Diploma thesis deals with preparation of peripherally functionalized polydentate Schiff ligands, suitable for metal coordination, such as Fe(III) or Co(III). The compounds, formed by this functionalization using organic molecule or stable organic radical, provide coordination site for another central atom. The compounds were synthesized for their potential biological activity. The organic ligands series was prepared, and these ligands were submitted to coordination reactions with selected transition metals. The prepared compounds were characterized by nuclear magnetic resonance, mass spectrometry, electron paramagnetic resonance and X-ray structure analysis.

Three cobalt-based oxides operating at the Co(III)/Co(II) redox couple have been investigated as potential cathode materials for the intermediate-temperature solid oxide fuel cells (IT-SOFCs). X-ray absorption spectroscopy measurements confirmed that both the oxygen-deficient perovskite Sr[subscript 0.7]Y[subscript 0.3]CoO[subscript 2.65-delta] (SYCO) and the double-perovskite Ba₂[Co][Bi[subscript x]Sc[subscript 0.2]Co[subscript 1.8-x]][subscript O6-delta] (x = 0.1 and 0.2) (BBSC) contain high-spin Co(III) in the bulk at room temperature and thus avoid the thermally driven spin-state crossover of the Co(III) ions usually observed in other cobalt-containing perovskite oxides. Electrochemical characterizations demonstrated that both cobalt oxides operating on the Co(III)/Co(II) redox couple are equally catalytically active for the oxygen reduction reaction as those operating on the Co(IV)/Co(III) redox couple. With an LSGM electrolyte-supported single test cell and NiO+GDC as anode, the maximum power densities Pmax at 800 ºC reach 927 and 1180 mW·cm⁻² for SYCO and BBSC cathodes, respectively. The oxygen-deficient perovskites Sr[subscript 1-x]R[subscript x]CoO[subscript 3-delta] (R = Eu-Ho, Y, x [approximately equal] 0.3) are identified as a new class of cathode materials for IT-SOFCs in this dissertation. On the other hand, the layered Ba2Co9O14 (BCO) containing the low-spin Co(III) at room temperature undergoes a thermally driven spin-state crossover, which has prevented it from being evaluated as the cathode of IT-SOFCs. This problem was overcome by fabrication of a 50-50 wt.% BCO + SDC (Sm[subscript 0.2]Ce[subscript 0.8]O[subscript 1.9]) composite cathode. The addition of SDC not only improved the adhesion to the electrolyte, but also enhanced the electrocatalytic activity for the oxygen reduction reaction. The composite cathode delivers a nearly stable P[subscript max] of ~450 mW·cm-2 at 800 °C in an LSGM electrolyte-supported single test cell. In addition, the electrochemical lithium intercalation process in the monoclinic Nb12O29 was studied with a Li/Nb₁₂O₂₉ half-cell, and the results showed that it can reversibly incorporate a relatively large amount of Li-ions in the voltage window of 2.5-1.0 V at a slow discharge/charge rate while retaining structural integrity. Compared with that of the bare Nb₁₂O₂₉, samples with carbon coating show an improved rate capability. The lithium insertion mechanism into Nb₁₂O₂₉ has also been discussed in terms of sites available to the lithium ions / text

Photoelectron spectroscopy is an experimental method to study the electronic structure in matter. In this thesis, a combination of soft and hard X-ray based photoelectron spectroscopy has been used to obtain atomic level understanding of electronic structures and energy level alignments in mesoscopic solar cells. The thesis describes how the method can be varied between being surface and bulk sensitive and how to follow the structure linked to particular elements. The results were discussed with respect to the material function in mesoscopic solar cell configurations. The heart of a solar cell is the charge separation of photoexcited electrons and holes, and in a mesoscopic solar cell, this occurs at interfaces between different materials. Understanding the energy level alignment between the materials is important for developing the function of the device. In this work, it is shown that photoelectron spectroscopy can be used to experimentally follow the energy level alignment at interfaces such as TiO2/metal sulfide/polymer, as well as TiO2/perovskite. The electronic structures of two perovskite materials, CH3NH3PbI3 and CH3NH3PbBr3 were characterized by photoelectron spectroscopy and the results were discussed with support from quantum chemical calculations. The outermost levels consisted mainly of lead and halide orbitals and due to a relatively higher cross section for heavier elements, hard X-ray excitation was shown useful to study the position as well as the orbital character of the valence band edge. Modifications of the energy level positions can be followed by core level shifts. Such studies showed that a commonly used additive in mesoscopic solar cells, Li-TFSI, affected molecular hole conductors in the same way as a p-dopant. A more controlled doping can also be achieved by redox active dopants such as Co(+III) complexes and can be studied quantitatively with photoelectron spectroscopy methods. Hard X-rays allow studies of hidden interfaces, which were used to follow the oxidation of Ti in stacks of thin films for conducting glass. By the use of soft X-rays, the interface structure and bonding of dye molecules to mesoporous TiO2 or ZnO could be studied in detail. A combination of the two methods can be used to obtain a depth profiling of the sample.

Au cours de ce travail de thèse, nous avons montré le rôle du ligand organique pour moduler les propriétés électroniques de complexes de métaux de transition mono- et polynucléaires.<br />La première partie de ce travail étudie tout d'abord l'influence des effets électroniques (donneurs et accepteurs) des ligands chélatants sur les propriétés électrochimiques de complexes mononucléaires de Fe(III). Nous avons également montré qu'il est possible de moduler les propriétés optiques de complexes polynucléaires à valence mixte FeIIBS(FeIIIHS)x (x = 4 et 6). Enfin, un modèle a été proposé pour expliquer l'origine de l'interaction ferromagnétique au sein d'un des premiers composés de la chimie de coordination, le bleu de Prusse dont les complexes FeIIBS(FeIIIHS)x sont des modèles.<br />La deuxième partie concerne l'étude de l'anisotropie magnétique au sein de complexes mononucléaires de Ni(II). Ce travail montre qu'il est possible d'influencer l'amplitude et la nature (axiale, planaire ou rhombique) de l'anisotropie magnétique grâce au choix des ligands chélatants.<br />Enfin, une modulation de l'énergie des états de spin de systèmes binucléaires en jouant sur les ligands pontants et périphériques permet de mettre en évidence le croisement de deux niveaux MS issus de deux états S différents sous l'action d'un champ magnétique extérieur. Ainsi il est possible d'accéder aux propriétés d'anisotropie dans les états excités de complexes polynucléaires possédant un état fondamental de spin S = 0.