Synthesis,Characterization And Properties Of Coordination Polymers Based On Flexible Triangle Of Aromatic Carboxylic Acid Ligand

In recent years,research on the synthesis,structure and properties of coordination polymers(CPs)has attracted a lot of attention.This is not only because the coordination polymer has a rich and varied structures,but also because of its potential application in gas adsorption,storage and separation,magnetic,fluorescent,heterogeneous catalyst and sensor.The aim of this work is to construct porous CPs with novel high-dimensional structures.Through the reactions of the flexible ligand 3,5-bis(4'-carboxyphenylmethoxy)benzoic acid(H3L)with transition metal ions or lanthanides ions,and 4,4'-bipyridine in hydrothermal condition,14 CPs have been obtained.Their structures were characterized by elemental analysis,IR,thermogravimetric analysis,X-ray single crystal diffraction and powder X-ray diffraction.Their fluorescence,magnetism,gas adsorption and photocatalysis were studied.The flexible ligand H3L has following advantages:(1)the two meta-methylene benzoic acid branches of H3L have a certain degree of freedom,which can be rotated and bent to meet the coordination requirements of different metal ions via showing cis-or trans-conformation.(2)Under different experimental conditions,the carboxylic acid may be completely deprotonated or partially deprotonated,so the carboxyl group can not only act as a hydrogen bond receptor,but also a donor.Hydrogen bond plays an important role in stabilizing 3D structure.(3)H3L is poly-dentate bridging ligand,which is easy to form a secondary structural unit and multidimensional structure.Studying the influence factors to the formation and structure of CPs,such as reaction conditions,and properties of the flexible ligand and metal ions,and exploring the relationship between the structure and properties of the new compounds,can enrich the researches on CPs of tritopic aromatic carboxylic acid and provide theoretical and experimental basis for the synthesis of novel carboxylic acid functional materials.The main results of this work are as followings:1.Four unreported CPs with 3D porous structures were synthesized by hydrothermal method using 3,5-bis(4'-carboxyphenylmethoxy)benzoic acid and transition metal ions(Mn2+,Co2+,Cu2+,Zn2+),the formulas of the four CPs are as follows:[Mn(HL)]·2H20(1)[Co(HL)]·2H20(2)(H30)[Cu2(?4-O)(L)]-H20(3)[Zn2(?3-OH)(L)]·H2O(4)1 and 2 are isostructure,in which the ligand adopts trans-configuration and its carboxyl groups adopt monodentate,bis-monodentate-bridging and ?3-bridging coordination modes.The ligands and metal ions assemble into a 3D framework with rhombic holes.In 3 and 4,metal ions form the {Zn2O)and {Cu2O}n chains via ?3-OH and ?4-O,respectively.The ligand adopts cis-configuration and coordinates to the metal ions,leading to two different 3D structures with square holes.It is the flexibility of the ligand,the coordination modes of the carboxyl groups and the nature of the metal ions itself that result in the different structures of the CPs.Different metal ions are related to different luminescence behavior and magnetic exchange properties.The optical band gap of 1-4 indicates that they are potential semiconductor materials.The nitrogen adsorption test proves that 3 has a microporous structure and there is no potential pore in 1,2 and 4.And 3 has a certain photocatalytic activity.2.Two types of lanthanides metal coordination polymers(Ln-Cps)have been synthesized by the reaction of the ligand and light(La3+,Ce3+,Nd3+)and heavy lanthanides ions(Ho3+,Er3+,Tm3+,Yb3+,Lu3+)under hydrothermal conditions.[Ln(L)]·4.5H2O(Ln = La(5),Ce(6),Nd(7),Type 1);[Ln(L)(H20)2]·3.5H20(Ln = Ho(8),Er(9),Tm(10),Yb(11),Lu(12),Type 2).This is the first time to synthesize Ln-Cps with H3L ligand and lanthanides ions under hydrothermal conditions.Due to the influence of lanthanide contraction and the coordination of carboxyl groups,the two kinds of complexes show different characteristics.In the Type 1,the lanthanides ion has a 9-coordinated three-cap triangular prism geometry,and the carboxyl group takes the ?6(?2:?1,?2:?1,?2:?1)chelating-bridging coordination mode.A 1D single strand of the right helix was formed with the repeating unit(-Lnl-L3--)n along b-axis direction,and these chains are linked by carboxyl groups to construct a 3D framework.In Type 2,lanthanides ions are in the center of double-cap triangular prism,and two coordinated water molecules are bonded at double-cap sites.The coordination of water molecules obstructs the coordination of ligand in one direction and the carboxyl groups exhibit ?4(?2,?2,?1:?1)chelate-bridging mode,thus a 2D network structure was formed.The magnetic properties,fluorescence and gas adsorption properties of partial Ln-Cps were tested.Fluorescence spectroscopy of 6,7 and 11 in the visible region showed weak fluorescence emission peaks,and 7 and 11 in the near infrared region(NIR)shows the 4f-4f characteristic emission peaks of Ln3+.The steam adsorption of methanol,ethanol and propanol on 7 and 10 were tested,both of which showed desorption hysteresis.And the amount of adsorption was related to the radius of the alcohol molecules and the pore size of the two structures.3.Two CPs with different 3D structures were synthesized by hydrothermal conditions using H3L and transition metal ions(Co2+,Ni2+)and rigid ligands 4,4'-bipyridine:[Co2(OH)(L)(bipy)]·2H20(13)[Ni(HL)(bipy)]·1.5H20(14)In 13 two crystallographically independent metal ions form a[Co4O2]unit by bridging oxygen.Furthermore,[C04O2]units connect the ligands to form a 2D network.In the direction perpendicular to the 2D plane,the[Co4O2]unit is associated with 4,4'-bipyridine to form a 1D trapezoidal strand.The 2D interlayer is connected into a 3D porous structure by Co-bipyridine stranded.A nitrogen adsorption test was performed on 13,which exhibited microporous adsorption characteristics.In 14,the central ion Ni2+ ion is coordinated with the mono-protonated carboxylic acid ligand to form a 2D layered structure.On the other hand,Ni2+ ion is coordinated with 4,4'-bipyridine to form a 1D Ni-bipyridine single chain in the a-axis direction.The 3D structure of 14 is formed by the 2D structure as a layer and 1D chain as pillar.This framework shows different pore structure from the a-,b-,c-axis directions.The ligand in 14 adopts a different cis-configuration from that of others',which has not been reported.Its formation may be attributed to the influence of the second ligand.