1. Department of Chemistry, Korea University, 208 Seochang, Chochiwon, Chung-nam 339-700, Korea, Organometallic Chemistry Laboratory, Korea Institute of Science and Technology, P.O. Box 131, Cheongryangri, Seoul 130-650, Korea, Department of Chemical Technology, Taejon National University of Technology, Taejon 300-717, Korea, and Department of Material Science, Korea University, Seoul, Korea