1. Departamento de Quimica, Cinvestav, Avenida IPN # 2508 Col. San Pedro Zacatenco, C. P. 07360, Mexico, D.F., Mexico, Department of Chemistry, Structure Determination Laboratory, University of Alberta, Edmonton, Alberta T6G 2G2, Canada, and Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada