Synthesis And Characterization Of Metallo-supramolecular Gels Of Nitrogen-Rich Ligands

As a new class of polymers, the metallo-supramolecular polymers are not only ahot spot in the field of basic scientific research, but also have potential application intechnology applications due to the integration of advantages of the metal ion andpolymer materials. Especially, particular attention has been paid to themetallo-supramolecular gels discovered in recent years because of their exhibitingdramatic change in response to the application of an environmental stimulus, such astemperature, ionic strength, pH, electric fields, biological and chemical substance, etc.Therefore, they have potential applications as smart films in sensors, actuators,electrooptic devices, catalysis, brake, etc. In this paper2,6-bis(1H-benzimidazolyl)-4-hydroxypyridine was chosen and modified, then ditopic ligands were obtainedwhich is an ideal ligand because of its superior reation ability with metal ions, simpleprocess of synthesis and handling, and easily obtained raw materials. Ultimately, theditopic ligands were used to get reaction with (ZnII) and (LaIII) and themetallo-supramolecular gels were obtained. The structure of the ligands was fullyverified by FT-IR and1H NMR, the dramatic reversible responses of themetallo-supramolecular gels to a variety of stimuli, including thermal, mechanical andchemical were investigated. And the solid-state properties of the gels were alsoexamined by TGA, and WAXDThe main content is as follows:1. Two ditopic ligands,1,4-bis(6-(2,6-bis(benzimidazolyl) pyridyloxy)hexyloxy)benzene(C6’) and1,4-bis(8-(2,6-bis(benzimidazolyl)pyridyloxy)octyloxy)benzene(C8’) were synthesized, consisting of a2,6-bis-(benzimidazolyl)-4-oxypyridinemoiety attached to both end of the ligands. In the presence of a transition metal ion(ZnII) and a lanthanide metal ion (LaIII), we had successfully obtainedmetallo-supramolecular gels. The gels show temperature response in acetonitrile andDMF, in formic acid the gels were destroyed, and became flowable liquid which showthe gels have chemical response. The thermal, optical properties of the polymers wereexamined, Wide angle X-ray diffraction study show that the gels have crystallinestructures. The intensity and shape features of the crystalline depend on the presenceof LaIII, in the presence of the “cross-linking” lanthanum(III) ions, there are more branch in the form of a LaIIInodes, as a consequence, less crystallinity was observed.2. The other two ditopic ligands,1,6-bis-(2,6-bis(benzimidazolyl)pyridyloxy)hexane(C6) and1,8-bis-(2,6-bis(benzimidazolyl)pyridyloxy)octane(C8), alsoconsisting of a2,6-bis-(benzimidazolyl)-4-oxypyridine moiety attached to both end ofthe ligands. In the presence of (ZnII) and (LaIII), also obtainedmetallo-supramolecular gels. The gels show temperature response in acetonitrile andDMF, in formic acid the gels were destroyed, and became flowable liquid which alsoshow the gels have chemical response. The optical and thermal properties of two gelswere similar, their maximum emissions at419nm. Wide angle X-ray diffraction weresimilar with the gels of C6’ and C8’, similarly, the reason could be attributed to thelanthanum. Transition temperature of four gels were examined and compared.3. The monomers named1,4-bis(4-(2,6-bis(benzimidazolyl)pyridyloxy)butoxy)benzene(C4’),1,4-bis-(2,6-bis(benzimidazolyl)pyridyloxy)butane(C4),1,4-bis(3-(2,6-bis(benzimidazolyl)pyridyloxy)propoxy)benzene(C3’) and1,3-bis-(2,6-bis(benzimidazolyl)pyridyloxy)propane (C3) were prepared from1,4-dibromobutane and1,3-di-bromopropane, were homologues of four ligands described above. When takingreaction with (ZnII) and (LaIII), we obtained metallo-supramolecular gels of C4’ andC4, however, this phenomenon did not observed on C3’ and C3, which show that itwas not good for forming a gel with the decrease of carbon atoms in the ligand’s mainchain. Comparing to ligands that could form gels, there were all ditopic. In order todiscuss this particularity, the monomer,2,6-bis (1H-benzimidazolyl)-4-hexylox--ypyridine(C6’’) was prepared from1-bromohexane and2,6-bis(1H-benzimidazolyl)-4-hydroxypyridine, in the presence of ZnIIand LaIII, no gel obtained, which show thatit was necessary for the ligand being ditopic.