Abstract: Four linear oxa-aza ligands, N, N ′-bis-(2-hydroxyethyl)-ethylenediamine(L¹), N-(2-hydroxybenzyl)-3-amino-1-propanol(HL²), N-(2-hydroxyethyl)-N ′-(2-hydroxy-benzyl)-ethylenediamine(HL³) and N-(2-hydroxyethyl) diethylenetriamine(L⁴), have been synthesized and characterized by elemental analyses, IR and ¹H NMR. At (25±0.1) ℃, I=0.10(KNO₃), complexation constants of Cu(Ⅱ) with L¹ and HL², and Zn(Ⅱ) with HL³ and L⁴ were determined by potentiometric pH-titration method. The results indicate that Cu(Ⅱ) forms four coordinated complexes with both L¹ and HL². Alkoxyl groups coordinate at the third coordination sites, with pK_a1 values of 7.28 for L¹ and 7.32 for HL² to become alkoxide anions. While at the fourth sites were another alkoxyl or a water molecule with pK_a2 values of 9.33 and 9.04 for L¹ and HL², respectively. Zn(Ⅱ) ions form five coordinated complexes with both HL³ and L⁴. The alkoxyl groups coordinate at the fourth sites with pK_a1 values of 7.76 and 7.96. Water molecules at the fifth sites have pK_a2 values of 9.47 and 9.57. From the above results, it can be seen that all these complexes yield nucleophiles Cu(Ⅱ)^-…ORor Zn(Ⅱ)^-…OR at neutral pH, and therefore fit the demand of double-catalysis for ester hydrolysis.

Key words: Unsymmetrical oxa-aza ligands, Copper(Ⅱ) complexes, Zinc(Ⅱ) complexes, Nuleophiles