新型Cd-苯并噻二唑类的金属有机骨架中的光诱导脱羧反应

基于相同配体2,1,3-苯并噻二唑-4,7-二羧酸(H2BTDC),通过不同的溶剂热反应,合成了两个新的3D结构的金属有机框架配合物1Cd_4(BTDC)_4·5H_2O]和2Cd_2(BTDC)_2(DMF)·1.5H_2O]。在配合物1的结构中存在两个相邻发色团(BTD单元)为反式平行的排列方式,距离为3.987,小于反式二聚物的理论计算值(4 ?)。在相关的紫外可见吸收光谱中观察到,配合物1在470nm处吸收带的能量低于单个BTD单元典型吸收带的能量。这些证据揭示了在配合物1的结构中存在反式苯并噻二唑二聚体。通过研究光照前后配合物1和2的稳态光谱及电子顺磁共振(EPR)光谱发现,这两个配合物中存在光诱导电子转移引起的光致变色效应,并产生了相应的阴离子自由基。相关的FT-IR光谱表明,由于这一自由基的产生,配合物1和2进一步发生了配体单元的脱羧反应,释放出二氧化碳气体(2331cm~(-1)、2361cm~(-1))。

Photoinduced Decarboxylation Reaction in New Cd-benzothiadiazole Metal-organic Framework

Based on the same benzothiadiazole (BTD) ligand (H2L =2,1,3-benzothiadiazole-4,7-dicarboxylic acid),two new 3D BTD-derived Cd (Ⅱ) metal-organic frameworks 1 Cd4 (BTDC)4 · 5H2O] and 2 Cd2 (BTDC)2 (DMF) · 1.5H2O] were obtained by the different solvothermal reactions.Interestingly,in 1,partial BTD units arranged in an anti-parallel mode,and the distance between these BTD units was 3.987 (A),which was less than that valued by theoretical calculation (4 (A)).Furthermore,evidencedby UV-Vis solid state absorption spectra of 1,the energy of absorption band at 470 nm was lower than those from typical monomerBTD unit.Hence,the structural analysis and photophysical study distinctly demonstrated the evidence of BTD anti-dimmerin 1.More importantly,the UV and fluorescence spectra after illumination showed that there were interesting photochromic phenomena in both complexes 1 and 2 triggered by photoinduced electron transfer,where anionic radical was also directly observed by the electron paramagnetic resonance (EPR) spectra before and after the illumination.Herein,FT-IR spectra show that the subsequent decarboxylation of ligand unit results to release CO2 gas (2331 cm-1,2361 cm-1) in complexes 1 and 2.