Desenvolvimento de um novo complexo macrocíclico do sistema cobalto cyclam
In this work were synthesized and studied the spectroscopic and electrochemical characteristics of the coordination compounds trans-[Co (cyclam)Cl2]Cl, trans- Na[Co(cyclam)(tios)2], trans-[Co(en)2Cl2]Cl and trans-Na[Co(en)2(tios)2], where tios = thiosulfate and en = ethylenediamine. The compounds we...
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| Formato: | Dissertação |
| Idioma: | por |
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Universidade Federal do Rio Grande do Norte
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| Endereço do item: | https://repositorio.ufrn.br/jspui/handle/123456789/17650 |
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| Resumo: | In this work were synthesized and studied the spectroscopic and electrochemical
characteristics of the coordination compounds trans-[Co (cyclam)Cl2]Cl, trans-
Na[Co(cyclam)(tios)2], trans-[Co(en)2Cl2]Cl and trans-Na[Co(en)2(tios)2], where tios =
thiosulfate and en = ethylenediamine. The compounds were characterized by: Elemental
Analysis (CHN), Absorption Spectroscopy in the Infrared (IR), Uv-Visible Absorption
Spectroscopy, Luminescence Spectroscopy and Electrochemistry (cyclic voltammetry).
Elemental Analysis (CHN) suggests the following structures for the complex: trans-
[Co(cyclam)Cl2]Cl.6H2O and trans-Na[Co(cyclam)(tios)2].7H2O. The electrochemical
analysis, when compared the cathodic potential (Ec) processes of the complexes trans-
[Co(cyclam)Cl2]Cl and trans-[Co(en)2Cl2]Cl, indicated a more negative value (-655
mV) for the second complex, suggesting a greater electron donation to the metal center
in this complex which can be attributed to a greater proximity of the nitrogen atoms of
ethylenediamine in relation to metal-nitrogen cyclam. Due to the effect of setting
macrocyclic ring to the metal center, the metal-nitrogen bound in the cyclam are not as
close as the ethylenediamine, this fact became these two ligands different. Similar
behavior is also observed for complexes in which the chlorides are replaced by
thiosulfate ligand, trans-Na[Co(en)2(tios)2] (-640 mV) and trans-Na[Co(cyclam)(tios)2]
(-376 mV). In absorption spectroscopy in the UV-visible, there is the band of charge
transfer LMCT (ligand p d* the metal) in the trans-Na[Co(cyclam)(tios)2] (350
nm, p tios  d* Co3+) and in the trans-Na[Co(en)2(tios)2] (333 nm, p tios d*
Co3+), that present higher wavelength compared to complex precursor trans-
[Co(cyclam)Cl2]Cl (318 nm, pCl  d* Co3+), indicating a facility of electron density
transfer for the metal in the complex with the thiosulfate ligand. The infrared analysis
showed the coordination of the thiosulfate ligand to the metal by bands in the region
(620-635 cm-1), features that prove the monodentate coordination via the sulfur atom.
The νN-H bands of the complexes with ethylenediamine are (3283 and 3267 cm-1) and
the complex with cyclam bands are (3213 and 3133 cm-1). The luminescence spectrum
of the trans-Na[Co(cyclam)(tios)2] present charge transfer band at 397 nm and bands dd
at 438, 450, 467, 481 and 492 nm. |
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