Synthesis, crystal structures, and two-photon absorption properties of dithiocarbazate Zn(II) and Pd(II) complexes

A new bidentate Schiff base ligand (abbreviated as L) derived from the condensation of S-methyldithiocarbazate (SMDTC) with 9-fluorenone, and its complexes ML2 (M = Ni(II), Zn(II) and Pd(II)) have been synthesized and fully characterized by elemental analyses, IR, molar conductivity and UV–vis spectroscopy. The structures of complexes ZnL2 and PdL2 have been determined by X-ray diffraction analysis. Complex ZnL2 adopts a distorted tetrahedral geometry with the azomethine nitrogen atom and the thiolate sulfur atom. The coordination geometry about the Pd(II) is surprisingly a cis-configuration square-planar formed by the Pd(II) atom coordinating to the NS bidentate ligand. Detailed crystal structure analyses show that the cis-positioning of the two ligands was stabilized by the π–π stacking interactions between the two delocalized diazafluorene moieties. The two-photon absorption of L and ML2 solutions (in DMF) was measured at 532 nm by the open-aperture Z-scan technique.