1. Department of Chemistry and CSGI, University of Florence, via della Lastruccia 3 Sesto Fiorentino 50019 Florence, Italy, Instituto de Quìmica, Universidade Estadual de Campinas, Caixa Postal 6154, 13083−970 Campinas (Brasil), and Department of Applied Mathematics, Research School of Physical Sciences, Australian National University, Canberra, A. C. T., Australia 0200