1. Contribution from the Department of Chemistry, Faculty of Sciences, Vrije Universiteit, De Boelelaan 1083, NL-1081 HV, Amsterdam, The Netherlands, Leiden Institute of Chemistry, Gorlaeus Laboratoria, University of Leiden, P.O. Box 9502, NL-2300 RA, Leiden, The Netherlands, and Department of Chemistry, University of Basilicata, Via N. Sauro 85, 85100 Potenza, Italy