1. Contribution from the Institut des Matériaux Jean Rouxel, 2 rue de la Houssinière, B.P. 32229, 44322 Nantes, Cedex 3, France, Humboldt-Universität, Institut für Chemie, Berlin, D-10117, Germany, National Institute of Chemical Physics and Biophysics, Akadeemia Tee 23, Tallinn, Estonia, Materials Research Laboratory, University of California, Santa Barbara, California 93106, and Physics Department, University of Warwick, Coventry, U.K.