1. Contribution from the Facultad de Química, Universidad de Guanajuato. Col. Noria Alta s/n C.P. 36050, Guanajuato, Gto., México, Physikalische Chemie, Fachbereich Chemie, TU Dresden, D-01062 Dresden, Germany, Center for Computational Chemistry, University of Georgia, Athens, Georgia 30602-2525