Modelo Sparkle: novos avanÃos para o estudo quÃmico-quÃntico de complexos de lantanÃdeos

AUTOR(ES)

Ricardo Oliveira Freire

DATA DE PUBLICAÇÃO

2007

RESUMO

Since 1994, the Sparkle Model for Lanthanide Complexes has been used for the calculation of ground state geometries of only Eu(III) complexes. In the present thesis, we evolved the Sparkle Model and advanced Sparkle/AM1 and Sparkle/PM3: new paradigms for semiempirical quantum chemical calculations on lanthanide complexes. Parameterizations for all fifteen trivalent lanthanide ions have been carried out in a much more extensive manner, aimed at producing new and models that present results much more accurate. Two aspects of the parameterization procedure used to arrive to these new and enhanced models are important: (i) the choice of a training set capable of representing our universe of 670 lanthanide coordination complexes and (ii) the choice of a response function capable of reproducing geometrical properties, such as bond lengths and bond angles involving the metallic ion. During the parameterization procedure of Sparkle/AM1 for the Eu(III) ion, many tests were carried out and each term of the response function has been exhaustively analyzed until we obtained a really robust parameter set. Similar processes were then used to obtain the parameters for the Sparkle/AM1 and Sparkle/PM3 model parameters for all trivalent lanthanide ions. Our results showed that, both Sparkle/AM1 and Sparkle/PM3 models yielded an unsigned mean error of 0.07Ã for all interatomic distances between the lanthanide ions and the ligand atoms of the first sphere of coordination for the 670 complexes considered, encompassing all trivalent lanthanide ions. For all interatomic distances of the coordination polyhedron (lanthanide â ligand atom and ligand atom â ligand atom) the Sparkle/AM1 and Sparkle/PM3 models present unsigned mean errors of 0.18Ã and 0.15Ã respectively. We also investigated the capabilities of various ab-initio/ECP calculations in reproducing the coordination polyhedron geometries of lanthanide complexes. Our results unexpectedly indicate that RHF/STO-3G/ECP appears to be the most efficient model chemistry in terms of coordination polyhedron crystallographic geometry predictions from isolated lanthanide complex ion calculations. Moreover, both augmenting the basis set and/or including electron correlation generally enlarged the deviations and aggravated the quality of the predicted coordination polyhedron crystallographic geometry. Our results also indicate that the Sparkle/AM1 and Sparkle/PM3 models are of similar or superior accuracy to present day ab-initio/ECP calculations on complexes large enough to be of interest to, for example, luminescence studies, while being hundreds of times faster

ASSUNTO(S)

quÃmica teÃrica espectroscopia de terras raras quÃmica quÃntica quimica complexos de lantanÃdeos

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