Solid-Liquid Phase Structural Studies of Bis(2-Picolyl)Amine-Based Zinc(II) Complexes as Functional Hydrolase Models: The Detoxification of Fenitrothion

The reaction of the tridentate ligand bis(2-picolyl)amine (BPA) with the chloride or perchlorate salts of zinc(II) ions yielded two zinc(II) complexes of the types: [(BPA)ZnCl2]center dot 2H(2)O (1) and [(BPA)(2)Zn](ClO4)(2) (2). The intermediate complex species, namely [(BPA)Zn(OH)(H2O)](ClO4) (3) and [(BPA)Zn-OP(= S)(CH3)(2)] (4) were successfully isolated separately in good yields and pure forms. Complexes 1-4 were characterized in the solid state by using elemental analyses, thermal analyses, FT-IR, and X-ray single crystal diffraction as well as in solution by using H-1 NMR titration and cyclic voltammetry (CV). From X-ray structural and spectral features it can be concluded that the coordination environment around Zn(II) ion in 1 is a distorted square pyramidal geometry with tau(5) value of 0.148. Whereas in 2, two picolyl chelates in the equatorial plane and two slightly longer axial pyridines are coordinated in a distorted octahedral trans-facial arrangement. Kinetic studies were performed on these complexes to evaluate their efficiency as functional hydrolase models for the hydrolysis of the toxic organophosphate insecticide, Fenitrothion. The pH-dependence of the catalytic rate gives a bell-shaped curve, which gives a strong proof that the hydroxoaqua complex [(BPA)Zn(H2O)(OH)](-) 3 is the catalytically active species in the hydrolysis reactions than that of the octahedral [(BPA)(2)Zn](2+) with fully saturated coordination sphere.

Automated summary

This study investigated the chemical structures and catalytic activities of two zinc(II) complexes obtained from the reaction of bis(2-picolyl)amine with chloride or perchlorate salts of zinc(II) ions. The results showed that a specific hydroxoaqua complex exhibited higher catalytic activity in the hydrolysis reactions.