Different approaches for the theoretical treatment of anions with conventional methods

M. PUIATTI; D. M. A. VERA; A. B. PIERINI

Florianopolis

Congreso; 10 Congreso Latinoamericano de Fisicoquímica Orgánica (CLAFQO10); 2009

h4 { margin-top: 0cm; margin-bottom: 0cm; text-align: center; }h4.western { font-family: "Times New Roman",serif; font-size: 12pt; }h4.cjk { font-family: "DejaVu Sans"; font-size: 10pt; }h4.ctl { font-family: "Lohit Hindi"; font-size: 12pt; }p { margin-bottom: 0.21cm; } DIFFERENT APPROACHES FOR THE THEORETHICAL TREATMENT OF TEMPORARY ANIONS WITH CONVENTIONAL DFT METHODS Marcelo Puiatti, D. Mariano A. Vera, Adriana B. Pierini INFIQC. CONICET. Departamento de Química Orgánica. Fac. de Cs. Químicas. Universidad Nacional de Córdoba. Córdoba. Argentina. E-mail:mpuiatti@fcq.unc.edu.ar The theoretical treatment of molecular anions not a trivial task,[1] especially when dealing with unstable or temporary anions, which have negative electron affinity (EA).[2] According to the nature of their ground state, anions can be classified in two groups: valence (V) and non valence (N), when the unpaired electron is located in a diffuse orbital around the molecule. Conventional methods fail in the treatment of anions when an N anion is found instead of a V one, and the predicted EA is higher than the experimental one, obtained by electron transmission spectroscopy (ETS). In order to solve this situation, new strategies or methodologies for finding the way to get the V states of anions and their EA are presented, explored and evaluated. Recently we presented an alternative method based in the stabilization of the anions exerted by polar solvents.[3] When the N anion is solvated in a polar media ( >1) it became a V anion and the EA could be calculated by extrapolating eq 2, as alternative to the “conventional” eq.1, also using total energies: . Here in we present an evaluation of this method for the calculation of the EA of temporary anions. In addition, we will also explore the possibility for finding the V state as one of the excited states of the N anions, by using the TD-DFT approach. Its actual feasibility in determining very unstable anion state is an open question, which is worth to address, since the stabilization by any means seems to be harder to obtain, the more negative the EA is. TD-DFT would also offer the opportunity of calculating higher vertical EAs apart from the first one, corresponding to the ground anion. These approaches were evaluated by calculating 60 compounds including DNA bases, halogenated, aromatic and cyclic compounds, with different functionals and basis sets. For the first methodology the best results were obtained with the IEFPCM solvent, at the B3LYP/6-311+G(2df,p) level of theory with a correlation with experimental values of EAExp= (1.01 EAcalc+ 0.06) 0.06 eV. For the second alternative the best results were obtained with the PBE0 functional and a correlation ofEAExp= (1.04 EAcalc+ 0.05) 0.21 eV. 1). Simons, J. J. Chem. Phys. A 2008, 112, 6401 and references there in. 2). Vera, D.M.A.; Pierini A.B. Phys. Chem. Chem. Phys.2004, 6, 2833.4. Puiatti, M., D.M.A.; Pierini A.B. Phys. Chem. Chem. Phys.,2008, 10, 1394.