1. Max-Planck-Institute for Solid State Research, Heisenbergstrasse 1, D-70569 Stuttgart, Germany, Laboratory of Crystallography, University of Bayreuth, D-95440 Bayreuth, Germany, Institute for Inorganic and Applied Chemistry, University of Hamburg, Germany, and 2 MAX-lab, Inorganic Chemistry, Lund University, P.O. Box 124, SE-22100 Lund, Sweden