2. Materials and experiments
2.1. Materials
chromium (III) nitrate nonahydrate (Cr(NO3)3ยท9H2O) and 1,4-ben-zenedicarboxylic acid (H2BDC) were obtained from J&K (China). N-methylimidazolium and chlorobutanol were purchased from Shanghai Bide Pharmatech Ltd. N,N -dimethylforma-mide (DMF), methanol and ethyl acetate were obtained from Beijing Chemical Works. All chemicals were utilized directly from commercial purchases and without additional purification.