1. Department of Chemistry, Martin-Luther University Halle-Wittenberg, Institute of Organic Chemistry, Kurt-Mothes Strasse 2, D-06120 Halle, Institute of Physical Chemistry, Mühlpforte 1, D-06108 Halle, and Department of Chemistry TU Chemnitz, Institute of Inorganic Chemistry, Strasse der Nationen 62, D-09111 Chemnitz, Germany