1. Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, P. O. Box 9502, 2300 RA Leiden, The Netherlands, Fax: (internat.) + 31‐71/527‐4671
2. Institute of Applied Synthetic Chemistry, Vienna University of Technology, Getreidemarkt 9/163‐AC, 1060 Vienna, Austria
3. Institute of Molecular Chemistry, Laboratory of Crystallography, Universiteit van Amsterdam, Nieuwe Achtergracht 166, 1018WV Amsterdam, The Netherlands
4. Institute of Solid State Physics, Vienna University of Technology, Hauptstrasse 8‐10/131, 1040 Vienna, Austria