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Thesis (Ph. D.)--Joint Program in Chemical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2009. / Includes bibliographical references. / The application of elemental and isotopic metal palaeoredox tracers to the geologic past rests on an understanding of modern metal cycles. This study reevaluates the surface-cycling of Mo and Re in near-surface reservoirs. Revised river averages of Mo and Re are 1.8- and 7.9-fold larger than previous estimates. The river concentrations of 8.0 nmol Mo kg-1 and 11.2 pmol Re kg- (pre-anthropogenic), result in shorter seawater response times of 4.4 x 105 yr ([Tau]Mo) and 1.3 x 105 yr ([Tau]Re pre-anthropogenic). These metals, especially Re, are more sensitive to changing source and sink fluxes than previously thought. Evaluation of Mo and Re concentrations in high temperature fluids from the Manus Basin indicate that Re is essentially absent from the hydrothermal end member and Mo is present at concentrations considerably lower than ambient seawater. The sink fluxes represented by hydrothermal circulation are negligible in comparison to the revised river source fluxes. Anthropogenic contributions to the Re flux to seawater are seen in the high concentrations of certain impacted water samples such as those associated with mining sites. It may also be seen in a significant, variable, Re enrichment feature in the Hudson River estuary. This Re enrichment feature is not the result of estuarine mixing or the remobilization of sediment-hosted Re. On the basis of a Re - SO2- correlation we are able to quantify and correct for the anthropogenic Re, which corresponds to ~33% of the modern river average. This study documents the development of an analytical method for stable Re isotopes. / (cont.) Though complicated by analyte requirements and 187Re 1870s decay, Re isotope measurements have a reproducibility of ±0.05%o for analyte concentrations of 20 ng Re mL-1. Total Re isotopic variability to date is 0.9%o. This includes 0.3%0 across five commercially available Re products, and 0.5%0 across a black shale weathering profile. 6187Re variability across the weathering profile was systematic with the most weathered samples showing the most significant [delta]187Re depletions. The Re isotopic weathering profile is well described by both two-component mixing and Rayleigh fractionation. There are currently insufficient data to discriminate between the two models. / by Christian Alexander Miller. / Ph.D.

Borides are implemented in a range of industrial applications due to their unique mechanical, electrical, thermal and catalytic properties. In particular, transition metal diborides are of special interest. In the recent years, borides of rhenium (Re), osmium (Os) and iridium (Ir) have been studied as for their ultra-hardness and superior stiffness. In this dissertation, a mechanochemical method is introduced to produce rhenium diboride (ReB2) powder, a novel hexagonal osmium diboride (h-OsB2), and iridium boride powders. Densification by Spark Plasma Sintering (SPS), thermal stability and mechanical properties of h-OsB2 were also studied. ReB2 was recently reported to exhibit high hardness and low compressibility, which both are strong functions of its stoichiometry, namely Re to B ratio. Most of the techniques used for ReB2 synthesis reported 1:2.5 Re to B ratio because of the loss of the B during high temperature synthesis. However, as a result of B excess, the amorphous boron, located along the grain boundaries of polycrystalline ReB2, would degrade the ReB2 properties. Therefore, techniques which could allow synthesizing the stoichiometric ReB2 preferably at room temperature are in high demand. ReB2 powder was synthesized at low temperature using mechanochemical route by milling elemental crystalline Re and amorphous B powders in the SPEX 8000 high energy ball mill for 80 hours. The formation of boron and perrhenic acids are also reported after ReB2 powder was exposed to the moist air environment for a twelve month period of time. Hexagonal osmium diboride (h-OsB2), a theoretically predicted high-pressure phase, has been synthesized for the first time by a mechanochemical method, i.e., high energy ball milling. X-ray diffraction (XRD) indicated the formation of h-OsB2 after 2.5 hours of milling, and the reaction reaches equilibrium after 18 hours of milling. The lattice parameters of the h-OsB2 are a=2.916Å and c=7.376 Å, with a P63/mmc space group. Transmission electron microscopy confirmed the appearance of the h-OsB2 phase. The thermal stability of h-OsB2 powder was studied by heating under argon up to 876 °C and cooling in vacuo down to -225 °C. The oxidation mechanism of h-OsB2 has also been proposed. The hexagonal phase partially converted to the orthorhombic phase (20 wt.%) after spark plasma sintering of h-OsB2 at 1500°C and 50MPa for 5 minutes. Hardness and Young*s modulus of the h-OsB2 were measured to be 31 ± 9 GPa and 574 ± 112 GPa, respectively by nanoindentation method. Prior to this research a number of compounds have been prepared in Ir-B system with lower than 2 boron stoichiometry, and no IrB2 phases have been synthesized experimentally. In this dissertation, three new iridium boride phases, ReB2-type IrB2, AlB2-type IrB2 and IrB have been synthesized with a similar mechanochemical method. The formation of these three phases has been confirmed by both X-ray diffraction (XRD) and transmission electron microscope (TEM) after 30 hours of ball milling and 48 hours of annealing. The IrB2 phases have hexagonal crystal structures and the new IrB phase has an orthorhombic crystal structure. The segregation of iridium from iridium borides* lattices has also been studied by high resolution TEM.

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No description available.

No description available.

<p>A series of new methodologies to link a neurotransmitter receptor targeting vector (WAY) to carboranes and the preparation of the corresponding metallocarboranes (M = Re, ^99mTc) as a new class of organometallic CNS imaging probes is described. WAY-carboranes (<strong>5</strong>, <strong>6</strong>, <strong>16</strong>) and the corresponding metallocarboranes (M = Re (<strong>12</strong>, <strong>13</strong>, <strong>22a</strong>, <strong>22b</strong>), ^99mTc (<strong>14a</strong>, <strong>15</strong>, <strong>23</strong>)) were synthesized in yields ranging from 10-95%. The first observed 3,1,2 versus 2,1,8 rhenacarborane isomerization process was discovered for <strong>12</strong> where isomerization and complexation occurred simultaneously. Re-carboranes <strong>22a</strong> and <strong>22b</strong> had similar carbon-carbon cage configuration where electronic effects was the driving force behind isomerization.</p> <p>The lipophilicities of ^99mTc-carboranes (<strong>14a</strong>, <strong>15</strong>, <strong>23)</strong> were within the ideal range to cross the BBB (log P = 2.4-2.6). <em>In vitro</em> binding data showed that <strong>22b</strong> has high affinity for alpha-adrenergic receptors (K_i = 17-39 nM) resulting in the first organometallic complex to effectively bind to this class of receptors. SPECT images of <strong>14a</strong> in rats showed no brain uptake, while quantitative biodistribution studies indicated modest, non-negligible brain uptake in the hypothalamus region.</p> <p>The neutral [M(CO)₂(NO)(C₂B₉H₁₀R)] analogues (<strong>30</strong>, <strong>34</strong>, <strong>37</strong>) were prepared to address the limited brain uptake of the [M(CO)₃(C₂B₉H₁₀R)]^- complexes. Reactivity differences between Re and ^99mTc were noted during nitrosation conditions where the initial products from the reaction led to nitration of the phenyl group in addition to nitrosation of the metal core. The fluorescence properties of <strong>29</strong> were measured.</p> <p>Low yields and multistep syntheses associated with the preparation of substituted carborane led to the development of a carborane-alkyne platform. Alkyne-carboranes (<strong>53</strong>-<strong>55</strong>) were developed and conjugated to WAY-azide (<strong>46</strong>) using “click” chemistry. The metallocarboranes (M = Re (<strong>69</strong>-<strong>71</strong>), ^99mTc (<strong>72</strong>-<strong>74</strong>)) were generated in yields ranging from 45-71%.</p> / Doctor of Philosophy (PhD)

The phenomenon luminescence rigidochromism has been reported since the 1970s in tricarbonyldiimine complexes with a general formula [R(CO)3LX] using conventional unipolar diimine ligands such as 2,2;-bipyridine or 1,10-phenanthroline as L, and halogens or simple solvents as X. As a major part of this dissertation, microwave-assisted synthesis, purification, characterization and detailed photoluminescence studies of the complex fac-[ReCl(CO)3L], 1, where L = 4-[4,6-bis(3,5-dimethyl-1H-pyrazol-1-yl]-N,N-diethylbenzenamine are reported. The employment of microwaves in the preparation of 1 decreased the reaction time from 48 to 2 hours compared to the conventional reflux method. Stoichiometry variations allows for selective preparation of either a mononuclear, 1, or binuclear, fac-[Re2Cl2(CO)6], 2, complex. The photophysical properties of 1 were analyzed finding that it possesses significant luminescence rigidochromism. The steady state photoluminescence emission spectra of 1 in solution shift from 550 nm in frozen media to 610 nm when the matrix becomes fluid. Moreover, a very sensitive emission spectral analysis of 0.1 K temperatures steps shows a smooth transition through the glass transition temperature of the solvent host. Furthermore, synthetic modifications to L have attained a family of ambipolar compounds that have tunable photophysical, thermophysical and other material properties that render them promising candidates for potential applications in organic electronics and/or sensors - either as is or for their future complexes with various transition metals and lanthanides.

Neste trabalho, foram estudadas as propriedades fotoquímica e/ou fotofísica de alguns compostos de coordenação de rênio(l) e ferro(I I). A irradiação dos complexos fac-[Re(CO)3(NN)(trans-L)]+, NN= 4,7-difenil-1,10- fenantrolina (ph2phen) ou 5-cloro-1,10-fenantrolina (Clphen) e L = 1,2-bis(4-piridil)etileno (bpe) ou 4-estirilpiridina (stpy), em acetonitrila ou em filme de poli(metacrilato de metila) (PMMA) resulta em variações espectrais condizentes com a fotoisomerização trans-cis do ligante coordenado. A determinação dos rendimentos quânticos para a fotorreação pela variação espectral resultou em valores aparentes, uma vez que o reagente e o fotoproduto absorvem na mesma região. Para a determinação do rendimento quântico real, &#934;real, utilizou-se a técnica de 1H RMN, na qual os sinais do fotoproduto e do reagente são observados em regiões distintas com diferentes constantes de acoplamento. Os valores de &#934;real obtidos para fac-[Re(CO)3h(NN)(trans-bpe)]+ (ph2phen: &#934;313= 0,43 ± 0,03; &#934;365= 0,44 ± 0,02; &#934;404= 0,43 ± 0,02; Clphen: &#934;313= 0,56 ± 0,03; &#934;365= 0,55 ± 0,04; &#934;404= 0,57 ± 0,06) são independentes do comprimento de onda de irradiação, indicando a existência de um único canal para a população do estado excitado 3ILtrans-bpe. Por outro lado, para fac-[Re(CO)3(NN)(trans-stpy)]+, os valores de &#934;real sob irradiação a 404 nm são menores que os determinados para os demais comprimentos de onda de irradiação (ph2phen: &#934;313= 0,60 ± 0,05; &#934;365= 0,64 ± 0,09; &#934;404= 0,42 ± 0,03; Clphen: &#934;313= 0,52 ± 0,05; &#934;365= 0,58 ± 0,02; &#934;404= 0,41 ± 0,06), indicando que, a energias maiores, em que o Iigante absorve significativamente, deve existir a contribuição de outro canal para a população do estado excitado 3ILtrans-stpy. A eficiência do fotoprocesso foi avaliada por meio da substituição dos ligantes NN e/ou L, e a diferença nos valores de &#934;real entre os complexos deve estar relacionada principalmente com as distintas eficiências de cruzamento intersistemas. o fotoprocesso altera as propriedades fotofísicas desses complexos. Os isômeros trans apresentam fraca ou nenhuma emissão a 298 K, enquanto os fotoprodutos, fac-[Re(CO)3(NN)(cis-L)]+, apresentam intensa luminescência dominada pelo estado excitado 3MLCTRe&#8594;NN, que é sensivel à rigidez do meio. A reatividade fotoquímica dos pentacianoferratos(II) [Fe(CN)5 (NN)]3-, NN= 2aminobenzilamina (aba), 2-aminobenzamida (ab), 2-(dimetilaminometil)-3-hidroxipiridina (dmampy), 2-aminometilpiridina (ampy), 2-aminoetilpiridina (aepy) ou 2-(2metilaminoetil) piridina (maepy), também foi investigada. A irradiação desses complexos resulta na fotossubstituição do CN-, a qual só pode ser detectada quando o ligante possui um segundo grupo coordenante nas proximidades da esfera de coordenação. Os rendimentos quânticos da fotossubstituição são dependentes do comprimento de onda de irradiação (&#934;313= 0,13 ± 0,01; &#934;334= 0,091 ± 0,001; &#934;365= 0,056 ± 0,002; &#934;404= 0,022 ± 0,002; &#934;436= 0,015 ± 0,001, por exemplo, para NN = aba) e indicam a existência de canais distintos pelos quais a fotorreação ocorre ou as diferentes eficiências de cruzamento intersistema para a população do estado excitado reativo. A eficiência do fotoprocesso também depende do Iigante utilizado (&#955;irr= 365 nm: &#934;aba= 0,056, &#934;ab= 0,14, &#934;ampy= 0,046, &#934;aepy= 0,066, &#934;maepy= 0,069 e &#934;dmampy= 0,12). Na série das diaminas, o rendimento quântico é maior para [Fe(CN)5(ab)]3-, que possui dois sítios para ocorrer o fechamento do anel. Na série das aminopiridinas, observa-se a influência do comprimento da cadeia na eficiência do fechamento do anel. A presença de metilas ligadas ao nitrogênio alifático deve ter pouca ou nenhuma influência na eficiência do fotoprocesso. / The photochemical and/or photophysical properties of some coordination compounds of rhenium(l) and iron(II) were investigated. Photolyses of the fac-[Re(CO)3(NN)(trans-L)+ complexes, NN = 4,7-diphenyl-1, 10- phenanthroline (ph2phen) or 5-chloro-1,10-phenanthroline (Clphen), and L = 1,2-bis(4pyridyl) ethylene (bpe) or 4-styrylpyridine (stpy) in acetonitrile or in poly(methylmethacrilate) (PMMA) films led to spectral changes due to the trans-cis photoisomerization process of the coordinated ligand. Determination of quantum yields for the photoreaction from absorption spectral changes resulted in apparent values once the reactant and the photoproduct absorb in the same region. For the true quantum yields determination, &#934;true, the 1H NMR spectroscopy was employed since the signals of the photoproduct and the reactant are observed in distinct regions with different coupling constants. The &#934;true determined for fac-[Re(CO)3(NN)(trans-bpe)+ (ph2phen: &#934;313= 0.43 ± 0.03; &#934;365= 0.44 ± 0.02; &#934;404= 0.43 ± 0.02; Clphen: &#934;313= 0.56 ± 0.03; &#934;365= 0.55 ± 0.04; &#404= 0.57 ± 0.06) are independent on the irradiation wavelength indicating only one pathway for the 3ILtrans-bpe excited state population. On the other hand, for fac-[Re(CO)3(NN)(trans-stpy)+ the &#934;true under 404 nm irradiation are lower than those determined for the others irradiation wavelengths (ph2phen: &#934;313= 0.58 ± 0.04; &#934;365= 0.64 ± 0.09; &#934;404 =0.42 ± 0.04; Clphen: &#934;313= 0.54 ± 0.02; &#934;365= 0.58 ± 0.03; &#934;404= 0.42 ± 0.06) which indicate that at higher energies, where the ligand absorbs significantly, there is another pathway that contributes to the 3ILtrans-stpy excited state population. The photoprocess efficiency was evaluated by changing the NN and/or L Iigands, and the differences between the &#934;true can be rationalized mainly in terms of distinct intersystem crossing efficiencies.The photoprocess changes the photophysical properties of these complexes. While the trans isomers exhibit week or no emission at 298 K, the photoproducts, fac-[Re(CO)3(NN)(cis-L)]+, exhibit intense emission driven by 3MLCTRe&#8594;NN excited state, which is sensitive to the medium rigidity. The photochemical reactivity of pentacyanoferrate(II) complexes [Fe(CN)5(NN)]3-, NN = 2-aminobenzilamine (aba), 2-aminobenzamide (ab), 2-(dimethylaminomethyl)-3hydroxypyridine (dmampy), 2-amonomethylpyridine (ampy), 2-aminoethylpyridine (aepy), or 2-(2-methylaminoethyl)pyridine (maepy), were also investigated. Irradiation of these complexes results in the CN- photosubstitution which is detected only when the ligand has an additional coordinating group available near the coordination sphere. The photosubstitution quantum yields are dependent on the irradiation wavelength (&#934;313= 0.13 ± 0.01; &#934;334= 0.091 ± 0.001; &#934;365= 0.056 ± 0.002; &#934;404= 0.022 ± 0.002; &#934;436= 0.015 ± 0.001 for NN = aba), indicating the existence of distinct pathways in which the photoreaction takes place or the distinct population of the reactive excited state due to different intersystem crossing efficiencies. The efficiency of the photoprocess is also dependent on the Iigand (&#955;Irr= 365 nm: &#934;aba= 0.056, &#934;ab= 0.14, &#934;ampy= 0.046, &#934;aepy= 0.066, &#934;maepy= 0.069 e &#934;dmampy= 0.12). For the diamines complexes, the higher quantum yield is observed for [Fe(CN)5(ab)]3-, which exhibit two sites to occur the ring closure. For the aminopiridines, it is óbserved the importance of the chain length on the closure ring efficiency. And that the presence of methyl groups attached to the nitrogen has week or no influence on the photoprocess efficiency.

Neste trabalho, foram estudadas as propriedades fotoquímica e/ou fotofísica de alguns compostos de coordenação de rênio(l) e ferro(I I). A irradiação dos complexos fac-[Re(CO)3(NN)(trans-L)]+, NN= 4,7-difenil-1,10- fenantrolina (ph2phen) ou 5-cloro-1,10-fenantrolina (Clphen) e L = 1,2-bis(4-piridil)etileno (bpe) ou 4-estirilpiridina (stpy), em acetonitrila ou em filme de poli(metacrilato de metila) (PMMA) resulta em variações espectrais condizentes com a fotoisomerização trans-cis do ligante coordenado. A determinação dos rendimentos quânticos para a fotorreação pela variação espectral resultou em valores aparentes, uma vez que o reagente e o fotoproduto absorvem na mesma região. Para a determinação do rendimento quântico real, &#934;real, utilizou-se a técnica de 1H RMN, na qual os sinais do fotoproduto e do reagente são observados em regiões distintas com diferentes constantes de acoplamento. Os valores de &#934;real obtidos para fac-[Re(CO)3h(NN)(trans-bpe)]+ (ph2phen: &#934;313= 0,43 ± 0,03; &#934;365= 0,44 ± 0,02; &#934;404= 0,43 ± 0,02; Clphen: &#934;313= 0,56 ± 0,03; &#934;365= 0,55 ± 0,04; &#934;404= 0,57 ± 0,06) são independentes do comprimento de onda de irradiação, indicando a existência de um único canal para a população do estado excitado 3ILtrans-bpe. Por outro lado, para fac-[Re(CO)3(NN)(trans-stpy)]+, os valores de &#934;real sob irradiação a 404 nm são menores que os determinados para os demais comprimentos de onda de irradiação (ph2phen: &#934;313= 0,60 ± 0,05; &#934;365= 0,64 ± 0,09; &#934;404= 0,42 ± 0,03; Clphen: &#934;313= 0,52 ± 0,05; &#934;365= 0,58 ± 0,02; &#934;404= 0,41 ± 0,06), indicando que, a energias maiores, em que o Iigante absorve significativamente, deve existir a contribuição de outro canal para a população do estado excitado 3ILtrans-stpy. A eficiência do fotoprocesso foi avaliada por meio da substituição dos ligantes NN e/ou L, e a diferença nos valores de &#934;real entre os complexos deve estar relacionada principalmente com as distintas eficiências de cruzamento intersistemas. o fotoprocesso altera as propriedades fotofísicas desses complexos. Os isômeros trans apresentam fraca ou nenhuma emissão a 298 K, enquanto os fotoprodutos, fac-[Re(CO)3(NN)(cis-L)]+, apresentam intensa luminescência dominada pelo estado excitado 3MLCTRe&#8594;NN, que é sensivel à rigidez do meio. A reatividade fotoquímica dos pentacianoferratos(II) [Fe(CN)5 (NN)]3-, NN= 2aminobenzilamina (aba), 2-aminobenzamida (ab), 2-(dimetilaminometil)-3-hidroxipiridina (dmampy), 2-aminometilpiridina (ampy), 2-aminoetilpiridina (aepy) ou 2-(2metilaminoetil) piridina (maepy), também foi investigada. A irradiação desses complexos resulta na fotossubstituição do CN-, a qual só pode ser detectada quando o ligante possui um segundo grupo coordenante nas proximidades da esfera de coordenação. Os rendimentos quânticos da fotossubstituição são dependentes do comprimento de onda de irradiação (&#934;313= 0,13 ± 0,01; &#934;334= 0,091 ± 0,001; &#934;365= 0,056 ± 0,002; &#934;404= 0,022 ± 0,002; &#934;436= 0,015 ± 0,001, por exemplo, para NN = aba) e indicam a existência de canais distintos pelos quais a fotorreação ocorre ou as diferentes eficiências de cruzamento intersistema para a população do estado excitado reativo. A eficiência do fotoprocesso também depende do Iigante utilizado (&#955;irr= 365 nm: &#934;aba= 0,056, &#934;ab= 0,14, &#934;ampy= 0,046, &#934;aepy= 0,066, &#934;maepy= 0,069 e &#934;dmampy= 0,12). Na série das diaminas, o rendimento quântico é maior para [Fe(CN)5(ab)]3-, que possui dois sítios para ocorrer o fechamento do anel. Na série das aminopiridinas, observa-se a influência do comprimento da cadeia na eficiência do fechamento do anel. A presença de metilas ligadas ao nitrogênio alifático deve ter pouca ou nenhuma influência na eficiência do fotoprocesso. / The photochemical and/or photophysical properties of some coordination compounds of rhenium(l) and iron(II) were investigated. Photolyses of the fac-[Re(CO)3(NN)(trans-L)+ complexes, NN = 4,7-diphenyl-1, 10- phenanthroline (ph2phen) or 5-chloro-1,10-phenanthroline (Clphen), and L = 1,2-bis(4pyridyl) ethylene (bpe) or 4-styrylpyridine (stpy) in acetonitrile or in poly(methylmethacrilate) (PMMA) films led to spectral changes due to the trans-cis photoisomerization process of the coordinated ligand. Determination of quantum yields for the photoreaction from absorption spectral changes resulted in apparent values once the reactant and the photoproduct absorb in the same region. For the true quantum yields determination, &#934;true, the 1H NMR spectroscopy was employed since the signals of the photoproduct and the reactant are observed in distinct regions with different coupling constants. The &#934;true determined for fac-[Re(CO)3(NN)(trans-bpe)+ (ph2phen: &#934;313= 0.43 ± 0.03; &#934;365= 0.44 ± 0.02; &#934;404= 0.43 ± 0.02; Clphen: &#934;313= 0.56 ± 0.03; &#934;365= 0.55 ± 0.04; &#404= 0.57 ± 0.06) are independent on the irradiation wavelength indicating only one pathway for the 3ILtrans-bpe excited state population. On the other hand, for fac-[Re(CO)3(NN)(trans-stpy)+ the &#934;true under 404 nm irradiation are lower than those determined for the others irradiation wavelengths (ph2phen: &#934;313= 0.58 ± 0.04; &#934;365= 0.64 ± 0.09; &#934;404 =0.42 ± 0.04; Clphen: &#934;313= 0.54 ± 0.02; &#934;365= 0.58 ± 0.03; &#934;404= 0.42 ± 0.06) which indicate that at higher energies, where the ligand absorbs significantly, there is another pathway that contributes to the 3ILtrans-stpy excited state population. The photoprocess efficiency was evaluated by changing the NN and/or L Iigands, and the differences between the &#934;true can be rationalized mainly in terms of distinct intersystem crossing efficiencies.The photoprocess changes the photophysical properties of these complexes. While the trans isomers exhibit week or no emission at 298 K, the photoproducts, fac-[Re(CO)3(NN)(cis-L)]+, exhibit intense emission driven by 3MLCTRe&#8594;NN excited state, which is sensitive to the medium rigidity. The photochemical reactivity of pentacyanoferrate(II) complexes [Fe(CN)5(NN)]3-, NN = 2-aminobenzilamine (aba), 2-aminobenzamide (ab), 2-(dimethylaminomethyl)-3hydroxypyridine (dmampy), 2-amonomethylpyridine (ampy), 2-aminoethylpyridine (aepy), or 2-(2-methylaminoethyl)pyridine (maepy), were also investigated. Irradiation of these complexes results in the CN- photosubstitution which is detected only when the ligand has an additional coordinating group available near the coordination sphere. The photosubstitution quantum yields are dependent on the irradiation wavelength (&#934;313= 0.13 ± 0.01; &#934;334= 0.091 ± 0.001; &#934;365= 0.056 ± 0.002; &#934;404= 0.022 ± 0.002; &#934;436= 0.015 ± 0.001 for NN = aba), indicating the existence of distinct pathways in which the photoreaction takes place or the distinct population of the reactive excited state due to different intersystem crossing efficiencies. The efficiency of the photoprocess is also dependent on the Iigand (&#955;Irr= 365 nm: &#934;aba= 0.056, &#934;ab= 0.14, &#934;ampy= 0.046, &#934;aepy= 0.066, &#934;maepy= 0.069 e &#934;dmampy= 0.12). For the diamines complexes, the higher quantum yield is observed for [Fe(CN)5(ab)]3-, which exhibit two sites to occur the ring closure. For the aminopiridines, it is óbserved the importance of the chain length on the closure ring efficiency. And that the presence of methyl groups attached to the nitrogen has week or no influence on the photoprocess efficiency.