Synthesis and properties of schiff base metal complexes from amine and salicylaldehyde derivatives

Abstract

Hexadentate Schiff base zinc (II) and nickel (II) complexes were synthesized from the reaction between salicylaldehyde or salicylaldehyde derivatives, metal (II) acetate and triethylenetetramine at the mol ratio of 2:1:1. Protonation constants of Sal[subscript 2]trien, Sal[subscript 2](OMe)trien, Sal[subscript 2](OEt)trien and stability constants of their zinc and nickel complexes were determined by potentiometric titration technique using 1.00 x 10[superscript -2] M Bu[subscript 4]NCF[subscript 3]SO[subscript 3] in methanol at 25 ํC. Stability constants in term log beta are 4.56 +- 0.05, 4.30 +- 0.11, 3.76 +- 0.09 for ZnSal[subscript 2]trien, ZnSal[subscript 2](OMe)trien, ZnSal[subscript 2](OEt)trien and 4.80 +- 0.17, 5.77 +- 0.14, 7.08 +- 0.03 for NiSal[subscript 2]trien, NiSal[subscript 2](OMe)trien, NiSal[subscript 2](OEt)trien, respectively. The stability constants of nickel complexes are higher than those zinc complexes which indicates that nickel complexes are more stable than zinc complexes. This result corresponds to the Irving-William sequence, which describes that the order of stability constant for metal complexes from different cation is Cu[superscript 2+] > Ni[superscript 2+] > Zn[superscript 2+]. The structures of Sal[subscript 2]trien, Sal[subscript 2](OMe)trien, Sal[subscript 2](OEt)trien, ZnSal[subscript 2]trien, ZnSal[subscript 2](OMe)trien and ZnSal[subscript 2](OEt)trien were optimized by Density Functional Theory (DFT) calculation using 6-31G(d) basis set. Total of thermodynamic energies of Sal[subscript 2]trien, Sal[subscript 2](OMe)trien, Sal[subscript 2](OEt)trien and their zinc complexes were computed at B3LYP/6-31G(d) level of theory