1. University of Debrecen, Department of Inorganic and Analytical Chemistry, P. O. Box 21, Egyetem tér 1, Debrecen 4010, Hungary, Fax: +36‐52‐489‐667
2. Present address of the corresponding author: Department of Chemistry, University of Texas at Dallas, P. O. Box 830660, Richardson, Texas 75080, USA, Fax: +1‐972‐883‐2925
3. University of Debrecen, Department of Chemistry, Laboratory for X‐ray Diffraction, P. O. Box 7, Egyetem tér 1, Debrecen 4010, Hungary