1. Organic Solid Laboratory, BNLMS & CMS, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China
2. Laboratoire de Chimie de Coordination Organique, CNRS-UMR7140, Université de Strasbourg, 4 rue Blaise Pascal, 67000 Strasbourg Cedex 1, France
3. Department of Organic and Polymeric Materials, Graduate School of Science and Engineering, Tokyo Institute of Technology, O-Okayama, Tokyo 152-8552, Japan
4. Department of Physics, Peking University, Beijing 100871, P. R. China
5. Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, U.K.