Design,Synthesis,Structure Characterization And Properties Of Metal Organophosphonic Acid Complexes

Metal organic framework materials(MOFs)have broad application prospects in adsorption,catalysis,fluorescence,magnetism and proton conduction.Therefore,it is of great significance to design and synthesize new organic acids ligands and complexes,explore the relationship between structure and properties,and screen out new materials with practical application value.In this paper,two kinds of organic phosphonic acid ligands C₆H₅-(CH₂)₂-N(CH₂PO₃H₂)₂(H₄L¹)and NH₂-(CH₂)₂-COH(PO₃H₂)₂(H₅L²)were synthesized as main ligands,coordinated with 4,4'-bipy,seven new organic phosphonic acid complexes,which have not been reported,were synthesized by hydrothermal method,and the magnetic and photocatalytic properties were studied.The coordination polymers synthesized based on the two organic phosphonic acid ligandsare:Co₂(L¹)·2H₂O]·0.178H₂O(1),[Cu₂(L¹)·2H₂O]·0.457H₂O(2),Mn₃(HL¹)·4H₂O(3),Co[(4,4'-bipy)(H₄L¹)·4H₂O]·2H₂O(4),Co[(4,4'-bipy)(H₄L¹)·4H₂O]·2H₂O(5),Co(H₄L²)₂(6)and Cu₃(H₂L²)₂?4H₂O(7).The structure of the complex was characterized by elemental analysis,IR,XRD and single crystal X-ray single crystal diffraction.Thermal stability analysis(TGA)showed that the complexes 1,2,6,and 7 all have high thermal stability.According to their structural characteristics,two of the complexes 1 and 2 were selected for their magnetic and photocatalytic properties.The magnetic properties of the complexes 1 and 2 were analyzed.The magnetic susceptibility(?_m)of complexes 1 and 2 decreased with the increase of temperature in the range of the applied magnetic field of 1 k Oe and the temperature range of 2-300 K.And two kinds of magnetic behavior curves are drawn,that is,the relationship between?_mT and T and?_m^-1 and T.The data show that the values of?_mT and?m^-1 increase with the increase of temperature.In order to better reveal the magnetic behavior,the magnetic fitting was carried out by using PHI program and the linear fitting was carried out by using Curie-Weiss law[?_mT=C/(T-?)](C is Curie constant,and?is extras constant).In summary,both complexes 1 and 2 magnetically exhibit antiferromagnetic properties.The properties of complexes 1 and 2 for degrading methylene blue dyes were investigated.By Solid Ultraviolet Diffuse Reflectance Absorption Spectrum and Valence Band X-ray Photoelectron Spectrum,the energy band gap between the highest occupied orbit(HOMO)and the lowest unoccupied orbit(LUMO)of the two complexes was calculated to be 3.72 e V and 2.51 e V,respectively,the valence band values EV were calculated to be 1.78 e V and 2.01 e V,respectively,and the value EC were calculated to be-1.94 e V and-0.5 e V,respectively.Under the synergistic action of ultraviolet irradiation and trace hydrogen peroxide,the two complexes had good degradation effect on methylene blue.The degradation rate of complex 2 was faster than that of complex 1,and the degradation rate reached 98.21%in 40 minutes.The influencing factors of the reaction were discussed through comparative experiments.The main influencing factors were p H of the reaction solution and the amount of hydrogen peroxide added.The results showed that p H=6.85 and hydrogen peroxide 30 UL had the best degradation effect.The degradation rate of complex 1 was 97.78%in 60 minutes and that of complex 2 was98.21%in 40 minutes.The first-order kinetics model(ln(C/C₀)=-K₁t)was fitted for the degradation of methylene blue by complexes 1 and 2 under ultraviolet irradiation.The results showed that the degradation ability of complexes 1 and 2 accorded with the first-order kinetics model,and the first-order reaction rate constants of complexes 1 and 2were 0.00165 min^-1 and 0.00188 min^-1,respectively.The valence band spectra of the complexes 1 and 2 to degrade MB were analyzed to estimate the active substances(h⁺,·OH and·O₂^-).The free radical trapping experiment was carried out,and the OH cleaning agent t-Bu OH,·O₂^-capture agent NBT and hole scavenger TEOA were added and calculate the degradation rate.The results showed that the main active substances of complexes 1 and 2 degraded MB were holes and·O₂^-.