1. Facultad de Química, Universidad Nacional Autónoma de México. Ciudad Universitaria, C.P. 04510 México D.F., México
2. Department of Chemistry, Brooklyn College of the City University of New York, 2900 Bedford Ave., Brooklyn, NY 11210, USA
3. Department of Chemistry, Graduate Center of the City University of New York, 365 Fifth Ave., New York, NY 10016, USA