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

Authors:

• Despoina Anastasiadou,
• Ariadni Zianna,
• Maria Gdaniec,
• Michael P. Sigalas,
• Evdoxia Coutouli-Argyropoulou,
• Agnieszka Czapik,
• Maria Lalia-Kantouri

Abstract

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.