Synthesis, structural characterizations and theoretical calculations of the Ni(II) complex based on a novel Salamo-Salen-Salamo-type hybrid ligand

Abstract

The Salen compound is a typical Schiff base ligand, and by combining one Salen-structure unit with two Salamo-structure units, a novel hybrid Salamo-Salen-Salamo-type ligand H4L was synthesized. The synthesis of corresponding complexes based on the hybrid ligand was studied. Ni(II) ion participates in coordination and synthesizes a hybrid Salamo-Salen-Salamo-type mononuclear complex [Ni(LH2)]. X-ray single crystal diffraction analysis showed that Ni(II) ion has coordinated with Salen N2O2 structure, forming a planar geometry with tetracoordination. The Salamo structure units are not involved in coordination, and two Salamo long chains are spatially close to each other and there are N, O atoms that are easy to coordinate with metals, forming a potential coordination environment. The spectral properties of the complex was further discussed by IR and UV-vis spectroscopy, and the binding ratio of the ligand H4L to Ni(II) ion in solution was verified by UV-vis titration spectroscopy. Through the structural optimization of the ligand and single-point energy calculation of the complex, the HOMO-LUMO gaps of the ligand and the complex were analyzed to determine the softness of the ligand and the complex. TD-DFT analysis of the ligand and its complex was found to be consistent with experimental results, and the energy level transition sources of the main absorption peaks and their contributions were analyzed. The interaction force within the molecule of the Ni(II) complex was calculated, and finally the movable free region of the complex molecule in the unit cell was calculated and displayed.