Synthesis And Properties Of Lanthanide Metal Organic Framework Materials Based On Aromatic Tetracarboxylic Acids

The lanthanide metal-organic frameworks?Ln-MOFs?have become one of hotpots in the field of coordination chemistry and materials science because they can combine the fascinating properties of lanthanide?III?ions and the unique structure of metal-organic frameworks.It is of great significance to construct lanthanide metal-organic frameworks with novel structures and various functions and explore their applications in the fields of luminescence,magnetism,electrical conductivity,gas adsorption separation,chemical sensor and catalysis.In this paper,twelve Ln-MOFs are synthesized by two kinds of rigid aromatic polycarboxylic acids.Their structures are characterized and analyzed in detail,and their functions are explored in combination with structural features.The main results are as follows:By using aromatic tetracarboxylic acids of biphenyl-3,3',5,5'-tetracarboxylatic acid?H₄bptc?and 1,3,6,8-tetrakis?4-carboxylphenyl?pyrene?H₄TBAPy?and diverse rare earth salts,a series of three-dimensional Ln-MOFs?1-8 and 9-12?were synthesized through the solvothermal methods.Structurally,1 and 2 crystallize in the chiral trigonal space group P3₁2₁and P3₂2₁.Neutral framework 3 crystallizes in the monoclinic space group C2/c.CO₂ and HCOO^-originating from the decomposition of DMF participate in the coordination of 4-8?4and 5 crystallize in the triclinic space group P,6-8 crystallize in the monoclinic space group C2/m?.The asymmetric unit of anion framework 9-12 consists of five Ln^IIIII ions which display different coordination geometries with coordination numbers of 7,8 and 9.Different combinations of chelating,bridging bidentate??₂-?¹:?¹?and chelating bidentate??₂-?²:?¹?of two ligands result in structural diversity.The properties of Ln-MOFs with H₄bptc ligand were studied.1 is Ln-MOF with magnetic refrigeration and proton conduction:-?S_m is 26.36 J kg^-11 K^-11 at 2 K and 7 T and the proton conductivity is 2.92×10^-44 S cm^-11 at 60 ^oC and 98%RH.2 is a multifunctional Ln-MOF with magnetic,fluorescent and dye-exchange properties.In magnetic measurement,there is a field-induced slow magnetic relaxation with energy barriers(U_eff)of 48.19 K.It both displays strong fluorescent emissions under excitation at 328 nm,which are typical emission bands of Dy^?ions.And as an anionic framework,it has specific selective adsorption for cationic dye rhodamine B due to the appropriate pore size.The Ln-MOFs with H₄TBAPy ligand emit strong yellow-green light under excitation light because of a rigid planar center.After forming complexes,enhanced rigidity of frameworks and weaker conjugate effect cause a certain blue shift in fluorescence.Fluorescence measurements show that there is a concentration-dependent fluorescence blue shift phenomenon.10 can selectively sense nitrobenzene and acetylacetone based on turn-offand turn-on effect,respectively.It is a potential multifunctional chemo-sensor which also can selectively detect aspartic acid?Asp?based on turn-on effect.