Studies On The Synthesis, Characterization And Application Of The 2,6-Diaminopyridine Schiff Base Complexes

Schiff base and its complexes are widely used in the fields of biology, catalysis and material etc. Thus, studies on the synthesis of novel Schiff base complexes and their characterization and application are significant to the development of coordination chemistry.Three novel Schiff base ligands which were derived from 2,6-diaminopyridine -salicylaldehyde (H₂L¹), 2,6-diaminopyridine- vanillin (H₂L²), 2,6-diaminopyridine-benzaldehyde have been prepared(L³), and fifteen coordination compounds of transition metal with these ligands have been synthesized. These ligands and complexes were characterized by elemental analysis, IR spectra, UV spectra, TG-DTG and molar conductance analysis, and the suggested structures of the complexes were concluded. Fluorescence of Schiff base ligands and their complexes of Cd²⁺, Zn²⁺ , Ni²⁺ have been studied. Bioactivities of the novel complexes including the scavenging activity to O₂^-·and intercalation action with DNA have been studied.The compositions of the metal complexes with Schiff base ligand 2,6-diaminopy ridine- salicylaldehyde (H₂L¹) are confirmed to be: [Cu(HL¹)(CH₃COO)]·H₂O; [CoCHL¹)(CH₃COO)]·H₂O; [Mn(HL¹)(CH₃COO)]·H₂O; [Cd(HL¹)(CH₃COO)]·H₂O; [Ni(HL¹)(CH₃COO)]·H₂O; [Zn(HL¹)(CH₃COO)]·H₂O.The compositions of the metal complexes with Schiff base ligand 2,6-diaminopy ridine- vanillin (H₂L²) are confirmed to be: [Cu(HL²)(CH₃COO)]·H₂O; [Co(HL²)(CH₃COO)]·H₂O; [Mn(HL²)(CH₃COO)]·H₂O; [Zn(HL²)(CH₃COO)]·H₂O; [Cd(HL²)(CH₃COO)]·H₂O.The compositions of the metal complexes with Schiff base ligand 2,6-diaminopy ridine- benzaldehyde have been prepared(L³) are confirmed to be: [NiL³L⁴(CH₃COO)]·H₂O;[CdL³L⁴(CH₃COO)]·H₂O; [CoL³L⁴(CH₃COO)]·H₂O; [ZnL³L⁴(CH₃COO)]·H₂O.The synthesis of ligand and complexes was in non-aqueous solvents. All the ligand and complexes were are all stable and could be preserved in the air for a long time. The complexes are colored and powered substance and difficult to dissolve in the water. The nitrogen atom, oxygen atom of hydroxybenzene and carboxyl of Schiff base were all coordinated to the metal ions. Water molecules are exists as crystal water. The carboxyl is coordinated to the metal ions in a mondentate or bidentate fashion.Combinating Achar differential and Coats-Redfern integral method which fits the thirty kinetic equations, the calculating program was designed. The kinetic equations of thermal decomposition for complexes and the corresponding kinetic parameters were gained. The kinetic parameters include E,A, order of reaction and correlation coefficient, etc. The activation entropyâ–³S^≠and activation free-energyâ–³G^≠for some thermal decomposition stage were also calculated.The thermal decomposition kinetic function of [Co(HL¹)(CH₃COO)]·H₂O in step(2) may be expressed as f(α)=1/3(1-α)[-ln(1-α)]^-2, and the kinetic equation of thermal decomposition may be expressed as:dα/dt=Aexp(-E/RT)f(α)=Aexp(-E/RT)1/3(1-α)[-ln(1-α)]^-2 , E=449.49 kJ/mol,lnA=74.19, r=0.9986,â–³S^≠=468.66 J/mol·K,â–³G^≠=139:24 kJ/mol;The thermal decomposition kinetic function of [Cu(HL²)(CH₃COO)]·H₂O in step(3) may be expressed as f(α)=3/2(1-α)^2/3[1-(1-α)^1/3]^-1, and the kinetic equation of thermal decomposition may be expressed as:dα/dt=Aexp(-E/RT)f(α)=Aexp(-E/RT)3/2(1-α)^2/3[1-(1-α)^1/3]^-1, E=760.29kJ/mol, lnA=148.37, r=0.9929,â–³S^≠=983.05 J/mol·K,â–³G^≠=185.99kJ/mol;The thermal decomposition kinetic function of [CdL³L⁴(CH₃COO)]·H₂O in step(3) may be expressed as (α)=2(1-α)[1-ln(1-α)]^1/2, and the kinetic equation of thermal decomposition may be expressed as:dα/dt=Aexp(-E/RT)f(α)=Aexp(-E/RT)2(1-α)[1-ln(1-α)]^1/2, E=366.78 kJ/mol, lnA=44.43, r=0.9946,â–³S^≠=141.84 J/mol·K,â–³G^≠=260.85 kJ/mol.The excitation and emission peak wavelengths(λ_ex/λ_em) of the Schiff base coordination compounds of [Ni(HL¹)(CH₃COO)]·H₂O,[Zn(HL²)(CH₃COO)]·H₂O and [CdL³L⁴(CH₃COO)]·H₂O are 528nm/530nm; 367nm/368nm; 488nm/490nm respectively in fluorescence spectra. Compared with the ligands, the excitation peaks and the emission peak of [Ni(HL¹)(CH₃COO)]·H₂O and [Zn(HL²)(CH₃COO)]·H₂O have changed, and the fluorescence intensity increases, and the excitation peaks and the emission peak of [CdL³L⁴(CH₃COO)]·H₂O are similar with the ligand.electron absorption spectrum analysis and fluorescene spectrum analysis were used to determine the bioactivities of some complexes, respectively. The results show that some complexes bear the scavenging activity to O₂^-·and intercalation action with DNA.