1. Department of Chemistry and Bioscience, Kemigården 3, Chalmers University of Technology, SE- 412 96 Göteborg, Sweden, Departament de Química Física, Universitat de València, Dr. Moliner 50, E-46100 Burjassot, Spain, and Department of Chemistry, Organic Chemistry, Uppsala University, Box 599, SE−751 24 Uppsala, Sweden