1. Contribution from the Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, Institute of Materials Science, NCSR “Demokritos”, 15310 Ag. Paraskevi, Attiki, Greece, Departamento de Química, C.Q.F.B., Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Quinta da Torre, 2825-114 Caparica, Portugal, and Department of Physics, University of Ioannina, Ioannina, Greece