Studies On The Structures And Properties Of Complexes Of 3,5-Dicarboxyphenylboronic Acid And Its In-Situ Generated Ligand

Metal-organic frameworks（MOFs）,having regular pores,large specific surface area and strong adsorption capacity,have become a research hotspot for their potential applications in selective separation,catalysis,ion exchange,sensors,and fluorescence.In this research,seven targeted MOFs were prepared from the solvothermal reations of 3,5-dicarboxyphenylboronic acid with transition metal and rare earth metal ions,the structures and properties of which were explored.3,5-Dicarboxyphenylboronic acid contains carboxyl group having strong coordination ability and also electron-deficient group of-B（OH）₂.It was used in this research to prepare MOFs with promising application aspects.H₂L¹,H₂L² and H₂L³ represent 3,5-dicarboxy-phenylboronic acid,5-chloroisophthalic acid and isophthalic acid,respectively.1.Five two-dimensional frameworks were synthesized from the reactions of3,5-dicarboxyphenyl boronic acid ligands with the rare earth metal ions of Dy³⁺,Er³⁺,Gd³⁺,Tb³⁺,respectively.The complexes 1-4 have smilar structures.Their metal ions are surrounded by coordinating atoms to form distorted double-capped trigonal prism geometries.The two carboxyl groups on the ligand（L¹）^2-behave as syn-syn and syn-anti bridging modes,respectively,to connect two metal ions.The two adjacent metal ions are bridged by two carboxyl groups from two 3,5-dicarboxyphenylboronic acid ligands to build dinuclear units which are further linked by oxalate ions to form one-dimensional chains.The interactions of these one-dimensional chains through the coordination of oxlate ions lead to the construction of the two-dimensional network structure of complexes 1-4.The complex 5 is also a 2-D Dy complex prepared using3,5-dicarboxyphenylboronic acid as ligand,in which the metal ion form distorted mono-capped trigonal prism geometries.The two carboxyl groups on the ligand（L¹）^2-have syn-syn and syn-anti bridging modes.The two adjacent Dy³⁺ions are bridged by four carboxyl groups from four ligands to form a[Dy₂（COO）₄]²⁺dinuclear building block,which is further linked to another four ones through（L¹）^2-to form a two-dimensional network structure.The solid fluorescence results showed that the（L¹）^2-ligand can be used as excellent sensitive reagents for effectively sensitizing Tb³⁺luminescence,which suggests its potential application as photoluminescent materials.The photocatalytic results showed that complex 2 has an inhibitory effect on the photocatalytic degradation of methylene blue dyes.The magnetic measurement results showed that complexes 1,2 and 4 have no slow relaxation behavior as revealed by the absence of frequency-dependent ac susceptibilities.2、The use of 3,5-dicarboxyphenylboronic acid as the precursor to react with copper chloride gave a Cu₂₄ nanocage cluster 6 bearing the linker of5-chloroisophthalic acid which was in-situ generated from 3,5-dicarboxyphenyl-boronic acid due to the cleavage of the unstable C-B bonds in the reaction.The two carboxyl groups on（L²）^2-act as syn-syn bridge to link two adjacent Cu（II）ions.Two adjacent metal ions are bridged by four carboxyl groups to form a dinuclear unit[Cu₂（COO）₄],which is further linked to another four ones through（L²）^2-ligands to form a twenty-four nuclear cage structure.In the solution state fluorescence study,complex 6 has a high recognition effect on Fe³⁺,while the fluorescence intensity of complex 6 decreases with the increase of Fe³⁺ion concentration.A further analysis of the relationship between the fluorescence intensity and the Fe³⁺ion concentration in the quenched state revealed that the nanocage has a large quenching constant.The photocatalytic results show that complex 6 has an inhibitory effect on the photocatalysis of methylene blue dyes.3、The use of 3,5-dicarboxyphenylboronic acid as a precursor to react with copper nitrate gave a dinuclear-based two-dimensional Cu（II）framework complex 7of isophthalate.The ligand in this complex was in-situ generated from3,5-dicarboxyphenylboronic acid due to the cleavage of the unstable C-B bonds in the reaction.The two carboxyl groups on（L³）^2-act as syn-syn bridge to link two adjacent Cu（II）ions.Two adjacent metal ions are bridged by four carboxyl groups to form a dinuclear unit[Cu₂（COO）₄],which is further linked to another four ones through four（L³）^2-ligands to form a two-dimensional structure.Its photocatalytic studies on the degradation of methylene blue dyes showed that complex 7 has weak catalytic effect on the degradation of methylene blue dyes.