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

Abstract The reaction of the new precursor compound [Zn(3-OCH 3 -salo) 2 (H 2 O) 2 ] ( 1 ) with the nitrogenous bases enR afforded the Zn(II) compounds [Zn(3-OCH 3 -salo) 2 (enR)] ( 2 – 5 ), where 3-OCH 3 -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, 1 H NMR) data. The X-ray diffraction study of [Zn(3-OCH 3 -salo) 2 (bipy)]·CH 3 OH ( 2 ) and [Zn(3-OCH 3 -salo) 2 (dpamH)] ( 5 ) confirmed the coordination mode of the 3-OCH 3 -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-OCH 3 -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-OCH 3 -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.