Investigating poly-nuclear Zn(II) and Ni(II) complexes based on a formyl-appended single salamo-type ligand

• Published in: Journal of molecular structure 2023-09, Vol.1288, p.135843, Article 135843
• Main Authors: Yan, Yuan-Ji, La, Ya-Ting, Li, Xun, Zhang, Yang, Dong, Wen-Kui, Ding, Yu-Jie
• Format: Article
• Language: English
• Subjects: Crystal structure; DFT calculation; Fluorescence property; IRI analysis; Poly-nuclear salamo-M(II) complex
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/j.molstruc.2023.135843

•Poly-nuclear Zn(II) and Ni(II) salamo-type complexes were synthesized and characterized structurally.•The decoordination sites of the aldol condensation reaction leads to the occurrence of self-assembly.•Fluorescence properties and theoretical calculations of complexes 1 and 2 were explored. Based on a salamo-type ligand H2L containing a bare formyl group, a di-nuclear salamo-Zn(II) complex [Zn2(L)Cl2] (1) was synthesized. With the occurrence of Claisen-Schmidt reaction catalyzed by triethylamine, the O4 coordination environment of the H2L ligand is destroyed, producing a new ligand H2L′. Which conflicts with the characteristics of Ni(II) atoms that are generally multi-coordinate, driving the occurrence of self-assembly reaction, and obtaining a tetra-nuclear salamo-Ni(II) complex [Ni4(L′)2(µ2-Cl)2(µ3-OMe)2(EtOH)2] (2). X-single crystal diffraction analyses showed that two Zn(II) atoms in the salamo-Zn(II) complex occupy the cavities of N2O2 and O4, respectively, while Ni1 and Ni1# atoms in the salamo-Ni(II) complex occupy the N2O2 cavities from two H2L′ ligands, there are many bridges (µ2-Cl− & µ3-OMe− aions) between Ni2 and Ni2# atoms. The UV–Vis titration experiments demonstrated the binding ratio of H2L to Zn(II) atoms is 1:2, while the binding ratio of the ligand H2L′ to Ni(II) atoms is also 1:2, the results are consistent with the X-ray single crystal structures. Through DFT calculation, the single-point energy of complexes 1 and 2 and the optimized structure of the ligand H2L were found that the softness of HOMO-LUMO gap of salamo-Zn(II) complex is small and not easy to deform, and the softness of salamo-Ni(II) complex is large and easy to deform, which is in agreement with the calculated results of intra-molecular interactions in IRI. The interaction of a large number of hydrogen bonds, C-H…π, π…π, van der Waals forces and so on in salamo-Ni(II) complex makes it easy to deform. The fluorescence properties of H2L and the salamo-Zn(II) complex have also been studied. Based on a salamo-type ligand H2L containing a bare formyl group, a di-nuclear salamo-Zn(II) complex [Zn2(L)Cl2] (1) was synthesized. With the occurrence of the Claisen-Schmidt reaction catalyzed by triethylamine, the O4 environment of the H2L ligand is destroyed, producing a new ligand H2L'. Which conflicts with the characteristics of Ni(II) atoms that are generally multi-coordinate, driving the occurrence of self-assembly reaction, and obtaining a tetra-nuclear salamo-Ni (II) complex