Synthesis Of Bis (Nicotinate) Zinc Under Microwave-Assisted Solvothermal Condition

Coordination polymers is one of top topics in the field of materials chemistry due to their applications in a large number of different aspects, such as electrical, optical, magnetic, catalytic and adsorption-desorption. As we known that the structure of coordination polymers determines the characteristic performance, therefore, it is a great challenge for scientific workers to fastly synthesize the coordination polymers for required functionality. Most of zinc complexes have good photoluminescence and nonlinear optical properties, so the study of zinc complexes will have a great significance.At present, hydro(solvo)thermal method is widely used in synthesis of coordination polymers which have high stability. But the conventional hydro(solvo)thermal method requires so much time that it extends the reaction periods. In recent years, microwave technology is widely used in preparing products quickly, so it could overcome this shortcoming. Microwave heating not only shorten the reaction time significantly and improve the yield and purity of product, but also has good reproducibility and stability of the amplification. Therefore, our laboratory use microwave as the heating means. We were succeeded in synthesis of bis(nicotinate)zinc under microwave-assisted solvothermal condition. Also, we obtained bis(nicotinate)zinc which has particle size of about 0.5mm by the combination of microwave-assisted solvothermal method and conventional solvothermal method. The specific descriptions are as follows:We used nicotinic acid as the ligand to coordinate with zinc(Ⅱ) to build the 2D chiral coordination polymer of [Zn(nicotinate)2]n under microwave-assisted solvothermal condition, while dimethylformamide (DMF) was used as the solvent, and the reaction time was only 10min. This method not only shortened the reaction time significantly, but also decreased the temperature of the reaction. The compound were characterized by means of X-ray powder diffraction (XRD), polarized light microscopy, scanning electron microscopy (SEM), fluorescent spectrometry and TG-DTA. The complex has strong fluorescence emission property at room temperature, also the complex has high thermal stability, while TG-DTA showed that the complex has onset decomposition temperature of 400℃.In addition, we also disscussed the influences of reaction time, temperature, solvent, substrate concentration and heating method on the crystallization of the complexes. It was found that the particle size of the crystal would be gradually larger and the shape of the crystal would transit from plate to octahedral when reaction conditions were changed, such as the extension of reaction time, the increase of temperature and substrate concentration. In contrast to conventional solvothermal method, we found that microwave heating can obtain pure [Zn(nicotinate)2]n in 10min, while conventional solvothermal method obtain the mixture of [Zn(nicotinate)2]n and other products. That was noted that microwave heating can not only reduce the reaction time, but also have a better selectivity for the reaction. When we used other solvents, the reaction could not take place under the same reaction conditions, it was noted that DMF was irreplaceable for this reaction.Although microwave-assisted solvothermal method have many advantages, the partical size of crystals obtained from microwave heating was always so small that we couldn't get the structure information of the crystal. So we combined the microwave-assisted solvothermal method and the conventional solvothermal method. Firstly the crystal quickly nucleated under microwave-assisted solvothermal condition; secondly the nucleus got secondary growth under conventional solvothermal condition. The product we obtained not only has the advantages of microwave heating, but also has a larger partical size that suitable for structural analysis. This successful attempt for new synthesis method will have great significance on the synthesis of new compound and the determination of new structure.