1. Department of Chemistry, University of Siena, Via A. Moro, 53100 Siena, Italy
2. Department of Chemistry, University of Florence, Via della Lastruccia 3, I-50019 Sesto Fiorentino, Italy
3. Faculty of Chemistry, University of Wroclaw, F. Joliot-Curie 14, 50-383 Wrocław, Poland