1. Department of Chemistry, Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan, Department of Chemistry, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo 152-8551, Japan, and Laboratoire Louis Néel, CNRS, BP 166, 25 Avenue des Martyrs, 38042 Grenoble Cedex 9, France