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Master's Dissertation
DOI
10.11606/D.76.1995.tde-08122010-093039
Document
Author
Full name
Claudia Elisabeth Munte
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Carlos, 1995
Supervisor
Committee
Nascimento, Otaciro Rangel (President)
Panepucci, Horacio Carlos
Walmsley, Lygia Christina de Moura
Title in Portuguese
Estrutura molecular e espectros de EPR do composto monocristalino CuBr2(fdmp)2.
Keywords in Portuguese
Estrutura molecular
Monocristal
RPE
Abstract in Portuguese
Estão sendo apresentados, neste trabalho, estudos estruturais e magnéticos do composto de [CuBr2(fdmp)2] utilizando as técnicas de difração de Raio-X e espectroscopia de EPR. a complexo cristaliza no grupo espacial P21/n com a=8.1653(47)Å, b=10.432(3)Å, c=13.385(4)Å, β=100.12(4)° e Z=2. Os íons de Cu(II), que estão em coordenação quadrado-planar trans ligando-se a dois Nitrogênios e dois Bromos, se encontram em centros de inversão. Somente urna linha de EPR e observada, proveniente do colapso das ressonâncias relativas aos dois íons de Cu(II) magneticamente não equivalentes, causado pela interação de troca. Devido a diferença significativa entre os pesos atômicos do Nitrogênio e Bromo, não e esperada urna simetria axial para o tensor g como é comum ocorrer em vários complexos de Cu(II); de fato, a decomposição de g cristalino para os dois g moleculares revela três autovalores distintos. Alem disso, a direção de maior g não coincide exatamente com a normal ao quadrado-planar, como é comum nesses complexos: se encontra rodada de ∼ 5° em direção ao Bromo, caracterizando um estado fundamental do tipo dx2-y2 com mistura de dyz. Outro fato incomum verificado foi a dependência do fator g com a freqüência e a presença de contribuições não-seculares, característicos de sistemas em que a freqüência de troca é próxima a freqüência de Larmor. Uma analise da variação angular da largura de linha de ressonância foi utilizada para a determinação do parâmetro de troca ‌J‌. Está também incluído, neste trabalho, um método numérico de decomposição de g cristalino em g moleculares e sua comparação com métodos da literatura.
Title in English
Molecular structure and EPR spectra of the monocrystalline compound CuBr2(fdmp)2.
Keywords in English
EPR
Molecular structure
Monocrystal
Abstract in English
In the present work, we discuss the structural and magnetic properties of the [CuBr2(fdmp)2] compound deduced from studies of X-ray diffraction and EPR spectroscopy. This complex crystallizes in the spatial group P21/n with a=8.1653(47)Å, b=10.432(3)Å, c=13.385(4)Å, β=100.12(4)° and Z=2. The copper ions, Cu (II), are in a square-planar coordination bound to two nitrogen and two bromine atoms. They are localized in inversion centers. Only one EPR line has been observed due to the collapse of the resonances of the two magnetically inequivalent Cu (II) ions caused by a strong exchange interaction between them. Since nitrogen and bromine have significantly different atomic weights we may not expect an axially symmetric g-tensor as is commonly found in many Cu (II) complexes. In fact, the decomposition of the experimental crystalline g-tensor into two molecular tensors reveals three distinct eigen-values. Furthermore, the axis of the largest molecular eigen-value does not exactly coincide with the normal of the square plane: it is rotated by ∼ 5° toward the bromine atom which characterizes a dx2-y2 ground state with some contribution from a dyz state. Another unusual fact that has been revealed in our studies is the frequency dependence of the g-factor, due to the presence of non-secular contributions to Hamiltonian, which are characteristic for systems with a exchange frequency near the Larmor frequency. In order to determine the exchange factor ‌J‌, we analyzed the angular dependence of the line broadening. In the present work we also included a numerical method for the decomposition of the crystalline g-tensor into molecular ones and compared it with other methods found in the literature.
 
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Publishing Date
2010-12-10
 
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