1. Institute of Inorganic and Analytical Chemistry Justus Liebig University Giessen Heinrich-Buff-Ring 17 35392 Giessen Germany
2. Department of Chemistry and Pharmacy Friedrich Alexander University Erlangen-Nürnberg Egerlandstraße 1 91058 Erlangen Germany
3. Fraunhofer Institute for Silicate Research Neunerplatz 2 97082 Würzburg Germany
4. Center for Materials Research Heinrich-Buff-Ring 16 35392 Giessen Germany