1. School of Engineering and Science, International University Bremen, P.O. Box 750 561, 28725 Bremen, Germany, Department of Chemistry and Biochemistry, Florida State University and National High Magnetic Field Laboratory and Center for Interdisciplinary Magnetic Resonance, Tallahassee, Florida 32306-4390, and Laboratoire de Physico-Chimie de la Matière Condensée, Université Montpellier II, case courrier 003, 34095 Montpellier Cedex 5, France