LAUSR

Abstract A new Schiff base, HL, derived from condensation reaction of 2,4-dihydroxybenzaldehyde and 4-amino-3-methyl-1H-1,2,4-triazole-5(4H)-thione together with its Ni(II) complex have been synthesized and characterized by several spectroscopies methods. The optimized geometries, assignment of the IR bands and NMR chemical shifts as well as exploring of the frontier orbitals of two synthesized compounds have been calculated using the density functional theory (DFT) procedures. The most stable tautomer of the HL Schiff base and kinetics of its tautomerization have been explored theoretically. In the square planar structure of the [Ni(L)Cl] complex, the anionic L- acts as a NOS tridentate ligand. The chloro ligand is positioned trans to the azomethine nitrogen. The DFT-computed IR frequencies and NMR chemical shifts are good in agreement with their corresponding experimental values, approving validity of the optimized geometries for two investigated compounds. The [Ni(L)Cl] complex exhibits high catalytic activities in a three-component cyclocondensation for synthesis of the tetrahydrobenzo [b]pyrans.