Preparation And Properties Of Supramolecular Metallogels Based On Pyridine Amide Ligands

As a new type of smart soft material,stimulus-responsive supramolecular metallogel has attracted more and more attention in many fields such as biomedicine,sensors and molecular motors.In this dissertation,the preparation of visible light-responsive and ion-responsive supramolecular metal gels are the goal.Based on pyridine amide ligands,a series of supramolecularmetallogels were are prepared.The selectivity of these supramolecular metallogels to anions and the photo responsive properties of the composite materials composed of metallogel and metastable photoacid mPAH2 were studied.The metastable photoacid mPAH2 was synthesized by the reference method.The dark acidity(pKa(MeOH)=8.75)and photo acidity(pKa*(MeOH)=3.39)of mPAH2 were determined by spectrophotometry with 9-aminoacridine(or 4-dimethylaminopyridine)and methyl orange as reference bases,respectively,which can help to select organic ligands with suitable basicity to construct supramolecular metallogel and to exchange protons with mPAH2.Four pyridine amide type ligands were synthesized and characterized:N,N'-bis-4-pyridinyl-isophthaloyl chloride(L1),N,N'-bis(4-pyridinyl carbonyl)-2,6-diaminopyridine(L2),N,N'-bis(4-pyridinyl carbonyl)-m-phenylenediamine(L3)and N,N',N"-tri(4-pyridyl)trimesic amide(L4).In DMSO-H2O(v/v=1/1,the same below)medium,L1 could form supramolecular metallogel with CuCl2 and CuBr2,the critical gelation concentration(CGC,wt%)is 0.782%and 2.65%,respectively.In DMF-H2O(v/v=1/1,the same below)medium,L1 could form supramolecular metallogels with CuCl2,CuBr2 and AgNO3,with CGC being 1.055%,1.94%and 0.577%,respectively.However,in both mediums,L1 and Cu(NO3)2 could not form supramolecular metallogel,and the system showed selectivity to Cl-and Br-,respectively.In DMSO-H2O medium,L1,CuBr2 and mPAH2 formed the metallogel-photo acid composite with the concentrations of 0.016,0.128 and 0.0061 M,respectively.The color of the composite changed obviously after being irradiated with 470 nm visible light for 20 min,proving that mPAH2 can undergo photochemical reaction in the medium and the gel tends to soften visually.However,the color of the composite could not be completely restored after being placed in the dark overnight,which may be related to the strong basicity of the ligand.In DMSO-H2O medium,L2 could form three supramolecular metallogels with CuCl2,AgNO3 and AgSO3CF3,respectively.The CGC of the three gels were 0.5%,0.5%and 0.7%,respectively.However,in this medium,L2 and CuBr2 could not form supramolecular metallogel,and the system showed selectivity to Cl-.The comparative experiments showed that L2 and CuBr2 could form supramolecular metallogel with the same molar of NaCl as Br-present.In DMSO-H2O medium,ligand L2 could not form supramolecular metallogel with CoCl2,Co(CH3COO)2 or Co(NO3)2.However,in DMF-H2O medium,L2 reacted with CoCl2,Co(CH3COO)2 or Co(NO3)2 to form three stable metallogels immediately with the addition of the co-ligand sodium oxalate,with CGC being 3.6%,3.9%and 5.4%,respectively.In DMSO-H2O medium,ligand L3 could form supramolecular metallogels with CuCl2 or CuSO4,with the CGC being 1.03%or 1.51%,respectively.Under the experimental conditions,to form stable metallogels,the molar ratio of CuCl2/L3 ranged from 2:1 to 28:1,while that of CuSO4/L3 ranged from 4:1 and 8:1.It could be seen that the kind of the anions played an important role to form metallogels based on Cu2+ and L3,which may stemed from the strength of the metal-anion coordination.