Three supramolecular trinuclear nickel(II) complexes based on Salamo-type chelating ligand: syntheses, crystal structures, solvent effect, Hirshfeld surface analysis and DFT calculation

Abstract

Three Ni(II) complexes {[NiL(μ-OAc)(CH₃CH₂OH)]₂Ni} (1), {[NiL(μ-OAc)(CH₃OH)]₂Ni]·2CH₂Cl₂·2CH₃OH (2) and {[NiL(μ-OAc)(CH₃OH)]₂Ni}·1.5CH₃OH (3) based on a Salamo-type bis-oxime ligand (H₂L = 2,2′-[ethylenedioxybis(nitrilo-methylidyne)]dinaphthol) have been synthesized and characterized by physicochemical and spectroscopic methods. The complexes 1, 2 and 3 are all trinuclear structures, and the center Ni(II) ions are six-coordinated and show the slightly distorted octahedral coordination. They all consist of three Ni(II) ions, two deprotonated L^2- units, two μ-acetato ligands and two coordinated solvent molecules, as well as the crystallizing solvent molecules. Although the molecular structures of the Ni(II) complexes 1, 2 and 3 are similar to each other, obtained in different solvents, the supramolecular structures are entirely different. The complexes 1, 2 and 3 possess the self-assembled infinite 1D, 3D and 2D supramolecular structures via different intermolecular interactions (hydrogen bonds, C–H···π and π···π stacking interaction), respectively. But complex 2 formed a 3D structures by intramolecular hydrogen bonds. It is significant that the solvent molecules have obvious effects on the optical properties and molecular configuration. The Hirshfeld surface analysis showed that the short-range forces of the hydrogen bonds in complexes 1, 2 and 3 accounted for 67.8%, 44.6% and 52.7%, respectively. The molecular orbital energies for ligand H₂L and complex 1 were obtained by DFT calculation, and the electron distribution, energy level and energy gap of HOMO and LUMO were given.