1. Contribution from the Department of Chemistry, Faculty of Science, Kyushu University, Hakozaki, Higashi-ku, Fukuoka 812, Japan, Dipartimento di Chimica, Università di Perugia, I-06100 Perugia, Italy, and Institut de Chimie Minérale et Analytique, BCH, Université de Lausanne, CH-1015 Lausanne, Switzerland