1. Dipartimento di Chimica, Università di Perugia, I-06100 Perugia, Italy
2. Institut de Chimie Minérale et Analytique, BCH, Université de Lausanne, CH-1015 Lausanne, Switzerland
3. Department of Chemistry, Faculty of Science, Kyushu University, Hakozaki, Fukuoka 812, Japan
4. Department of Chemistry, Faculty of Science, Kumamoto University, Kurokami 2-39-1, Kumamoto 860, Japan