Crystal structure, spectroscopic studies, and nonlinear optical (NLO) properties of Schiff base metal complexes containing an N, S donor ligand

Article abstract of DOI:10.1139/v04-142

A new ligand, 4-dipropylaminobenzaldehyde thiosemicarbazone (abbreviated as HL), and its complexes ML₂ (M = Ni, Pd, and Cu) have been synthesized and fully characterized by elemental analyses, EI-MS, IR and UV-vis spectroscopy, and photoluminescence measurements. All of the compounds exhibit a blue-green color with dual fluorescence in DMF solution. The quantum yield ratio (Φ(CT)/Φ(LE)) decreases in the order NiL₂ > HL > PdL₂ > CuL₂. The ligand HL crystallizes in the monoclinic system, space group P2₁/n, with a = 15.1680, b = 8.5573, and c = 25.3920_A, β = 100.3457°, and V = 3242.2 A³. The nickel complex (NiL₂) crystallizes in the triclinic system, space group P1, with a = 8.3093, b = 9.7540, and c = 10.2802 A, α = 101.383°, β = 107.693°, γ = 96.703°, and V = 764.12 A³. In these complexes, HL has lost a proton from its tautometric thiol form and acts as a single negatively charged bidentate ligand coordinating to the nickel ion via the mercapto sulfur and β-nitrogen atoms. The geometry around Ni(II) is almost square-planar with two equivalent Ni-N and two equivalent Ni-S bonds. The monomeric structure of HL or NiL₂ is extended into an infinite two-dimensional network via hydrogen bonds. The two-photon absorption of HL and ML₂ solutions (in DMF) was measured at 532 nm by the open-aperture Z-scan technique.