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 n(2) of four compounds vary in the range of -1.20 x 10(-18) to -3.42 x 10(-18) m(2)/W. Their hyperpolarizability gamma values are determined to be 2.01 x 10(-35), 1.13 x 10(-34), 2.09 x 10(-34), and 7.83 x 10(-34) esu for HL and 1-3, respectively, indicating that metal chelating did lead to considerable enhancement in third-order optical nonlinearities. (C) 2011 Elsevier B. V. All rights reserved.