Estudio teórico de la dimerización entre iones radicales en cristales moleculares de interés tecnológico

Resumen

The objective of this PhD Thesis is the study of the dimerization process in the organic radical ions: TCNE·- (Anion Tetracyanoethylene), TCNQ·- (Anion 7,7,8,8-tetracyano-quinodimethane), Q·- (Anion cyanil or 1,2,4,5-tetracyano-quinone), TTF·+ (Tetrathiafulvalene) and TMPD·+ (N,N,N',N'-tetramethyl-p-phenylenediamine). They were taken as prototypes of anion and cation radicals. The aim of the study of the dimerization is: (a) the importance or the process per se, as it is an interaction between radicals that present charge of the same sign,; (b) The five ion radicals selected are typical building-blocks in molecular magnetic and conducting materials, and the presence of dimers is known to affect the presence of the magnetic and conducting properties. There are other organic radical species able to form diamagnetic dimers (anions, cations and neutral molecules) but we have decided to study this set indicated above due to its reasonable size and relevance as building-blocks. For the study of the interaction that gives raise to the formation of the dimers we have used some of the most common methods of the Computational Chemistry: (a) The Density Functional Theory (DFT) using the B3LYP functional in the Restricted and Unrestricted forms as implemented in the GAUSSIAN package. (b) The Perturbation Theory applied to Multireferent wavefunctions, using the MCQDPT2 method implemented by Nakano and Hirao in the GAMESS package. (c) Specifically, other methods like the Complete Active Space method (CASSCF), the Hartree-Fock theory (HF) or the Møller-Plesset 2nd Order Perturbation Theory (MP2). We used the 6-31+G(d) basis set and the LanL2dz or 3-21G in cases where 6-31+G(d) is not applicable. The Base Superposition Error (BSSE) was calculated by the Counterpoise Method. We also used the Cambridge Structural Database (CSD) to search of crystalline structures and the AIMPAC package for the Bader analysis of the electronic density.