Geometric and electrochemical properties of complexes consisting of two aminonaphthoquinone-bound Schiff-base ligands and MnII, FeII, NiII, CuII, or ZnII

Novel compounds of metals (M = Mn-II, Fe-II, Cu-II, Zn-II) with aminonaphthoquinone-bound Schiff-base ligands (PyNq) were prepared with the form M(PyNq)(2). The resulting isostructural complexes formed NNN-type octahedral coordination geometry in crystals. The degree of distortion from the ideal octahedral structure depended on the ionic radius of the metal ion, with larger ions leading to greater distortion. Electrochemical studies showed that Fe-II(PyNq)(2) exhibited the greatest inter-ligand interaction of the tested compounds, resulting in a possible mixed-valence state in [Fe-II(PyNq)(2)](-). OFT calculations suggested that the efficient participation of Fell 3d orbitals in the LUMO would facilitate the inter-ligand interaction. The central metal ion was shown to be important to both the molecular and the electronic structures of the M(PyNq)(2) complexes, controlling their electron-responsive properties (redox functionalities). (C) 2014 Elsevier Ltd. All rights reserved.