Syntheses,Structures And Properties Of Functional Coordination Polymers Based On Triazole-carboxylic Acid Ligands

In this paper,two kinds of triazol-carboxylic acid ligands,3,5-bis?triazol-1-yl?benzoic acid?HL1?and 2,4-bis?triazol-1-yl?benzoic acid?HL2?,were selected as organic ligands.Six coordination polymers based on the two ligands and transition metal ions were synthesized under solvothermal conditions.The structures and related properties of the complexes were characterized by single-crystal X-ray diffraction,FTIR,thermogravimetric and solid/liquid fluorescence.Complex 2,4 and 5 can selectively detect Fe³⁺ and Cr⁶⁺ in aqueous solution as fluorescence sensors,and compound 4 can also effectively identify DMSO molecule.Additionally,complex 2 can efficiently adsorb Congo red?CR?in the aqueous solution,and 5 shows good adsorption capacity to Methylene Blue?MEB?.Now the main content is listed as below.1.Three kinds of new complexes based on 3,5-bis?triazol-1-yl?benzoic acid?HL1?,[Co?L1?2?2H₂O?]?3H₂O?1?,[Zn?L1?2?2H₂O?]?4H₂O?2?and Cd?L1?2?H₂O?3?,were prepared by solvothermal reaction.And complex 4 was synthesized with 2,4-bis?triazol-1-yl?benzoic acid?HL2?and Zn?NO3?2.The two ligands self-assemble with different metal salts to form four different structures eventually.In complex 1,2and 4,the carboxyl oxygen atoms of HL1 and HL2 are uncoordinated,and each metal ion coordinates with four nitrogen atoms from four different ligands and two water molecular ligands.Because the coordination planes of adjacent metal ions and nitrogen atoms in complex 1 and 2 are close to perpendicular angle,the‘concave-and-convex' type of one-dimensional chain is formed.But in complex 4,the related coordination plane is coplanar,which results in a linear one-dimensional chain.At last,due to different hydrogen-bonded patterns,complex 1 forms a two-dimensional supramolecular structure while complex 2 generates a three-dimensional structure,and complex 4 is a zero-dimensional structure.And complex 3 finally exhibit a stable three-dimensional framework with a?2,3,4?-connection of {4.82}{4.86.102.12}{8} topology.Comparing these structures,itcan be found that the structure dimension is higher and the thermal stability is better when the carboxyl group is involved in the coordination.Studying of solid fluorescence emission spectra shows that complex 2 and 4 have excellent luminescence performance.Therefore,the fluorescence response of complexes to different cations and anions were tested and the results show that Fe³⁺ and Cr⁶⁺ almost completely quenched the fluorescence of 2 and 4.It is obvious that complex 2 and 4can be used as qualified fluorescent probes to selectively recognize Fe³⁺?LOD: 0.10 m M?and Cr⁶⁺?LOD: 0.10 m M?in aqueous solutions.In addition,the dye adsorption experiments display that 2 has an eminent selectively adsorption effect on the anionic dye of Congo red,and the adsorption efficiency is 97.84%.2.Two kinds of new complexes based on 3,5-bis?triazol-1-yl?benzoic acid?HL1?and 1,3,5-benzenetricarboxylic acid?H3bta?,[Zn2L1bta?3H₂O?]?H₂O?5?and[Cd2L1bta?3H₂O?]?4H₂O?6?,were prepared by solvothermal reaction.Complex 5 and6 are isomorphic frameworks,in which metal ions are chelated with two kinds of ligands to form a mononuclear?Cd1?and a binuclear structure?Cd₂O₄?separately.Each Cd1 can be considered as a three-connection and each Cd₂O₄ as a six-connection,and the ligand HL1 and H3 bta can be used as three-connections.Complex 5/6 finally shows a?3,6?-connection of {63}6{66;86;102;12} topology.TGA shows that the structure of complex 5 and 6 started to collapse at 250 ?,which is very ocompound1 and 4.Complex 5 has good luminescence performance,so the fluorescence emission spectra of 5 in different cations and anions were testified.Experimental results show that 5 can selectively detect Fe³⁺?LOD: 0.11 m M?and Cr⁶⁺?LOD: 0.10 m M?in aqueous solutions by fluorescence quenching.The fluorescence quenching constant of Fe³⁺ reaches up to 104.Dye adsorption experiments show that 5 and 6 can adsorb Congo red in aqueous solutions,and 5 can also efficiently adsorb Methylene Blue and Acridine Orange with the adsorption efficiency being 97.64% and 97.64%respectively.In addition,complex 5 also possesses good adsorption capacity to Rhodamine B,Crystal Violet and Malachite Green,which may be attributed to the‘breathing' effect of the framework.