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Previous issue date: 2016-07-29 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES) / No presente trabalho ? descrito a s?ntese e a caracteriza??o dos compostos de
coordena??o entre os nitratos de lantan?deos (III) e a pirazinacarboxamida (PyZ), visando uma
poss?vel aplica??o funcional desses novos compostos como dispositivos moleculares
conversores de luz. Os complexos obtidos foram caracterizados por meio de diversas t?cnicas
anal?ticas, das quais podemos destacar: an?lise elementar, condutividade eletrol?tica molar,
termogravimetria (TG) e an?lise t?rmica diferencial (DTA) simult?nea, calorimetria
explorat?ria diferencial (DSC), espectroscopia de absor??o no infravermelho m?dio (FT-IR),
espectroscopia por energia dispersiva de raios-X (EDS), difratometria de raios-X (DRX) pelo
m?todo do p?, espectroscopia de absor??o eletr?nica (UV-Vis) a 298 K e espectroscopia de
luminesc?ncia a 298 K. Atrav?s dos resultados de an?lise elementar, termogravimetria e de
condutividade eletrol?tica molar, foi poss?vel propor as seguintes f?rmulas moleculares:
[Ln(PyZ)2(NO3)2]NO3.2H2O (Ln3+ = La?Eu) e [Ln(PyZ)2(NO3)2]NO3.H2O (Ln3+ = Gd?Dy).
As curvas TG-DTA e DSC forneceram informa??es a respeito da desidrata??o, degrada??o,
estabilidade e natureza dos eventos t?rmicos referentes aos processos de decomposi??o. Os
dados de condutividade, tanto em nitrometano como em acetonitrila, sugeriram
comportamento de eletr?lito 1:1 para todos os compostos, refor?ando os resultados dos
espectros de absor??o na regi?o do infravermelho m?dio, que indicaram a presen?a de nitrato
n?o coordenado aos ?ons met?licos. Nos espectros eletr?nicos no UV-Vis observou-se o
deslocamento das bandas de absor??o dos complexos estudados, quando comparadas ?s
bandas do ligante livre, sugerindo a coordena??o do ?on met?lico central com o ligante
pirazinacarboxamida. A an?lise dos espectros de absor??o na regi?o do infravermelho (FT-IR)
permitiram estabelecer que os s?tios de coordena??o do ligante PyZ com o ?on met?lico s?o o
oxig?nio carbon?lico e o nitrog?nio ? do anel piraz?nico. A interpreta??o dos difratogramas de
raios-X revelou a exist?ncia de tr?s s?ries isom?rficas: a primeira compreende os compostos
de La3+ e Ce3+, a segunda os compostos de Pr3+ ao Tb3+ e a terceira ao composto de Dy3+. O
estudo das bandas hipersensitivas do complexo de neod?mio no estado s?lido a 298 K
permitiu determinar os par?metros espectrosc?picos, cujos valores num?ricos indicam que a
intera??o metal-ligante ? essencialmente eletrost?tica. A partir dos espectros eletr?nicos
obtidos em solu??o de acetonitrila e etanol calculou-se a for?a do oscilador (P), cujos valores
sugerem uma maior influ?ncia do etanol na esfera de coordena??o do ?on Nd3+. O espectro de
emiss?o do complexo de gadol?nio revelou que a energia do estado tripleto excitado do ligante PyZ, encontra-se acima dos n?veis emissores dos ?ons Eu e Tb, o que favorece o processo de
transfer?ncia de energia metal-ligante. Baseando-se na an?lise do espectro de emiss?o do
composto de eur?pio no estado s?lido a 298 K, foi poss?vel atribuir uma microssimetria
aproximadamente D2d, consistente com a geometria de um dodecaedro distorcido para o
composto. A an?lise de luminesc?ncia sugere que os complexos de Eu3+, Tb3+, Sm3+ e Dy3+
apresentam emiss?es caracter?sticas na regi?o dos ?ons lantan?deos, por?m, quando em
solu??o de acetonitrila, apenas o complexo de sam?rio n?o apresentou emiss?o na regi?o do
vis?vel por ter possivelmente sua luminesc?ncia suprimida pela presen?a do solvente. / This present work describes the synthesis and characterization of coordination
compounds between lanthanide nitrate (III) and pyrazinecarboxamide (PyZ), intending a
possible functional application of these new compounds as molecular light conversion
devices. The obtained compounds were characterized by various analytical techniques, of
which we highlight: elemental analysis, molar electrolytic conductivity, thermogravimetry
(TG) and differential thermal analysis (DTA) simultaneous, differential scanning calorimetry
(DSC), absorption spectroscopy in mid infrared (FT-IR) spectroscopy by energy dispersive Xray
(EDS), diffraction X-ray (XRD) by the powder method spectroscopy electronic absorption
(UV-Vis) at 298 K and luminescence spectroscopy at 298 K. From the results of elemental
analysis, thermogravimetry and molar electrolytic conductivity, it was possible to propose the
following molecular formulas: [Ln(PyZ)2(NO3)2]NO3.2H2O (Ln3+ = La-Eu) and [Ln(PyZ)2
(NO3)2]NO3.H2O (Ln3+ = Gd-Dy). The TG-DTA and DSC curves provided information about
dehydration, degradation, stability and nature of thermal events related to decomposition
processes. The conductivity data, both nitromethane and acetonitrile, suggested an electrolyte
behavior 1:1 for all compounds, reinforcing the results of the absorption spectra in the middle
infrared region, which indicated the presence of nitrate is not coordinated to the metal ions.
Regarding the electronic spectra UV-Vis, it was observed displacement of the absorption
bands of the studied complexes, when compared to the free ligand bands, suggesting the
coordination of the central metal ion with the binder pyrazinecarboxamide. The analysis of
absorption spectra in the infrared (FT-IR) leads to stabilish that sites of coordination with the
PyZ binder metal ion are carbonyl oxygen and nitrogen ? pyrazine ring. The interpretation of
X-ray diffraction revealed the existence of three isomorphic series: the first comprises those
compounds of La3+ and Ce3+, the second compounds of the Pr3+, Tb3+ and Dy3+ to the third
compound. The study of hipersensitivas bands of neodymium complex in the solid state at
298 K allowed the determination of spectroscopic parameters, numerical values which
indicate that metal-ligand interaction is essentially electrostatic. The oscillator strength (P)
was calculated from the electronic spectra in acetonitrile solution and ethanol. The P values
suggest a greater influence of ethanol in coordination ion Nd3+ ball. The emission spectrum of
the gadolinium complex showed that the energy of the excited triplet state PyZ binder is
between the emitting level of the Tb ions and I, which favors the process of metal-ligand
energy transfer. Based on the analysis of the europium compound emission spectrum in the solid state at 298 K, it was possible to assign a microssimetria approximately D2d, consistent
with the geometry of a distorted dodecahedron for the compound. Luminescence analysis
suggests that the complexes of Eu3+, Tb3+, Sm3+ and Dy3+ display characteristic emissions in
the region of lanthanide ions, however, when in acetonitrile solution, only samarium complex
showed no emission in the visible region, probaly because a suppression of luminescence by
the presence of the solvent.
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.ufrn.br:123456789/22210 |
| Date | 29 July 2016 |
| Creators | Carvalho, Genickson Borges de |
| Contributors | 31482015404, http://lattes.cnpq.br/2959800336802498, Oliveira, Otom Anselmo de, 03936872449, http://lattes.cnpq.br/7903084274135177, Borges, Filipe Martel de Magalh?es, 83724427468, http://lattes.cnpq.br/3125652251177322, Santos, Klecia Morais dos, 00836353439, http://lattes.cnpq.br/7924455214362992, Martins, Daniel Freitas Freire, 05305550424, http://lattes.cnpq.br/1834691679987332, Leite, Cleide Maria da Silva, 39123847387, http://lattes.cnpq.br/9540139741183164, Silva, Ademir Oliveira da, Moura, Maria de F?tima Vit?ria de |
| Publisher | PROGRAMA DE P?S-GRADUA??O EM QU?MICA, UFRN, Brasil |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/doctoralThesis |
| Source | reponame:Repositório Institucional da UFRN, instname:Universidade Federal do Rio Grande do Norte, instacron:UFRN |
| Rights | info:eu-repo/semantics/openAccess |
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