Fluorescent Chemosensors for Selective and Sensitive Detection of Phosmet/Chlorpyrifos with Octahedral Ni2+ Complexes

The hexadentate ligands H(2)L1-L3 with mixed S, N, O donor sites and possessing substituents having either "no" or electronreleasing/withdrawing nature at terminal ends are synthesized. The ligands H(2)L1-L3 were tested for binding with library of metal ions, wherein maximum efficiency was observed with N-i2+, and it motivated us to prepare the Ni2+ complexes. The ligand H(2)L1 underwent deprotonation and formed binuclear complex when interacted with Ni2+ as evident from its crystal structure. The H(2)L2 and H(2)L3 having electron-withdrawing/electron releasing groups, respectively, were also deprotonated; however, they afforded mononuclear complexes with Ni2+ ion. This signifies the importance of steric parameters instead of electronic factors in these particular cases. Impressed by differential behavior of complexes of H(2)L1 and H(2)L2/H(2)L3 with Ni2+ and their photophysical and electrochemical properties, all the metal complexes were studied for their chemosensing ability. Nowadays with increased use of organophosphate, there is alarming increase of-these agents in the environment, and thus we require efficient technique to estimate the level of these agents with high sensitivity and selectivity in aqueous medium. The Ni2+ complexes With hydrophobic nature were suspended into aqueous medium for testing them as sensor for organophosphate. The (L-1)(2)center dot(Ni2+)(2) could sense phonnet with detection limit of 44 nM, whereas L-2.Ni2+ and L-3.Ni2+ exhibited the detection limits of 62 and 71 nM, respectively, for chlorpyrifos.