Syntheses, characterization and third-order nonlinear optical properties of a class of thiazolylazo-based metal complexes

The reactions of a thiazolylazo ligand, 2-(2-thiazolylazo)-5-diethylaminophenol (HL) with zinc(II) chloride, nickel(II) acetate and cobalt(II) acetate resulted in the formation of the corresponding mononuclear coordination complexes, 1–3, both in solution and in the solid state. UV–Vis titration experiments in solution confirmed that the ligand and given metal salts interacted spontaneously with each other, producing exclusively mononuclear complexes with a metal/ligand ratio of 1:2. The solid-state structures of complexes 1 and 2 were determined by single-crystal X-ray diffraction analysis. In the structure of 1, zinc(II) ion is tetra-coordinate to two N atoms from the thiazolyl groups of two distinct HL ligands and two chloride counterions with a distorted tetrahedral geometry. In the structure of 2, the nickel ion is bound to four N atoms from both the thiazolyl groups and azo group moieties, and two O atoms from the phenol groups with a hexacoordinated mode. The third-order nonlinear optical (NLO) properties of both HL and 1–3 were studied by Z-scan technique in CHCl3 solution. The results showed that all four compounds exhibited strong nonlinear refraction, while complex 2 featured both large nonlinear absorption and refraction. The nonlinear refractive index values n2 of four compounds vary in the range of −1.20 × 10−18 to −3.42 × 10−18 m2/W. Their hyperpolarizability γ values are determined to be 2.01 × 10−35, 1.13 × 10−34, 2.09 × 10−34, and 7.83 × 10−34 esu for HL and 1–3, respectively, indicating that metal chelating did lead to considerable enhancement in third-order optical nonlinearities.