Synthesis and spectroscopic properties of two different structural Schiffbase Zn(II) complexes constructed with/without auxiliary ligands

The Schiffbase binuclear Zn(II) complexes, [Zn-2(L)(2)center dot(H2O)(2)]center dot 2DMF (1) and its coordination polymer [Zn-2(L)(2)center dot( 4,4 -bpy)(2)] ln (2) (H2L = 3-[(5-chloro-2-hydroxy-benzylidene)-amino]-4-hydroxy-chromen-2-one, 4,4' -bpy = 4,4' -bipyridine), were synthesized under the same experimental condition without or with the auxiliary ligand 4,4'-bpy, respectively. The structural analysis revealed that complexes 1 and 2 have different crystal structures. The complex 1 was a centrosymmetric binuclear structure. It is noteworthy that the linker 4,4'-bpy was introduced during the synthesis of complex 2, so that two water molecules in complex 1 were replaced by two 4,4'-bpy linkers to form one-dimensional (1D) chain-like coordination polymer. The central Zn(II) ions in complex 1 were penta-coordinated distorted square pyramid geometry with tau = 0.42. However, the Zn(II) ions of complex 2 were hexa-coordinated distorted octahedral geometry. The fluorescence spectrum showed the complex 2 containing 4,4'-bpy was substantially quenching of the fluorescence as compared with the complex 1. In addition, it could be seen from the DFT calculation the energy gaps of the complexes 1 and 2 were both reduced compared to the ligand H2L. However, the LUMO and HOMO orbits of the complex 2 were occupied by the 4,4'-bpy, which is different from complex 1, resulting in 1 and 2 had different spectral properties. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

Two Schiffbase binuclear Zn(II) complexes with different crystal structures were synthesized, with the introduction of auxiliary ligand 4,4'-bpy leading to significant changes in the structure and fluorescence properties of the complexes.