摘要
In order to explore the effect mechanism of solvent on the synthesis of the metal organic framework materials, the microscopic interaction between solvent and framework and the effects of N,N-dimethyl-formamide(DMF) or N-methyl- 2-pyrrolidone(NMP) on solvothermal synthesis of [Zn4O(BDC)3]8 were investigated through a combined DFT and experimental study. XRD and SEM showed that the absorbability of NMP in the pore of [Zn4O(BDC)3]8 was weaker than that of DMF. The thermal decomposition temperature of [Zn4O(BDC)3]8 synthesized in DMF was higher than that in NMP according to TG and FT-IR. In addition, the nitrogen sorption isotherms indicated that NMP improved gas sorption property of [Zn4O(BDC)3]8. The COSMO optimized calculations indicated that the total energy of Zn4O(BDC)3 in NMP was higher than that in DMF, and compared with non-solvent system, the charge of zinc atoms decreased and the charge value was the smallest in NMP. Furthermore, the interaction of DMF, NMP or DEF in [Zn4O(BDC)3]8 crystal model was calculated by DFT method. The results suggested that NMP should be easier to be removed from pore of materials than DMF from the point of view of energy state. It can be concluded that NMP was a favorable solvent to synthesize [Zn4O(BDC)3]8 and the microscopic mechanism was that the binding force between Zn4O(BDC)3 and NMP molecule was weaker than DMF.
为探究溶剂对合成有机金属框架化合物的影响机制,采用实验和DFT理论计算相结合的方法,研究溶剂N,N-二甲基甲酰胺(DMF)和N-甲基-2-吡咯烷酮(NMP)对溶剂热法合成有机金属框架材料[Zn4O(BDC)3]8的影响及溶剂与框架间的微观作用机制。粉末X射线衍射(XRD)和扫描电镜(SEM)结果表明,NMP在[Zn4O(BDC)3]8孔道中的吸附力较DMF的弱,NMP分子更容易从框架中脱除;热重(TG)和热重-红外联用(TGA/FT-IR)结果表明,以DMF为溶剂合成的[Zn4O(BDC)3]8的热分解温度和热稳定性较高;氮气等温吸附实验(BET)发现,以NMP为溶剂合成的[Zn4O(BDC)3]8的气体吸附性能更强,兰缪尔比表面积高于用DMF合成的[Zn4O(BDC)3]8。调控介电常数设定溶剂分别为NMP和DMF,用COSMO溶剂化方法对溶剂分子与框架化合物基本结构单元Zn4O(BDC)3间相互作用模型进行几何优化计算,发现溶剂设定为NMP时Zn4O(BDC)3优化结构的总能量较溶剂设定为DMF时的高8.6405 k J/mol,这说明DMF分子与Zn4O(BDC)3间的结合力强于NMP分子的,溶剂化作用降低了Zn与O间的离子性;用DMol3在GGA-BLYP/DN水平计算了DMF、NMP或DEF溶剂分子在[Zn4O(BDC)3]8晶体孔道中的相互作用,与DMF相比,NMP在孔道中能量状态稳定性较差,在能量状态角度上NMP应最容易从框架材料孔道中脱除。研究结果说明NMP更有利于合成性质良好的[Zn4O(BDC)3]8,与DMF相比NMP与框架结构基元间的作用力较弱。
基金
Project(51104185)supported by the National Natural Science Foundation of China
Project(2010QZZD003)supported by the Key Project of Central South University of Fundamental Research Funds for the Central Universities of China
