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
