1. Departamento
de Quimica Inorganica, Facultad de Quimica, Pontificia Universidad Catolica de Chile, Casilla 306, Santiago-22, Chile
2. Department
of Chemistry, University of Calgary, 2500 University Drive NW, Calgary, Alberta, Canada T2N 1N4,
3. Organisch-chemisches Institut der Universitat Münster, Corrensstrasse 40, 48149 Münster, Germany