Nano structure zinc (II) Schiff base complexes of a N₃-tridentate ligand as new biological active agents: Spectral, thermal behaviors and crystal structure of zinc azide complex

In this work, synthesis of some new five coordinated zinc halide/pseudo-halide complexes of a N₃-tridentate ligand is presented. All complexes were subjected to spectroscopic and physical methods such as FT-IR, UV-visible, ¹H and ¹³C NMR spectra, thermal analyses and conductivity measurements for identification. Based on spectral data, the general formula of ZnLX₂ (X = Cl^-, Br^-, I^-, SCN^- and N₃ ^-) was proposed for the zinc complexes. Zinc complexes have been also prepared in nano-structure sizes under ultrasonic irradiation. X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were applied for confirmation of nano-structure character for the complexes. Among the complexes, zinc azide complex structure was analyzed by X-ray crystallography. This complex crystallizes as a triplet in trigonal system with space group of P3₁. The coordination sphere around the zinc center is well shown as a distorted trigonal bipyramidal with three nitrogen atoms from Schiff base ligand and two terminal azide nitrogen atoms attached to zinc ion. Various intermolecular interactions such as NH⋯N, CH⋯N and CH⋯π hydrogen bonding interactions stabilize crystalline lattice so that they causes a three dimensional supramolecular structure for the complex. In vitro screening of the compounds for their antimicrobial activities showed that ZnLI₂, ZnL(N₃)₂, ZnLCl₂ and ZnL(NCS)₂ were found as the most effective compound against bacteria of Bacillus subtilis, Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia coli respectively. Also ZnLI₂ and ZnLCl₂ complexes were found more effective against two selected fungi than others. Finally, thermal behaviors of the zinc complexes showed that they are decomposed via 2-4 thermal steps from room temperature up to 1000 °C.