Syntheses And Properties Of 2,6-/3,5-Dichlorobenzoate-based Metal-organic Complexes Tuned By Substituent Position And Transition Metal Ion

M(NO₃)₂·n H₂O/NiCl₂·6H₂O reacted with main ligand2,6-dichlorobenzoic acid(2,6-HDCB)and 4,4'-bipyridine(4,4'-bpy)auxiliary ligand under solvothermal conditions to yield six transition metal-organic coordination polymers(CPs)[Co(2,6-DCB)₂(4,4'-bpy)₂](1),[Ni₂(2,6-DCB)₄(4,4'-bpy)₄·H₂O](2),[Ni Cl(2,6-DCB)(4,4'-bpy)_1.5](2a),[M(2,6-DCB)₂(4,4'-bpy)][M=Cu(3),Zn(4)]and[Cd₃(2,6-DCB)₆(4,4'-bpy)₃·2H₂O](5).In the above reaction system,the main ligand was replaced with 3,5-dichlorobenzoic acid(3,5-HDCB)to synthesize five new transition metal-organic CPs[Co(3,5-DCB)₂(4,4'-bpy)](6),[Ni₅(3,5-DCB)₈(?₃-OH)₂(4,4'-bpy)₃](7),[M(3,5-DCB)₂(4,4'-bpy)_0.5][M=Cu(8),Zn(9)]and[Cd₄(3,5-DCB)₈(4,4'-bpy)₂](10).These eleven CPs were characterized by single-crystal X-ray diffraction,FT-IR,powder X-ray diffraction(PXRD)and thermogravimetric analysis(TGA),respectively.In these eleven complexes,2,6-DCB and 3,5-DCB connect the M(II)ions through different coordination modes to form mononuclear or multinuclear structural units,respectively,and these mononuclear or multinuclear structural units are linked by 4,4'-bpy to generate one-dimensional(1D)to three-dimensional(3D)CPs.Complexes 1 and 2have similar two-dimensional(2D)structures.Complex 2a shows a 1D double-chain structure.Complexes 3 and 4 have the same molecular formula.However,complex 3 shows a linear 1D structure,while complex 4 shows a Z-type 1D structure.Complex 5 has a trinuclear structural unit,and the adjacent trinuclear structural units are connected by 4,4'-bpy to form a 1D chain.Complex 6 has a 2D structure,and its 1D chain is formed by connecting the central metal ion with the carboxyl oxygen.Complex 7 has a unique 3D framework structure.Complexes 8 and 9 are isomorphic,showing a 1D structure.Complex 10 possesses a tetranuclear structural unit,and the adjacent tetranuclear structural units are connected by 4,4'-bpy to form a 1D chain.Thermogravimetric analysis shows that CPs 1–10 and 2a possess good thermal stability.The photoluminescent properties of CPs 1–10 and 2a and the magnetic properties of 6–8 were studied.CPs 1–10 and 2a show the characteristic fluorescent emission of organic ligands.CP 6 shows intramolecular ferromagnetic interactions between spin carriers.CPs 7 and 8display intramolecular antiferromagnetic interactions.CP 7 exhibits slow magnetic relaxation behavior under zero direct current magnetic field.