Βασικός στόχος της παρούσης Διπλωματικής Εργασίας ήταν η μελέτη της κρυσταλλικής μηχανικής μίας σειράς συμπλόκων ενώσεων του CoII με ιμιδαζολικά παράγωγα ως υποκαταστάτες και ειδικότερα με το 2-φαινυλοϊμιδαζόλιο και το 4-φαινυλοϊμιδαζόλιο. Η κρυσταλλική μηχανική μπορεί να θεωρηθεί ως ο κλάδος της υπερμοριακής χημείας στη στερεά κατάσταση. Η υπερμοριακή χημεία (supramolecular chemistry) είναι μία από τις πλέον δημοφιλείς και γρήγορα αναπτυσσόμενες περιοχές της πειραματικής χημείας. Χαρακτηρίζεται ως η χημεία των ασθενών διαμοριακών δυνάμεων και εστιάζει στη δομή και λειτουργία των χημικών συστημάτων με υψηλή πολυπλοκότητα (υπερμόρια) που προκύπτουν από το συνδυασμό δύο ή περισσοτέρων διακριτών χημικών ειδών (μορίων, ιόντων) και συγκρατούνται με ασθενείς (και αντιστρεπτές) διαμοριακές δυνάμεις (π.χ. αλληλεπιδράσεις π-π, δεσμούς υδρογόνου, υδρόφοβες αλληλεπιδράσεις, δυνάμεις van der Waals, αλληλεπιδράσεις διπόλου-διπόλου κλπ). Ένα σημαντικό πεδίο της υπερμοριακής χημείας είναι αυτό της κρυσταλλικής μηχανικής (crystal engineering) που αναφέρεται στη στρατηγική σχεδιασμού ενός κρυσταλλικού υλικού με επιθυμητές ιδιότητες και βασίζεται στην κατανόηση και τον έλεγχο των διαμοριακών αλληλεπιδράσεων των μορίων στην κρυσταλλική κατάσταση. Στην παρούσα Διπλωματική Εργασία πραγματοποιήθηκε η σύνθεση συμπλόκων ενώσεων με γενικό τύπο ΜΙΙ/Χ-/L ή L', όπου ΜΙΙ = CoII, X- = Cl-, I-, SCN-, NO3-, L = 2-φαινυλοϊμιδαζόλιο και L' = 4-φαινυλοϊμιδαζόλιο. Με μεταβολή των σημαντικότερων συνθετικών παραμέτρων –γραμμομοριακή αναλογία μετάλλου:υποκαταστάτη, πολικότητα του διαλύτη (MeOH, MeCN, Me2CO, CH2Cl2, CHCl3), συνθήκες θερμοκρασίας και μέθοδο κρυστάλλωσης– απομονώσαμε και χαρακτηρίσαμε τα εξής σύμπλοκα: [CoCl2L2] (1), [CoI2L2] (2), [Co(NCS)2L2] (3), [Co(NO3)2L2] (4), [CoL'4(MeCN)(H2O)](NO3)2 (5), [CoL'4(MeCN)(H2O)]I2 (6), [Co(NCS)2L'2] (7), [Co(NCS)2L'4]•MeOH (8•MeOH). Όπως διαπιστώθηκε με την βοήθεια της κρυσταλλογραφικής ανάλυσης ακτίνων Χ επί μονοκρυστάλλων των ανωτέρω συμπλόκων, οι διαμοριακές αλληλεπιδράσεις που είναι υπεύθυνες για την υπερμοριακή οργάνωση των δομών τους είναι ισχυροί και ασθενείς δεσμοί υδρογόνου και αλληλεπιδράσεις τύπου π-π. Ειδικότερα, τα δεδομένα για τα σύμπλοκα με τον L διαπιστώθηκε ότι: • Σταθερά μοτίβα διαμοριακών αλληλεπιδράσεων (συνθόνια) σχηματίζονται μεταξύ των τεκτονίων N-H των ιμιδαζολικών δακτυλίων και των ενταγμένων ιόντων X (X = Cl, I, NO3, SCN) όλων των συμπλόκων οδηγώντας σε μονο- ή δισδιάστατες δομές. Οι δομές αυτές ενισχύονται περαιτέρω από ασθενείς αλληλεπιδράσεις C-H∙∙∙X (X= Cl, I, O, S) προς 3D υπερμοριακές δομές. • Εκτός του συμπλόκου 2 στο οποίο παρατηρούνται ενδομοριακές π-π αλληλεπιδράσεις σε καμία άλλη δομή δεν παρατηρούνται τέτοιες ενδο- ή διαμοριακές αλληλεπιδράσεις. Για τα σύμπλοκα με τον υποκαταστάτη L' διαπιστώθηκε παρόμοια ότι: • Σταθερά μοτίβα διαμοριακών αλληλεπιδράσεων (συνθόνια) σχηματίζονται μεταξύ των τεκτονίων N-H των ιμιδαζολικών δακτυλίων και των ανόργανων ανιόντων X- (X- = NO3-, I-) στα σύμπλοκα 5 και 6 ή του ενταγμένου SCN στα σύμπλοκα 7 και 8•MeOH ή/και πλεγματικών μορίων διαλύτη (σύμπλοκο 8•MeOH), οδηγώντας σε μονο- ή δισδιάστατες δομές. Παρόμοια με τις δομές 1-4, ασθενείς C-H∙∙∙X (X= O, S) αλληλεπιδράσεις οδηγούν τελικά σε συγκρότηση 3D δομών. • Στα σύμπλοκα 7 και 8•MeOH η οργάνωση της δομής ευνοεί παράλληλα το σχηματισμό διαμοριακών π-π αλληλεπιδράσεων. • Στα σύμπλοκα 5 και 6 είναι απαραίτητη η παρουσία αντισταθμιστικών ιόντων στο πλέγμα τους καθώς πρόκειται για κατιοντικά σύμπλοκα του τύπου [CoL'4(MeCN)(H2O)]2+. • Μόνο το σύμπλοκο 8•MeOH περιέχει πλεγματικά μόρια διαλύτη (MeOH) χωρίς να είναι απαραίτητη η παρουσία αντισταθμιστικών ιόντων στο πλέγμα του. Συμπερασματικά, ο κυρίαρχος παράγοντας που καθορίζει την υπερμοριακή οργάνωση των συμπλόκων και των δύο κατηγοριών (δηλ. με υποκαταστάτες τα ισομερή, 2- και 4-φαινυλοϊμιδαζόλιο) είναι τα ισχυρά συνθόνια N-H∙∙∙X (X = Cl, I, NO3, SCN). / The main target of this diploma thesis was the crystal engineering studies of a series of coordination compounds of CoII with substituted imidazoles as ligands and specifically, with 2-phenylimidazole and 4-phenylimidazole. Crystal engineering may be regarded as the solid-state branch of supramolecular chemistry. Supramolecular chemistry is one of the most popular and rapidly developing areas of experimental chemistry. It may be defined as the chemistry of weak intermolecular forces and focuses on the structure and function of chemical systems of high complexity (supermolecules), resulting from the association of two or more discrete chemical species (molecules, ions) held together by weak (and reversible) intermolecular forces (e.g. π-π interactions, hydrogen bonds, hydrophobic interactions, van der Waals forces, dipole-dipole interactions etc). Crystal engineering is an important field of supramolecular chemistry that refers to the design and synthesis of a crystalline material with desired properties, based on the understanding and control of intermolecular interactions in the crystalline state. In this diploma thesis the synthesis of a series of coordination complexes with general formula ΜΙΙ/Χ-/L or L' [ΜΙΙ = CoII, X- = Cl-, I-, SCN-, NO3- and L = 2-phenylimidazole, L' = 4-phenylimidazole] took place. By altering the parameters of synthesis –metal:ligand molar ratio, solvent polarity (MeOH, MeCN, Me2CO, CH2Cl2, CHCl3), temperature, as well as crystallization method– we were able to isolate and study the following complexes: [CoCl2L2] (1), [CoI2L2] (2), [Co(NCS)2L2] (3), [Co(NO3)2L2] (4), [CoL'4(MeCN)(H2O)](NO3)2 (5), [CoL'4(MeCN)(H2O)]I2 (6), [Co(NCS)2L'2] (7), [Co(NCS)2L'4]•MeOH (8•MeOH). As established by the single-crystal X-ray structure determination of the above complexes, the intermolecular interactions responsible for the supramolecular organization of the structures are strong and weak hydrogen bonds, as well as π-π interactions. A detailed study of the complexes with ligand L reveals that: • Supramolecular synthons between the N-H tectons of imidazole rings and the coordinated X ion (X = Cl, I, NO3, SCN) are formed, leading to 1- or 2D structures, which are further enhanced by weak C-H∙∙∙X (X= Cl, I, O, S) interactions, leading to 3D supramolecular architectures. • There are no intra- or intermolecular π-π interactions observed in complexes 1-4, with the exception of one such intramolecular interaction in complex 2. A detailed study of the complexes with ligand L' reveals that: • Supramolecular synthons between the N-H tectons of imidazole rings and the inorganic anions X- (X- = NO3-, I-) of complexes 5 and 6 or the coordinated SCN of complexes 7and 8 or/and lattice solvent molecules (complex 8•MeOH) are formed, leading to 1- or 2D structures, further organized in 3D architectures by means of weak C-H∙∙∙X (X= O, S) interactions. • In certain complexes (7 and 8•MeOH) the disposition of the complexes favors the formation of intermolecular π-π interactions. • In complexes 5 and 6 the presence of counter ions in their crystal structures is necessary since they are cationic complexes with the [CoL'4(MeCN)(H2O)]2+ unit as their structural core. • Only complex 8•MeOH contains lattice solvent molecules (MeOH) without the presence of counter ions in its crystal lattice. In conclusion, the determining factor of the supramolecular organization of the two series of complexes, that is with the isomers 2- and 4-phenylimidazole as ligands, is the presence of the strong synthons N-H∙∙∙X (X = Cl, I, NO3, SCN).

O presente trabalho apresenta estudos espectrofotométricos relacionados à autoxidação dos complexos de Cu(II), Ni(II) e Co(II)/tetraglicina induzida por sulfito. Nossos estudos verificaram que a autoxidação de Cu(II)/tetraglicina (1,0x10-3 mol L-1) em pH = 9,0 (tampão borato) é afetada pela presença de traços de Ni(II) ou Co(II). Na ausência de Ni(II) ou Co(II), a reação é muito ineficiente e lenta com períodos de indução longos (aproximadamente 4 h). Ni(II) ou Co( II) em concentrações baixas ( 10-5 - 10-6 mol L-1) afetam significativamente a cinética: o período de indução diminui drasticamente (a menos de 2 s) e a formação de Cu(III) é fortemente acelerada com simultâneo aumento da eficiência da reação. A atividade catalítica e o sinergismo positivo de Co(II) e Ni(II) podem ser explicados pela oxidação mais rápida de Co(II) ou Ni(II)/tetraglicina pelo oxigênio dissolvido. O processo eletroquímico relacionado aos sistemas Cu(II)/Cu(III)/tetraglicina e Ni(II)/Ni(III)/tetraglicina são reversíveis, possibilitando monitorá-los adequadamente mediante o uso da técnica de eletrodo rotativo disco-anel. Entretanto, o sistema Co(II)/Co(III)/tetraglicina é irreversível. Esses estudos mostraram que as espécies de Cu(III) e Ni(III) geradas no eletrodo disco são instáveis nas condições experimentais empregadas. O efeito sinérgico positivo na presença de Ni(II) (que permitiu aumentar a sensibilidade) foi aproveitado para desenvolvimento de método espectrofotométrico e amperométrico simples e sensível para a determinação indireta de sulfito em meio aquoso. O método espectrofotométrico está baseado na medida de absorbância do complexo de Cu(III)/tetraglicina (gerado na presença de sulfito e traços de Ni(II)) em 365 nm. O método amperométrico em análise por injeção em fluxo baseia-se na medida de corrente (0,1 V vs Ag/AgCl) em função da concentração de Cu(III)/tetraglicina gerado quimicamente, na presença de sulfito e traços de Ni(II). Os métodos desenvolvidos foram empregados para a determinação de S(IV), em vinhos e sucos, após a sua extração da amostra acidificada, os resultados obtidos concordaram com aqueles obtidos pelo método iodométrico. / The present work presents spectrophotometric studies related to the sulfite induced autoxidation of Cu(II), Ni(II) and Co(II)/tetraglycine complexes. The sulfite induced autoxidação of Cu(II)/tetraglycine (1.0x10-3 mol L-1) at pH = 9.0 (borate buffer) is affected by the presence of small quantities of the Ni(II) or Co(II). In the absence of added nickel (II) or cobalt (II), the reaction is very inefficient and slow with one large induction period (about 4 h). Trace amounts of Ni(II) or Co(II) (10-5 - 10-6 M) affect the kinetic significantly: the induction period drastically decreases (less than 2 s) and the formation of Cu(III) is strongly accelerated. The effectiveness of Cu(III) formation becomes much higher. The catalytic activity and the positive synergism of Co(II) and Ni(II) may be explained by the faster oxidation of Co(II) or Ni(II)/tetraglycine complexes by dissolved oxygen. The electrochemistry of Cu(II)/Cu(III)/tetraglycine and Ni(II)/Ni(III)/tetraglycine systems are reversible, such as it was possible to monitor them by using the rotating ring-disk electrode technique. However, the Co(II)/Co(III)/tetraglycine system is irreversible. Those studies showed that the Cu(III) and Ni(III) species generated on the disk electrode are unstable in the employed experimental conditions. The positive sinergistic effect in the presence of Ni(II) (which allowed to increase the sensibility) was taken in advantage for development of one simple and sensitive spectrophotometric and amperometric method for indirect determination of sulfite in aqueous medium. The spectrophotometric method is based on the absorbance measurement of the Cu(III)/tetraglicyne complex (generated in the presence of sulfite and small quantities of Ni(II)) at 365 nm. The amperometric method by flow injection analysis is based on the current measurement (0.1 V vs Ag/AgCl) as function of Cu(III)/tetraglycine concentration chemically generated, in the presence of sulfite and Ni(II). The methods were employed for the determination of S(IV), in wines and juices, after its extraction from acidified samples and the results were in agreement with those obtained by the iodometric procedure.

O presente trabalho apresenta estudos espectrofotométricos relacionados à autoxidação dos complexos de Cu(II), Ni(II) e Co(II)/tetraglicina induzida por sulfito. Nossos estudos verificaram que a autoxidação de Cu(II)/tetraglicina (1,0x10-3 mol L-1) em pH = 9,0 (tampão borato) é afetada pela presença de traços de Ni(II) ou Co(II). Na ausência de Ni(II) ou Co(II), a reação é muito ineficiente e lenta com períodos de indução longos (aproximadamente 4 h). Ni(II) ou Co( II) em concentrações baixas ( 10-5 - 10-6 mol L-1) afetam significativamente a cinética: o período de indução diminui drasticamente (a menos de 2 s) e a formação de Cu(III) é fortemente acelerada com simultâneo aumento da eficiência da reação. A atividade catalítica e o sinergismo positivo de Co(II) e Ni(II) podem ser explicados pela oxidação mais rápida de Co(II) ou Ni(II)/tetraglicina pelo oxigênio dissolvido. O processo eletroquímico relacionado aos sistemas Cu(II)/Cu(III)/tetraglicina e Ni(II)/Ni(III)/tetraglicina são reversíveis, possibilitando monitorá-los adequadamente mediante o uso da técnica de eletrodo rotativo disco-anel. Entretanto, o sistema Co(II)/Co(III)/tetraglicina é irreversível. Esses estudos mostraram que as espécies de Cu(III) e Ni(III) geradas no eletrodo disco são instáveis nas condições experimentais empregadas. O efeito sinérgico positivo na presença de Ni(II) (que permitiu aumentar a sensibilidade) foi aproveitado para desenvolvimento de método espectrofotométrico e amperométrico simples e sensível para a determinação indireta de sulfito em meio aquoso. O método espectrofotométrico está baseado na medida de absorbância do complexo de Cu(III)/tetraglicina (gerado na presença de sulfito e traços de Ni(II)) em 365 nm. O método amperométrico em análise por injeção em fluxo baseia-se na medida de corrente (0,1 V vs Ag/AgCl) em função da concentração de Cu(III)/tetraglicina gerado quimicamente, na presença de sulfito e traços de Ni(II). Os métodos desenvolvidos foram empregados para a determinação de S(IV), em vinhos e sucos, após a sua extração da amostra acidificada, os resultados obtidos concordaram com aqueles obtidos pelo método iodométrico. / The present work presents spectrophotometric studies related to the sulfite induced autoxidation of Cu(II), Ni(II) and Co(II)/tetraglycine complexes. The sulfite induced autoxidação of Cu(II)/tetraglycine (1.0x10-3 mol L-1) at pH = 9.0 (borate buffer) is affected by the presence of small quantities of the Ni(II) or Co(II). In the absence of added nickel (II) or cobalt (II), the reaction is very inefficient and slow with one large induction period (about 4 h). Trace amounts of Ni(II) or Co(II) (10-5 - 10-6 M) affect the kinetic significantly: the induction period drastically decreases (less than 2 s) and the formation of Cu(III) is strongly accelerated. The effectiveness of Cu(III) formation becomes much higher. The catalytic activity and the positive synergism of Co(II) and Ni(II) may be explained by the faster oxidation of Co(II) or Ni(II)/tetraglycine complexes by dissolved oxygen. The electrochemistry of Cu(II)/Cu(III)/tetraglycine and Ni(II)/Ni(III)/tetraglycine systems are reversible, such as it was possible to monitor them by using the rotating ring-disk electrode technique. However, the Co(II)/Co(III)/tetraglycine system is irreversible. Those studies showed that the Cu(III) and Ni(III) species generated on the disk electrode are unstable in the employed experimental conditions. The positive sinergistic effect in the presence of Ni(II) (which allowed to increase the sensibility) was taken in advantage for development of one simple and sensitive spectrophotometric and amperometric method for indirect determination of sulfite in aqueous medium. The spectrophotometric method is based on the absorbance measurement of the Cu(III)/tetraglicyne complex (generated in the presence of sulfite and small quantities of Ni(II)) at 365 nm. The amperometric method by flow injection analysis is based on the current measurement (0.1 V vs Ag/AgCl) as function of Cu(III)/tetraglycine concentration chemically generated, in the presence of sulfite and Ni(II). The methods were employed for the determination of S(IV), in wines and juices, after its extraction from acidified samples and the results were in agreement with those obtained by the iodometric procedure.

PhD thesis - Faculty of Science / The main aim of this thesis has been to study the way in which Fe(III) and Co(II) incorporation into Si-MCM-41 synthesis gels affects the properties of the unmodified material. Another aim was to investigate the influence of these hetero-atoms on the dispersion and particle size distribution as well as the catalytic activity of supported Au nanoparticles in the CO oxidation reaction. Si-MCM-41 has been successfully synthesized in this work using mixtures containing CTAB as a structure-directing agent (SDA) and water-glass as a SiO2 source. Replacement of water-glass with pre-calcined Si-MCM-41 for SiO2 source in the secondary synthesis step has produced Si-MCM-41 with improved structural properties (XRD, HRTEM and Raman spectroscopy), including restructured and more crystalline pore walls (Raman spectroscopy). The conventional shortcomings of Si-MCM-41 as a support for catalyticallyactive (transition) metal components such as low hydrothermal stability, low PZC, lack of cation exchange capacity and no reducibility have been partially addressed by modification with Fe(III) and Co(II). The premodification was achieved both during framework synthesis and after synthesis by the incipient wetness impregnation (IWI) method. As opposed to the one-pot synthesis of metal-containing derivatives, the IWI method gave materials with high metal loadings and maximal retention of the properties of pristine Si-MCM-41. On the other hand, metal incorporation during synthesis to a loading of ~8.8 wt% using aqueous solutions of metal precursors showed some collapse of the mesostructure. Consequently methods were sought to incorporate this amount of metal (and up to double, i.e., 16 wt%) with maximal retention of the MCM-41 characteristics. These methods included (i) using Si-MCM-41 as a SiO2 source, (ii) dissolving the metal precursors in an acid solution before inclusion into the synthesis gel, and (iii) using freshly precipitated alkali slurries of the metal precursors. The first method produced a highly ordered 16wt% Fe-MCM-41 material with excellent reducibility (TPR showed three well-resolved peaks) and pore-wall structure (Raman spectroscopy). Like the aqueous route, the acid-mediated metal incorporation route did not produce ordered materials at metal contents of ~16 wt%. The base precipitate route produced highly ordered composite materials up to 16 wt% metal content, with characteristics similar to those of Si-MCM-41 (XRD, BET and HRTEM), although some metal phases were observed as a separate phase on the SiO2 surface. Thus, metal-containing MCM-41 materials could be obtained with conservation of MCM-41 mesoporosity. Raman spectroscopic studies have shown that the effect of transition metal incorporation in MCM-41-type materials is to strengthen the pore walls (shift of Si-O-Si peaks to higher frequencies), while TPR studies revealed that the essentially neutral framework of Si-MCM-41 could be rendered reducible by transition metal incorporation. Gold-containing mesoporous nanocomposites were prepared by both direct synthesis and post-synthetically. Catalysts prepared by direct hydrothermal synthesis were always accompanied by formation of large Au particles because of the need to calcine the materials at 500 oC in order to remove the occluded surfactant template. The presence of transition metal components in Me-MCM-41 (Me = Fe and Co) has been found to play a significant role in the particle size distribution and also the dispersion of Au nanoparticles when these materials were used as supports. In general, a base metal-containing support was found to produce smaller Au nanoparticles than the corresponding siliceous support. It has been proposed that the transition metal components serve as anchoring or nucleation sites for the Au nanoparticles, which are likely to sinter during calcination. The anchoring sites thus retard the surface mobility of Au at calcination temperatures above their TTammann. The use of the Au/Me-MCM-41 materials as catalysts in the CO oxidation reaction has led to the following observations: (i) catalyst on metal-containing supports showed better activity than those on Si-MCM-41, probably due to the induced reducibility in metal-MCM-41, (ii) catalysts prepared by direct synthesis showed inferior activity owing to large Au particles, (iii) increasing Au content improves the catalytic performance, (iv) increasing the Fe content of the support at constant Au improves the catalytic performance, and (v) changing the base metal component of the support from Fe to Co led to a significant improvement in catalytic activity. The similarity of the apparent activation energies (Ea) for the 5 wt% Au-containing 5 wt% Fe- and 5 wt% Co-MCM-41 suggested that the difference in catalytic activity is associated with the number of active sites possessed by each catalyst system. The observed order of catalytic activity of these 5 wt% Au-containing systems in terms of the support type is: Co-MCM-41 > Fe-MCM-41 > Si-MCM-41. This was further supported by the average Au particle size, which, in terms of the support, followed the order Co-MCM-41 < Fe-MCM-41 < Si-MCM-41. Thus, metal-support interactions between Au and MCM-41 have been enhanced by introducing Fe(III) and Co(II), which also induced framework charge, ion exchange capacity (IEC) and reducibility in the neutral siliceous support.

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

No description available.

Tese de mestrado integrado. Engenharia Química. Faculdade de Engenharia. Universidade do Porto. 2013

This work comprises two main parts. The first part outlines our efforts to expand on the recent work of Gütlich et.al. by synthesizing Co(II) based spin crossover systems within a dendritic framework. We wanted to investigate the possibility of synthesizing different first generation, triazole containing dendrimers using “click” type reactions and their coordination ability with Co(II) ions. To this end we have had limited success mainly due to the numerous challenges in synthesizing a pure dendrimer product. The second part details our efforts in the synthesis of a mononuclear Co(II) based single molecule magnet. This comes as an extension to recent reports by Chang and Long where they have successfully obtained mononuclear Fe(II) single molecule magnets by inducing structural distortions within the complexes to amplify the spin-orbit coupling. We postulated that the use of Co(II) in conjunction with a bulky ligand framework would lead to desirable magnetic properties. We chose the known bis(imino)pyridine ligand scaffold due to its rich chemistry and its interesting and unexpected coordination behaviour, as we have seen in previous research efforts by our lab. To this end we were successful in isolating and characterizing 4 compounds, and we have carried out detailed magnetic measurements on the two most magnetically interesting species.

This work comprises two main parts. The first part outlines our efforts to expand on the recent work of Gütlich et.al. by synthesizing Co(II) based spin crossover systems within a dendritic framework. We wanted to investigate the possibility of synthesizing different first generation, triazole containing dendrimers using “click” type reactions and their coordination ability with Co(II) ions. To this end we have had limited success mainly due to the numerous challenges in synthesizing a pure dendrimer product. The second part details our efforts in the synthesis of a mononuclear Co(II) based single molecule magnet. This comes as an extension to recent reports by Chang and Long where they have successfully obtained mononuclear Fe(II) single molecule magnets by inducing structural distortions within the complexes to amplify the spin-orbit coupling. We postulated that the use of Co(II) in conjunction with a bulky ligand framework would lead to desirable magnetic properties. We chose the known bis(imino)pyridine ligand scaffold due to its rich chemistry and its interesting and unexpected coordination behaviour, as we have seen in previous research efforts by our lab. To this end we were successful in isolating and characterizing 4 compounds, and we have carried out detailed magnetic measurements on the two most magnetically interesting species.

This work comprises two main parts. The first part outlines our efforts to expand on the recent work of Gütlich et.al. by synthesizing Co(II) based spin crossover systems within a dendritic framework. We wanted to investigate the possibility of synthesizing different first generation, triazole containing dendrimers using “click” type reactions and their coordination ability with Co(II) ions. To this end we have had limited success mainly due to the numerous challenges in synthesizing a pure dendrimer product. The second part details our efforts in the synthesis of a mononuclear Co(II) based single molecule magnet. This comes as an extension to recent reports by Chang and Long where they have successfully obtained mononuclear Fe(II) single molecule magnets by inducing structural distortions within the complexes to amplify the spin-orbit coupling. We postulated that the use of Co(II) in conjunction with a bulky ligand framework would lead to desirable magnetic properties. We chose the known bis(imino)pyridine ligand scaffold due to its rich chemistry and its interesting and unexpected coordination behaviour, as we have seen in previous research efforts by our lab. To this end we were successful in isolating and characterizing 4 compounds, and we have carried out detailed magnetic measurements on the two most magnetically interesting species.