Metal Ion-induced Formation Of Small Organic Molecules Studied Supramolecular Metal Gels

Supramolecular gels is a class of substance through non-covalent bonding between smallmolecules by self-assembly to form a network structure binding the solvent. It has developed intoa class of intelligent/functional nanomaterials with broad application prospects. In recent years, alot of small molecular gels （LMOGs） and their application have been reported, but reports onsupramolecular （non-polymeric） metal gels rarely. Amide derivatives with the group of pyridineoften were used as gelator to gel test, as its N of pyridine group, the NH of amide group and thecarbonyl can easily form intramolecular and intermolecular hydrogen bonds.In this paper, with anhydrous DMF as catalyst and anhydrous THF as solvent, N,N′,N″-tris（3-pyridyl）trimesic amide（L1）、N,N′,N″-tris（4-pyridyl）trimesic amide（L2）、N,N′-bis（3-pyridyl）terephthalamide（L3） and N,N′-bis（4-pyridyl）terephthalamide（L4） were synthesized from1,3,5-benzenetricarboxylic acid,1,4-benzenedicarboxylic acid, thionyl chloride,3-aminopyridine and4-aminopyridine by controlling the reaction conditions. We explored if they can form gels withdifferent inorganic metallic salts or small organic molecules in water simultaneously. Then theformed gels were characterized by the technical means of IR, SEM and XRD. The functions andmechanism of metal ions and small organic molecules played in the forming process of gel wereinvestigated.Research finds:<1>Both L1and L2can be induced by Fe³⁺to form hydrogel which arethermally reversible. Especially, the gel formed by L2was accompanied with color change in thesol-gel transition process. The photograph of SEM reveal that the structure of gel formed by L1islamellar structure and the structure of gel formed by L2is fiber mesh structure. The small-angleX-ray diffraction pattern of the dried gel show that the structures of the gel are polycrystallinestate. FT-IR spectra of the dried gel show that hydrogen bonding interactions of the gel formed byL1in the gel state may be existence; hydrogen bonding interactions of the gel formed by L2in thegel state may also be existence. When the molar ratio of L3with benzoic acid is1:12, a stablethermally reversible hydrogel can be formed. The photograph of SEM reveal that the structure ofgel formed by L3is fiber ribbon structure. The small-angle X-ray diffraction pattern of the driedgel show that the structures of the gel is polycrystalline state. FT-IR spectra of the dried gel showthat hydrogen bonding interactions of the gel formed by L3in the gel state may be existence. Withdifferent inorganic metallic salts or small organic molecules, L4can not form a gel.<2>With amide derivatives of1,3,5-benzenetricarboxylic acid for building block, a kind ofsupramolecular organic porous materials （HOF-8） was synthesized by controlling the reactionconditions. It was studied by NMR spectroscopy, Thermogravimetric analysis （TGA） and Powder X-ray diffraction （PXRD）. The results reveal that the microporous HOF-8has permanent porositywith a certain degree of framework flexibility and shrinkage of the framework. The frameworkstructure of desolvation （HOF-8d） can remain stable within240oC and has the capacity for highlyselective adsorption of C6H6and CO2at ambient temperature.