1. Laboratoire de Chimie des Interactions Moléculaires, Collège de France, 11 place Marcelin Berthelot, 75231 Paris Cedex 05, France, Supermolecules Project, JRDC, Kurume Research Center, 2432 Aikawa, Kurume, Fukuoka 839, Japan, Laboratoire de Physique des Solides, Université Paris Sud, bât. 510, 91405 Orsay Cedex, France, and Molecular Device Laboratory, Research Institute for Electronic Science, Hokkaido University, Sapporo 060, Japan