Synthesis And Properties Of Rare Earth Phosphite-Oxalates Acid Compound

Phosphorus-based metal oxides?MPOs?are an important member of microporous materials due to their diverse structure and attractive properties such as photoluminescence,catalysis,adsorption,membranes,nonlinear optics,proton conduction and ion exchange.It is getting more and more important.And the M-O-P linkages has good stability,can obtain a strong inorganic framework and exhibit good hydrothermal stability.Recently,attempts have been made to replace phosphate with a phosphite with fewer connectivity,with the expectation of a more open and interesting structure.Rare earth metal create conditions for a variety of energy level transitions due to their own 4f electronic layers.Therefore,materials containing lanthanides can exhibit unique properties in the fields of magnetism and photoluminescence,and have the reputation of materials treasure house.Therefore,the lanthanide metal phosphite-oxalate series has certain research value.In this paper,different organic amines and amino acids were selected as structure-directing agents.Under the condition of hydrothermal or solvent-free,the synthesis and design of new lanthanide metal phosphite-oxalic acid compounds were explored,and the properties of fluorescence and proton conduction were further studied.Provide theory and reference for the development of new proton conductive materials.In this paper,different organic amines and amino acids were selected as structure-directing agents.Under the condition of hydrothermal or solvent-free,the synthesis and design of new lanthanide metal phosphite-oxalic acid compounds were explored,and the properties of fluorescence and proton conduction were further studied.Provide theory and reference for the development of new proton conductive materials.Firstly,two different structures of LnPO₄ materials were synthesized by using N,N'-dimethylpiperazine as a structure-directing agent.Among them,thelanthanidephosphorousacid-oxalate{[Ln₂?C₂O₄?₃?H₂PO₃?₂](C₆H₁₆N₂)·2H₂O Ln=Gd³⁺?1?,Tb³⁺?2?and Dy³⁺?3?}?Compound 1-3?were synthesized under hydrothermal conditions;The hydrazine phosphite Ho?H₂PO₃?₄(C₆N₂H₁₆)_0.5?compound 4?was synthesized under the condition of solvent-free synthesis.Compounds 1-3 have a three-dimensional open framework structure with two types of 12-ring channels in the ab and bc planes,respectively,in which water molecules are present.Therefore,compounds 1-3 should exhibit good proton conduction.Under high temperature and high humidity conditions,the proton conductivity was 1.10×10^-3 S cm^-1,1.94×10^-3 Scm^-1,1.07×10^-3 Scm^-1,respectively.The effect of different humidity on the activation energy was also investigated.At the same time,compound 2 showed four characteristic emission bands at 488,544,585 and 620 nm at 354 nm excitation wavelength,and the four bands are assigned to the transition of ⁵D₄?⁷F_J?J=6,5,4,3?.Compound 3 was excited at 296 nm and showed typical yellow luminescence of Dy³⁺ions.Compound 4 synthesized a novel one-dimensional chain structure modified by phosphorous acid unit using the solvent-free synthesis method conforming to the green chemical concept.The compound in which each helium atom is bonded to four[HPO₃^2-]units to form a pleated4-membered ring-like structure,and the[H₂PO₃^2-]pseudotetrahedron modifies the one-dimensional chain.It is worth noting that there are left and right hand spiral chains in the structure.Secondly,a novel Ln-MOF material La₂?C₂O₄??C₆H₉N₃O₂??H₂O?·?H₂O?_n?compound 5?was successfully synthesized under hydrothermal conditions with L-histidine as ligand.The compound has a three-dimensional open framework structure.L-histidine is modified as a ligand on both sides of the wavy shikimate chain to form a three-dimensional open framework by oxalic acid bridge.Additionally,compound 5 shows photoluminescence property in solid state.Finally,two novel cobalt phosphite-oxalates with different framework,which are isomeric and of stoichiometry Co?H₂PO₃??C₂O₄?·?C₂H₈N??6 and 7?,Compound 6 is a 2D layered structure.The 2D layer contains a 12-MR windows.7 is a 3-dimensional open framework with different 12-MR windows channels in the ac plane and the bc plane,respectively.The2-dimensional layer formed in the ac plane is very similar to the2-dimensional layer of Compound 6.The difference is that in compound 6,a pair of[H₂PO₃]^-pseudo-tetrahedrons are connected to two adjacent cobalt atoms in the zigzag cobalt oxalate chain,while compound 7 is a[H₂PO₃]^-pseudo-tetrahedrons and a serrated cobalt oxalate chain by two adjacent cobalt atoms are connected.The effect of mixed solvents on crystal synthesis is also discussed.The variable temperature magnetic susceptibility test showed that the compounds 6 and 7 have a certain antiferromagnetic property.