Modelagem estrutural em solução por métodos contínuos de solvatação

Abstract

In the first part of this work, several schemes for PCM method (Polarizable Continuum Model) calculations were employed within the Gaussian Program, with the purpose of suggesting more suitable and rational calculation protocols designed for organic systems involving the gauche effect. For this, the 1,2-dihaloethanes (DHEs) series (H2XC 􀀀 CXH2, where X = F, Cl, Br and I) were chosen as model systems as long as they are classical systems with well established experimental characterization of the gauche effect. Then, free energy solvation energies for the gauche and anti forms were theoretically determined in different solvents, two non polar (cyclohexane and CCl3), one weakly polar (CHCl4) and one very polar (DMSO). Several cavity models were tested. Two versions of the Gaussian Program, namely 2003 and 2009, and DFT-type quantum chemical methods (B3LYP and M05-2X) were employed with the following basis sets: 6-31g*, 6-31+g*, 6-311g*, 6-311+g*, cc-PVTZ and def2-TZV. The results have shown that the electrostatic portion of the solvation is dominant over the nonelectrostatic component, and furthermore the former defines alone the qualitative trend concerning the relative energies among the conformers. Yet, it was observed that the Pauling and Bondi radii models used for the cavity’s building were the most appropriate. Also, for the F, Cl and Br elements, the 6-31+g*, 6-311g* and 6-311+g* basis sets yielded better results. For iodine, it were used the LanL2DZ, CRENBL and SttutRLC pseudopotentials. The LanLD2Z one gave better results. In the second part of this work, aqua-complexes of trivalent lanthanide (Ln3+) ions in gas and water solution phases were studied, for the whole Ln series. After optimizing the geometries of the complexes in vacuum (isolated), calculations without structural relaxation were done in solution, using the cosmo continuum solvation model. The thermodynamics of the reaction [Ln(H2O)9]3+(aq) ! [Ln(H2O)8]3+(aq) + H2O was analysed. Up to moment, only semiempirical results, using the Sparkle model (AM1 and PM3) within the MOPAC Program, were obtained. DFT results are in progress.