No description available.

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.

No description available.

To better understand the optical and electronic properties of thiophene- and pyrrole-based organic compounds on a molecular level, several aromatic compounds and their corresponding monocations were analyzed by a variety of solution-based spectroscopic techniques. The derivatives were initially synthesized using palladium-catalyzed amination reactions, condensation reactions, Horner-Emmons reactions, and Stille coupling reactions. Once isolated, the neutral compounds were analyzed by UV-visible-NIR absorption spectroscopy, fluorescence spectroscopy, cyclic voltammetry, and / or differential pulse voltammetry. Monocations were generated by chemical oxidation and were analyzed by visible-NIR absorption spectroscopy and electron paramagnetic resonance spectroscopy. By quantifying the extent of the electron-donor abilities of some chromophores and the electron delocalization of positive charge in the monocations, a more thorough understanding of the optical and electronic properties of the compounds was obtained.

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.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20201号 / 理博第4286号 / 新制||理||1616(附属図書館) / 京都大学大学院理学研究科化学専攻 / (主査)教授 北川 宏, 教授 竹腰 清乃理, 教授 島川 祐一 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

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.

Copper (Cu) compounds are widely used as effective agricultural bactericides. Continuous use of these materials has led to Cu accumulation in soil over time. The United States Environmental Protection Agency (US EPA) is concerned about potential Cu contamination in the environment. Improving biocidal efficacy of Cu is an attractive alternative, allowing reduction of Cu amount per application. In this research, we focused on making watersoluble mixed-valence Copper/Silica composite nanogel (CuSiNG) material. The objective is to improve the efficacy of Cu by manipulating Cu valence states. It has been shown in the literature that Cu (0) and Cu (I) states are more potent that Cu (II) states in terms of their antimicrobial efficacy. It is hypothesized that mixed valence Cu will exhibit improved efficacy over Cu (II). A water-soluble mixed valence Cu/silica nanogel (MV-CuSiNG) composite has been synthesized and characterized. Structure, morphology, crystallinity and composition of the MV-CuSiNG material was characterized using High-Resolution Transmission Electron Microscopy (HRTEM), HRTEM Selected Area Electron Diffraction (SAED) and X-ray Photoelectron Spectroscopy (XPS). Amount of Cu loading in MV-CuSiNG composite material was estimated by Atomic Absorption Spectroscopy (AAS). To confirm presence of Cu (I) in the MV-CuSiNG material, Neocuproine (Nc, a Cu (I) specific chelator) assay was used. Antimicrobial efficacy of MVCuSiNG and CuSiNG was evaluated against X.alfalfae, B.subtilis and E.coli using Kocide® 3000 ("Insoluble Cu (II)" compound), Copper sulfate ("Soluble Cu (II)" compound) and Cuprous chloride (Copper (I) compound) as positive controls and silica "seed" particles (without Cu loading) as negative control. Antimicrobial studies included observing bacterial growth inhibition and determining the Minimum Inhibitory Concentration (MIC). Improved antimicrobial efficacy was observed in MV-CuSiNG when compared to CuSiNG and other controls. For the assessment of plant safety of MV-CuSiNG and CuSiNG materials, phytotoxicity studies were conducted using Vinca sp and Hamlin orange under environmental conditions. It was observed that MV-CuSiNG material was safe to plants at commercially used

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.

No description available.