1. Molecular Sciences Institute, School of Chemistry, University of the Witwatersrand, P. O. Wits, Johannesburg 2050, South Africa, Fax: (internat.) + 27‐11/717‐6749
2. Department of Chemistry and Biochemistry, Ohio University, Athens, OH 75701, United States of America
3. Department of Chemistry, Mississippi College, Clinton, MS 39058, United States of America