1. Department of Chemistry, University of Otago, P. O. Box 56, Dunedin, New Zealand, Fax: +64‐3‐479‐7906
2. Present address: Jiangsu Key laboratory for the Chemistry of Low‐Dimensional Materials, Department of Chemistry, Huaiyin Teachers College, Huai'an 223300, Jiangsu Province, P. R. China
3. School of Chemistry, Monash University, P. O. Box 23, Clayton, Victoria 3800, Australia