* Corresponding authors

^a State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, 5625 Renmin Street, Changchun 130022, China
E-mail: fengj@ciac.ac.cn, hongjie@ciac.ac.cn
Fax: +86 431 85698041
Tel: +86 431 85262127

^b University of Science and Technology of China, Hefei 230026, China

^c Department of Chemistry, Tsinghua University, Beijing 100084, China