Unusual coordination mode of 3-methoxysalicylaldehyde in mononuclear zinc(II) complexes with nitrogenous bases: Synthesis, structural characterization and theoretical studies

The reaction of the new precursor compound [Zn(3-OCH3-salo)2(H2O)2] (1) with the nitrogenous bases enR afforded the Zn(II) compounds [Zn(3-OCH3-salo)2(enR)] (2–5), where 3-OCH3-salo is the anion of 3-methoxysalicylaldehyde (o-vanillin) and enR the neutral bipy, phen, neoc and dpamH ligands. The new compounds were characterized by physicochemical and spectral (FT-IR, UV–Vis, 1H NMR) data. The X-ray diffraction study of [Zn(3-OCH3-salo)2(bipy)]·CH3OH (2) and [Zn(3-OCH3-salo)2(dpamH)] (5) confirmed the coordination mode of the 3-OCH3-salo ligand to the zinc cation through the phenolate and methoxy oxygen atoms, as predicted from the spectroscopic data. The thermal stability of the compounds [Zn(3-OCH3-salo)2(enR)] was investigated by the simultaneous TG/DTG-DTA technique and compared with the precursor (1). The residue at 1000 °C was estimated from TG curves as a carbonaceous mixture of ZnO. The molecular structure, the alternate coordination mode of 3-OCH3-salo ligand, the isomerism and the energetics of the metal–ligand interactions for compounds 2 and 5 have been studied by means of density functional theory (DFT) calculations.

The compounds [Zn(3-OCH3-salo)2(H2O)2] (1) and [Zn(3-OCH3-salo)2(enR)] (2–5), were synthesized and characterized. The unusual coordination mode of the ligand, through the phenolate and methoxy oxygen atoms, was confirmed by X-ray studies. The alternate coordination mode of 3-OCH3-salo, the isomerism and the energetics of the metal–ligand interactions were studied by DFT calculations.Figure optionsDownload as PowerPoint slide