1. Department of Inorganic Chemistry, Slovak University of Technology, 81237 Bratislava, Slovakia
2. Department of Inorganic Chemistry, Darmstadt University of Technology, D-64287 Darmstadt, Germany
3. Department of Physical Chemistry, Slovak University of Technology, 81237 Bratislava, Slovakia
4. Laboratoire de Cristallographie et Modelisation des Materiaux Mineraux et Biologiques, CNRS-7036, Universite Henri Poincare - Nancy I, BP 239, F-54506 Vandoeuvre-les-Nancy CEDEX, France