1. Department of Chemistry and CAMDRC, Soongsil University, 1-1 Sangdo-Dong, Dongjak-Gu, Seoul 156-743, Korea, Department of Chemistry, Kwangwoon University, 447-Wolgye-Dong, Nowon-Gu, Seoul 139-701, Korea, and Department of Chemistry and Biochemistry, Oberlin College, Oberlin, Ohio 44074-1097