1. Universiteit van Amsterdam, van't Hoff Institute for Molecular Sciences, Laboratory for Crystallography, Nieuwe Achtergracht 166, NL-1018WV Amsterdam, The Netherlands, University of Nijmegen, Physical Chemistry/Solid State NMR, NSRIM Center, Toernooiveld 1, NL-6525 ED Nijmegen, The Netherlands, and DSM Research, Postbus 18, 6160 MD, Geleen, The Netherlands