1. Kekulé-Institute of Organic Chemistry and BiochemistryUniversity of Bonn Gerhard-Domagk Strasse 1 53121 Bonn Germany
2. current address: Arlanxeo Netherlands B.V. Urmonderbaan 24 6167 RD Geleen The Netherlands
3. Mulliken Center for Theoretical ChemistryUniversity of Bonn Beringstrasse 4 53115 Bonn Germany
4. Department of ChemistryUniversity of Jyväskylä P.O. Box 35 40014 Jyväskylä Finland
5. current address: Department of ChemistryMcGill University 801 Sherbrooke St. West Montreal Qc H3A 0B8 Canada
6. Institute of Inorganic ChemistryUniversity of Bonn Gerhard-Domagk Strasse 1 53121 Bonn Germany