We report here the synthesis and characterization of a few phenolate-based ligands bearing tertamino substituent and their Zn(II) and Cu(II) metal complexes. Three mono/binuclear Zn(II) and Cu(II) complexes [Zn(L1)(H₂O)].CH₃OH.H₂O (1) (H₂ L1 = 6,6′-(((2-dimethylamino)ethylazanediyl)bis(methylene))bis(2, 4-dimethylphenol), [Zn₂(L₂)₂] (2) (H₂L2 = 2,2′-(((2-dimethylamino)ethyl)azanediyl)bis(methylene)bis(4-methylphenol) and [Cu₂(L3)₂.CH₂ Cl₂] (3) (H₂L3 = (6,6′-(((2-(diethylamino)ethyl)azanediyl)bis(methylene)) bis(methylene))bis(2,4-dimethylphenol) were synthesized by using three symmetrical tetradendate ligands containing N₂O₂ donor sites. These complexes are characterized by a variety of techniques including; elemental analysis, mass spectrometry, ¹H, ¹³C NMR spectroscopic and single crystal X-ray analysis. The new complexes have been tested for the phosphotriesterase (PTE) activity with the help of ³¹P NMR spectroscopy. The ³¹P NMR studies show that mononuclear complex [Zn(L1)(H₂O)].CH₃OH.H₂O (1) can hydrolyse the phosphotriester i.e., p-nitrophenyl diphenylphosphate (PNPDPP), more efficiently than the binuclear complexes [Zn₂(L2)₂] (2) and [Cu₂(L3)₂.CH₂Cl₂] (3). The mononuclear Zn(II) complex (1) having one coordinated water molecule exhibits significant PTE activity which may be due to the generation of a Zn(II)-bound hydroxide ion during the hydrolysis reactions in CHES buffer at pH 9.0.