Syntheses,Metal Ion Sensing Properties Of Tripodal Multi-Dentate Amide Ligands

Molecular recognition has recently became one of the rising hotspots in supermolecular chemistry. Design of acceptor molecules with multiple recognition sites which is dimensional complementary with metal ions, as well as satisfied with preorganization rules, is the most significant aspect of this researching area. However, researches on Co(II) ion detection are less conducted when compared with those on other metal ion detections. Even fewer studies about colorimetric methods for Co(II) ion detection have been taken. Based on the above-mentioned research background, using the flexible tris2-aminoethyl)amine as an infrastructure, design and synthesis of Tris{2-carbamoyl-(5-rbomethoxy-pyridine-2)ethyl}amine, Tris{2-carbamoyl-(5-carboxy-pyridine-2)ethyl}amine and Tris{2-rbamoyl-(5-nitro-pyridine-2)ethyl} amine were described detailed in this dissertation. Those three different tripodal multi-dentate amine ligands and their cobalt complexes were characterized via X-ray diffraction, IR, MS, NMR. The effects of mutiple subsituents in the ligands on the sensing capability towards Co(II) ion were invested. Specific contents are as follows:1.The synthesis of the ligand I was derived from5-(methoxycarbonyl) picolinic acid as a precursor by chloridization and aminolysis with tris(2-aminoethyl)amine to form the target product We characterized and analyzed the ligand I and its cobalt complexes via X-ray diffraction, IR, MS, NMR. The recognition of ligand I for cobalt ion was studied with UV-vis spectroscopy, the results revealed that the ligand I can sense Co(II) ion selectively, with the detection limit as low as10-5mol·L-1. We also found out the ligand I/Co system was also a sensor for weak acid anions.2. The ligand II was derived from ligand I with a hydrolysis reaction. The Co(II) ion recognition of ligand II was conducted in the Tris-HCl buffer solutions whose pHs were7.2,7.5and7.8, respectively. The recognition of ligand II was studied with UV-vis spectroscopy, while the results showed that the ligand II was not a ideal ligand for Co(II) ion detection since the absorption peak of the complex of Co(II) ion with ligand II was blue shifted compared to that with ligand I, meanwhile, the color change was not that obvious.3.The ligand III was derived from5-nitropyridine-2-carboxyIic acid and tris(2-aminoethyl)amine. The Co(II) ion recognition of ligand II was conducted via UV-vis spectra in which the absorption peak of the complex of Co(II) ion with ligand II was red shifted compared to those with ligand I and ligand II. Since that, we found out that ligand III was a better sensor for Co(II) ion with the detection line reaching106mol/L and a more obvious color change.