Exploration of DFT and Hirshfeld analyses and fluorescence properties of three stable penta-coordinated binuclear Co(II) and Zn(II) bis(salamo)-based complexes

Abstract

A new symmetrical multi-halogen-substituted bis(salamo)-based tetraoxime ligand H3L and its corresponding penta-coordinated homo-binuclear Co(II) and Zn(II) complexes have been successfully synthesized. The three complexes, [{Co2(L)(OCH3)}2]·CHCl3 (1), [{Zn2(L)(OCH3)}2]·CH3OH (2) and [{Co2(L)(OCH2CH3)}3]·2CH3CH2OH·CHCl3 (3), have been characterized by elemental analyses, FT-IR and UV–Vis absorption spectroscopy as well as X-ray single-crystal structure analyses. In complexes 1 and 2, two crystallographically independent but chemically identical binuclear complex molecules A and B were detected by X-ray analysis. However, in complex 3, three crystallographically independent but chemically identical binuclear complex molecules A, B and C were detected. All the penta-coordinated Co(II) and Zn(II) atoms in complexes 1 and 2 are located in the N2O2 cavities of the completely deprotonated (L)3- units and coordinated to one oxygen atom from one μ2-bridged methoxyl group. The coordination environment of the Co(II) atoms in complexes 1 and 3 are similar, except that the μ2-bridged methoxyl group is replaced with the μ2-bridged ethoxyl group. Additionally, both of complexes 1 and 3 form 3D supramolecular structures through abundant intermolecular interactions, while complex 2 forms 1D supramolecular structure through intermolecular hydrogen bonds. The CH···π interactions have been established in complexes 1 and 2, where the π-system of H3L participates as π-donor. Through the means of Hirshfeld surfaces and 2D fingerprint plot analyses, existing different non-covalent supramolecular interactions in the Co(II) and Zn(II) complexes have been explained. Furthermore, to obtain a better understanding of the fluorescence properties of H3L and its complexes 1–3, fluorescence titration experiments have been performed.