact on the average Fe-N distances from the iron atom to the four coordinated N in the TIED ligand. The threshold edge positions shift about +1 eV from the iso-valence CH 3 CN, Cl − , and Br − complexes to their corresponding mixed-valence complexes. The relatively small shift compared with the normal +2 [special characters omitted] +3 eV edge shift from Fe 2+ to Fe 3+ reflects the oxidation state change of iron from Fe 2+ to Fe 2.5+ . The edge energy of the isovalence diiron complexes with different axial ligands increases in the order of the spectrochemical series of the axial Iigands from strong to weak field Iigands as follows [58, 59]: [special characters omitted] All the complexes studied here have a weak dipole-forbidden 1s → 3d pre-edge transition. The low intensity indicates only a small distortion of the octahedral coordination geometry of the central iron atom.

The study of macrocyclic ligands for complexation of alkali metals (macrobicyclic polyether cryptands) and transition metals (tetraaza macrocycles) is reported. The synthesis of a new bis(phosphotriester) macrobicyclic polyether cryptand, O = P (O(CH$\sb2)\sb2\rm O(CH\sb2)\sb2O(CH\sb2)\sb2O\rbrack\sb3$ P = O, 1, called phosphocrypt, and its acyclic tripodal precursor O = P (O(CH$\sb2)\sb2\rm O(CH\sb2)\sb2O(CH\sb2)\sb2OH\rbrack\sb3$, 2, is described. Aqueous stability constants (K$\sb{\rm s}$) measured with a cation selective electrode with potassium and rubidium are 10$\sp{3.7}$ and 10$\sp{3.6}$ for 1, and are 10$\sp{3.6}$ and 10$\sp{3.0}$ for 2, respectively. The K$\sb{\rm s}$ values for phosphocrypt are 1000 fold greater than comparably sized nitrogen bridgehead cryptands. $\sp1$H and $\sp{13}$C NMR indicate 1 is flexible at 20$\sp\circ$C. Molecular mechanics calculations confirm the flexibility of 1. Also reported are the synthesis and characterization of (1) a new mixed-valence bimetallic ruthenium complex, Ru$\sb2\rm (C\sb{20}H\sb{36}N\sb8)Cl\sb{4}\sp{+}$, 3, that contains a cross-conjugated bridge that links two tetraaza macrocycles; and (2) the formation, physical properties, and reduction chemistry of a new iron $\beta$-diimine keto macrocyclic complex, Fe(C$\rm \sb{10}H\sb{18}N\sb{4}O)(CH\sb3CN)\sb{2}\sp{2+},$ 4. The ruthenium dimer 3 was formed by oxidative dehydrogenation of Ru(C$\rm\sb{10}H\sb{24}N\sb4)(Cl\sb2)\sp+$ and its mass was determined by positive ion fast atom bombardment mass spectrometry. The binuclear species 3 is assigned as a Robin and Day strongly coupled class III mixed-valence species based on cyclic voltammetry, electronic spectroscopy, and X-ray photoelectron spectroscopy (XPS). The XPS photopeaks of 3 for the binding energies from the Ru 3p$\sb{1/2}$ and Ru 3p$\sb{3/2}$ regions show only a single peak, indicating the unpaired electron is delocalized on the short (10$\sp{-17}$ s) timescale of the XPS experiment. The keto complex 4 was formed in high yields ($>$90%) from the reaction of Fe$\rm\sb2(C\sb{20}H\sb{36}N\sb8)(CH\sb3CN)\sb{4}\sp{4+}$, 5, (the diiron analog of 3) with molecular oxygen. Its mass was determined by electrospray mass spectrometry and its structure by NMR spectroscopy ($\sp1$H, $\sp{13}$C, COSY, NOE DIFF). The complex is rigid at room temperature in CD$\sb3$CN and this allows the assignment of the ten distinct protons. Reduction of the keto group in 4 under anaerobic conditions, followed by aerobic oxidation, leads to the reformation of 5.

Les adduits cuivre-oxygène dans les métallo-enzymes ont été proposés comme étant responsables de l'activation de liaisons C-H, processus qui ont un intérêt pour des applications industrielles potentielles. La première partie de ce travail est consacrée à une présentation de différentes mono-oxygénases à cuivre et de leurs complexes modèles. Récemment, des intermédiaires réactionnels ont émergé et parmi ceux-ci, des espèces de valence mixte CuIICuIII ont été proposées comme étant des espèces réactives clés pour l'activation de liaisons C-H fortes.Dans ce travail, à partir de ligands binucléants basés sur un espaceur 1,8-naphtyridine, la stabilisation et les caractérisations spectroscopiques de ce type d’intermédiaires à haut degré d’oxydation sont explorées. La préparation d’espèces Cu2:O2 à partir de l'activation du dioxygène par les complexes CuI2 est discutée. Deux complexes µ-ɳ2:ɳ2-peroxo-CuII2 ont été préparés à -80°C et caractérisés par différentes méthodes spectroscopiques associées à des calculs par la théorie de la fonctionnelle de la densité (DFT). A partir de nouveaux ligands dissymétriques possédant une fonction amide, nos tentatives pour contrôler la préparation des complexes binucléaires associés sont également présentées. Puis, les caractérisations des espèces à valence mixte CuIICuIII obtenues par mono-oxydation électronique des complexes CuII2 sont décrites (voltammétrie cyclique, résonance paramagnétique électronique, UV-visible, proche infrarouge et DFT).Enfin, ce travail est complété par l’étude de la réactivité des espèces CuIICuIII, pour lesquelles la littérature est presque inexistante. Lorsque des ligands stériquement encombrés sont utilisés dans les espèces à valence mixte, des oxydations intramoléculaires sont observées, alors que l’espèce CuIICuIII possédant un ligand moins encombré oxyde le toluène. Il est à noter que l'ajout d'une base rend le système catalytique
Copper-oxygen adducts in enzymes have been proposed to be responsible for the activation of C-H bonds, a process that has industrial applications. The first part of this thesis is therefore dedicated to a discussion on various copper oxygenases and their model complexes. Recently, key reactive intermediates have emerged and among them mixed valent CuIICuIII species have been proposed to be responsible for strong C-H bond activation.In this work the stabilisation and spectroscopic characterisation of high valent intermediates using dinucleating ligands based on a 1,8-naphthyridine spacer are explored. The generation of Cu2:O2 species from the activation of O2 by CuI2 complexes is discussed. Two µ-ɳ2:ɳ2-peroxo-CuII2 complexes have been prepared at -80°C and characterised by spectroscopy and density functional theory (DFT). Our attempts at generating dinuclear systems using new dissymmetric ligands with an amide function are also discussed. Finally the successful characterisation of mixed valent CuIICuIII species by mono-electronic oxidation of CuII2 complexes is described (cyclic voltammetry, electron paramagnetic resonance, UV-visible, near infrared and DFT).The last part focusses on probing the reactivity of CuIICuIII species, for which the literature is almost inexistent. When sterically congested ligands are used to support the mixed valent system, intramolecular aliphatic C-H oxidation was observed, whether as the CuIICuIII species supported by a less bulky ligand was able to oxidise toluene. Interestingly the addition of a base made the system catalytic

Les travaux présentés dans cette thèse s’inscrivent dans une thématique de modification de surfaces par le biais de monocouches auto-assemblées post-fonctionnalisables. L’objectif principal consiste à élaborer une méthode générique de modification de monocouches par des motifs moléculaires variés. Pour cela, les travaux se concentrent sur la mise au point d’une plateforme générique facilement fonctionnalisable par un motif d’intérêt et greffable sur électrode modifiée. La voie retenue consiste à utiliser deux réactions de "click chemistry" de type "CuAAC". La première réaction de CuAAC s’effectue en solution et permet de solidariser plateforme et motifs d’intérêt (principalement des dérivés ferrocényles). Les ligands ainsi obtenus ont été utilisés pour la complexation d’ions métalliques (Cu2+, Zn2+). Les ligands et les complexes ont été étudiés en solution par électrochimie ainsi que par spectroscopies UV-Visibles et RPE. La seconde réaction de CuAAC permet l’immobilisation des différents complexes de cuivre sur des électrodes pré-modifiées par des fonctions azoture, généralement à l’aide de monocouches auto-assemblées. Ce greffage s’effectue selon le mode opératoire de l’"électroclick auto-induite", c'est-à-dire que le complexe de cuivre à immobiliser est également catalyseur de la réaction de CuAAC. Les systèmes ainsi immobilisés (mono-, bi- ou tri-métalliques) ont pu être étudiés en terme de cinétique d’immobilisation, de cinétique de transfert d’électrons et en réactivité. Ce dernier point a par ailleurs fait l’objet d’une attention particulière pour le cas de la réduction électro-catalytique des ions nitrite par les complexes de cuivre (I), en solution et sur surface
This work depends on functionalized surface theme using modification of selfassembled monolayers (SAMs). The main objective consists to elaborate a new general pathway to modify monolayers with miscellaneous objects of interest. For this, we decide to focus our work to synthesize a versatile platform handling two ethynyl arms. These functions are available to operate two CuAAC reactions. The first one is use for linking platform with object of interest (in general ferrocenyl derivatives). Ligands obtained by that way were used for complexation of Cu2+ and Zn2+ ions. Electrochemical and spectroscopic (UV-Visible and EPR) studies were performed on these compounds. The second CuAAC reaction is used to immobilize copper complexes on azide modified electrode (azide derivatives SAMs on gold and ITO or direct functionnalization of glassy carbon surface). The grafting is operating through “self-induced electroclick” method; this means the CuAAC reaction is catalysed by the copper complex which is immobilized. Functionalized electrodes were characterized by cyclic voltammetry. It appears that similar complexes have closed grafting kinetic. These studies also demonstrate the both influence of copper and spacer on a second electroactive site (ferrocene moieties). The reactivity of copper centre is evaluated for complexes in solution and immobilized on surface with electrocatalytic reduction of nitrite ions by copper (I) species. The catalytic efficiency strongly depends on potential of copper reduction. Also, similar complexes show a loss of catalytic power with immobilization on surface

La dimensione annuale della Global DataSphere (quantità totale di dati creati nel mondo) è aumentata esponenzialmente nell'ultimo decennio e supererà i 150 trilioni di gigabyte entro il 2025. L'archiviazione e l'elaborazione dei dati sono tra i target primari in campi emergenti come le tecnologie quantistiche e la spintronica (spin elettronica). Un importante obiettivo è il controllo delle proprietà magnetiche e dello spin a livello atomico e molecolare. Interessanti, sono nanostrutture chiamate Magneti a Molecola Singola (SMM), che possiedono proprietà magnetiche simili a quelle dei magneti tradizionali, ma con origine puramente molecolare. La bistabilità magnetica e i lunghi tempi di rilassamento possono rendere i SMM applicabili come singoli bit. Le loro proprietà fisiche possono essere ottimizzate mediante design chimico. Gli EMAC (Extended Metal Atom Chains) a base di ferro(II) sono potenziali SMM, per via del grande spin e anisotropia magnetica del Fe2+ ad alto spin. Gli EMAC sono catene lineari di almeno tre ioni metallici, avvolti da leganti organici polidentati, che promuovono corte distanze tra i metalli e, a volte, legami metallo-metallo. Tuttavia, è difficilissimo isolare questi composti per via della grande tendenza di Fe2+ a subire processi di ossidazione e idrolisi. Infatti, prima che nel 2018 noi pubblicassimo una catena di 4 ioni Fe2+, [Fe4(tpda)3Cl2] (1), con leganti oligo--piridilamminici, l'unico EMAC noto a base di ferro(II) era un catena di 3 Fe (2, Cotton et al. nel 1998). Nel 2020, Guillet et al. ha riportato un nuovo complesso di 3 Fe2+ (3) con leganti sililati. I complessi 1, 2 e 3 mostrano interazioni ferromagnetiche, mentre 3 contiene anche legami metallo-metallo. L’obiettivo di questa Tesi è la progettazione, sintesi e caratterizzazione di composti di metalli di transizione con stati elettronici altamente magnetici, contenenti interazioni ferromagnetiche e, eventualmente, legami metallo-metallo. In particolare, essa descrive uno studio sistematico di una serie di EMAC a base di ferro, ottenuti e maneggiati in condizioni strettamente anaerobiche e anidre. I nuovi composti sono stati caratterizzati con diffrazione di raggi X su cristalli singoli, definendo le loro strutture molecolari con precisione atomica. Poi, le loro proprietà sono state studiate in soluzione (spettrometria di massa, spettroscopia elettronica e NMR, voltammetria ciclica) e in stato solido (spettroscopia Mössbauer, magnetometria DC e AC). Inizialmente, i Cl− assiali sono stati sostituiti con leganti Br− in 1. Il complesso [Fe4(tpda)3Br2] (4) ha interazioni ferromagnetiche dominanti a temperatura ambiente e comportamento magnetico simile ad 1. Sorprendentemente, le misure AC hanno evidenziato una differenza significativa: sebbene sia 1 che 4 abbiano mostrato comportamento da SMM, il rilassamento lento della magnetizzazione in 4 avviene anche in campo zero. Per attivare il meccanismo del doppio scambio, che può rafforzare il ferromagnetismo in composti a valenza mista, 1 è stato ossidato, isolando due complessi lineari a valenza mista: mono- ([Fe2IIFeIII(tpda)3]PF6, 5) e bi-ossidato ([FeIIFe2III(tpda)3Cl]PF6, 6). Gli spettri Mössbauer (57Fe) a temperatura variabile, e quello elettronico, classificano 5 come sistema a valenza mista di tipo Robin-Day Classe II, a 298 K, mentre non si verifica alcuna delocalizzazione a 10 e 77 K. Inoltre, 5 ha comportamento da SMM in campo zero. Per aumentare la stabilità di queste strutture a catena, è stato progettato e sintetizzato un nuovo legante tripodale, N(CH2CH2NH-Py-NH-Py)3, con tre unità oligo--piridilamminiche legate covalentemente tra loro. La sua chimica di coordinazione è stata esplorata preliminarmente con ferro e cobalto, sebbene non siano ancora stati ottenuti nuovi EMAC, fino ad ora.
The annual size of the Global DataSphere (the total amount of data created across the world) has experienced an exponential increase during the last decade, and it will exceed 150 trillion of gigabytes within 2025. Storage, transfer and elaboration of data became one of the most appealing targets in emerging fields such as quantum technologies and spintronics (spin electronics). A primary goal is the control of magnetic properties and spin at the atomic and molecular level. Interesting are specific nanostructures called Single-Molecule Magnets (SMMs), which possess similar magnetic properties to those of bulk magnets but of pure molecular origin. SMMs can feature magnetic bistability and long relaxation times, which make them attractive to be implemented as single bits. Their physical properties can be tuned by chemical design. Iron(II)-based Extended Metal Atom Chains (EMACs) are appealing synthetic targets as SMMs, because of the large spin and magnetic anisotropy of high-spin iron(II). EMACs are linear arrays of at least 3 metal ions wrapped together by polydentate organic ligands, which promote short separations between the metal centers and, sometimes, metal-metal bonds. However, these compounds proved to be very elusive, due to the exceeding tendency of iron(II) to undergo oxidation and hydrolysis processes. In fact, before our report of a tetrairon(II) chain [Fe4(tpda)3Cl2] (1) based on oligo--pyridylamido ligand tpda2– in 2018, the only known iron(II)-based EMAC was a triiron(II) complex with formamidinato ligands (2) described by Cotton et al. in 1998. In 2020, Guillet et al. reported a new triiron(II) chain (3) supported by silylated diaminopyridines. Complexes 1, 2 and 3 exhibit ferromagnetic interactions, while 3 also contains metal-metal bonds. The aim of this Thesis was the design, the synthesis and the characterization of transition metal compounds with highly magnetic electronic states, containing ferromagnetic interactions and, possibly, metal-metal bonds. In particular, it describes a systematic study of a series of iron-based EMACs, obtained and handled in strictly anaerobic and anhydrous conditions. The novel synthesized compounds were firstly characterized by single crystals X-ray diffraction, to define their molecular structures with atomic precision. Afterwards, their properties were investigated in solution (mass spectrometry, electronic and NMR spectroscopy, cyclic voltammetry) and in solid state (Mössbauer spectroscopy, DC and AC magnetometry). The effect of replacing axial Cl– − with Br– ligands in 1 was firstly investigated. Complex [Fe4(tpda)3Br2] (4) exhibits dominant ferromagnetic coupling at room temperature and similar magnetic behavior to 1. Surprisingly, AC experiments pointed out a significant difference: although both 1 and 4 showed SMM behavior, slow magnetic relaxation in 4 was observable even in zero applied field. To attempt activating the double-exchange mechanism, which could strengthen the ferromagnetic interaction in mixed valent compounds, the chemical oxidation of 1 was carried out, isolating two linear triiron mixed-valence species: one- ([Fe2IIFeIII(tpda)3]PF6, 5) and two-electron oxidized ([FeIIFe2III(tpda)3Cl]PF6, 6). Variable temperature 57Fe Mössbauer and electronic spectra suggest that 5 is best classified as a Robin-Day Class II mixed-valence system at 298 K, while no delocalization occurs at 10 and 77 K. Furthermore, 5 exhibits zero-field SMM behavior. In order to better stabilize these chain like structures, a challenging new tripodal ligand, N(CH2CH2NH-Py-NH-Py)3, based on three covalently linked oligo-α-pyridylamido units, was designed and synthesized. Its coordination chemistry towards iron and cobalt was preliminary explored, although no new EMACs were obtained so far.

Cyano-bridged mixed valence compounds have been known since 1704, but a lot of interest in the bi- and tri-nuclear species has emerged only more recently. The growing interest in these complexes reflects their promise as useful applications in electrochromism, molecular magnetism, and molecular electronics. These properties are activated by the excitation of their metal-to-metal charge transfer (MMCT) transition. We have studied aqueous solutions of the FeHEDTA/Fe(CN)64- system that form intensely colored solutions that absorb strongly in the Vis/NIR region. Typically 1:1 dimeric and 2:1 trimeric complexes are formed. We have used optical spectroscopy and electrochemistry to provide information on reorganizational parameters, electronic coupling between metal centers, molar absorptivities, equilibrium constants, and delocalization factors and have compared results obtained for the binuclear and trinuclear species to results of similar systems either previously studied in our lab or found in the literature.