1. Key Laboratory of Synthetic and Natural Functional Molecule of the Ministry of Education College of Chemistry and Materials Science Northwest University Xi'an 710069 P. R. China
2. Key Laboratory of Magnetic Molecules and Magnetic Information Materials (Ministry of Education) School of Chemistry and Material Science Shanxi Normal University Taiyuan 030006 P. R. China
3. School of Chemistry and Chemical Engineering Xi'an University of Architecture and Technology Xi'an 710055 P. R. China