1. Department of Chemistry, Chungnam National University, Taejon 305-764, Korea, Center for Molecular Science, 373-1 Kusung-dong, Yusung-gu, Taejon 305-701, Korea, Department of Industrial Chemistry, Kyungpook National University, Taegu 702-701, Korea, and Korea Basic Science Institute, 52 Yeoeun-dong, Yusung-gu, Taejon 305-333, Korea