New Zn(II) and Cu(II) complexes with in situ generated N2O2 siloxane Schiff base ligands

Two novel mononuclear zinc(II) and copper(II) complexes of tetradentate N2O2 Schiff base ligands generated in situ by the template method were synthesized by the reaction of salicylicaldehyde and o-vanillin, respectively, with 1,3-bis(3-aminopropyl)tetramethyldisiloxane and the corresponding metal salts, in the presence of pyridine. The structures of the metal complexes were determined by elemental and spectral (IR, UV–Vis, ESI-MS) analyses as well as by single crystal X-ray diffraction, revealing a tetrahedral coordination geometry around the copper and zinc atoms ensured by the N2O2 donors of the Schiff bases. The crystalline structures are stabilized by intermolecular π–π stacking and short C–H⋯π interactions, which generate supramolecular polymeric chains. The absorption and emission properties of the complexes were studied in solution. The antimicrobial activity was assayed in vitro against three fungi and two bacteria species. Both complexes are moisture stable, as was proved by vapor sorption (DVS) analysis. The catalytic activity of the complexes was evaluated in the decomposition reaction of hydrogen peroxide.

Graphical abstractTwo bis(hydroxy-azomethine) ligands with the highly flexible 1,3-bis(propyl)tetramethyldisiloxane spacer and differing by the carbonylic precursor (salicylicaldehyde or o-vanillin) were prepared and used to complex zinc(II) and copper(II) ions. The formed mononuclear complexes were structurally characterized. Their photophysical, biological and catalytic activities, as well as moisture behavior, were evaluated.Figure optionsDownload full-size imageDownload as PowerPoint slide