1. Leiden Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands, Department of Chemistry, Warsaw University, Pasteur 1, 02-093 Warsaw, Poland, National Research Council of Canada, 100 Sussex Drive, Ottawa, Ontario K1A 0R6, Canada, and Department of Chemistry, Mount Allison University, Sackville, New Brunswick E4L 1G8, Canada