1. Contribution from the Debye Institute, Department of Inorganic Chemistry and Catalysis, Utrecht University, Sorbonnelaan 16, 3508 TB Utrecht, The Netherlands, Department of Organic Chemistry and Catalysis, Delft University of Technology, Julianalaan 136, 2628 BL, Delft, The Netherlands, and Department of Physical Chemistry/Solid-State NMR, NSR Center, University of Nijmegen, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands