1. School of Chemistry and Environmental Science, Xiangnan University, Chenzhou, Hunan, P. R. China;
2. Hunan Provincial Key Laboratory of Xiangnan Rare-Precious Metals Compounds Research and Application, Chenzhou, Hunan, P. R. China
3. College of Chemistry & Pharmacy, Northwest A&F University, Yangling, Shaanxi, P. R. China