[1] Tech Univ Darmstadt, Eduard Zintl Inst Inorgan & Phys Chem, D-64287 Darmstadt, Germany
[2] Tech Univ Darmstadt, FB Mat & Geowissensch, D-64287 Darmstadt, Germany
[3] Univ Calif Santa Barbara, Dept Chem & Biochem, Dept Mat, Santa Barbara, CA 93106 USA
[4] Univ Calif Santa Barbara, Mat Res Lab, Santa Barbara, CA 93106 USA
[5] Univ Bonn, Inst Inorgan Chem, D-53121 Bonn, Germany