Studies On Polynuclear Copper(Ⅱ),Cobalt(Ⅱ),and Nickel(Ⅱ) Complexes Constructed From Bis(Salamo)-Type Compounds And Their Fluorescence Probes

In recent years,various types of multi-dentate chelating ligands,especially those containing nitrogen,oxygen and sulfur elements,have been extensively designed for the formation of structurally novel metal（Ⅱ/Ⅲ）complexes,as well as for the development of their potential applications in various fields.Salen-type ligands are an important class of multifunctional chelating ligands obtained by Schiff base condensation reactions,and their excellent properties are highly appreciated by scholars.As more and more research has been conducted,it has been found that the defects of Salen-type ligands themselves have greatly limited their applications.Salamo-type ligands are obtained by modification of Salen-type ligands.The stability of the ligand molecule is improved by the introduction of a more electronegative oxygen atom,while the presence of its unique N₂O₂ cavity can be coordinated with a variety of metal（Ⅱ/Ⅲ）ions to form structurally rich metal complexes,making them more widely used.First,the centrosymmetric methoxydisubstituted bis（salamo）-type rigid ligand H4L¹ was synthesized and characterized by ¹H NMR.Complex 1 was successfully synthesized by the reaction of ligand H4L¹ with Cu Cl₂·2H₂O.The crystal data show that complex 1 is a binuclear Cu（Ⅱ）complex[Cu₂（L）（H₂O）₂]with space group P21/n.In addition,the complex 1 was characterized by infrared,UV-Vis,and fluorescence spectroscopy.Theoretical calculations and molecular electrostatic potential surfaces（MEPs）were analyzed for ligand H4L¹ and complex1 using density generalization theory.Finally,Hirshfeld surface and interaction region index（IRI）analyses of ligand H4L¹ and complex 1 were performed to clarify the various intermolecular interactions of complex 1,which corroborate with its crystal structure.Next,complexes 2 and 3 were obtained using the reaction of the ligand H4L¹ with Co（OAc）₂·4H₂O and Ni（acac）₂ transition metal salts.The structures of complexes 2 and 3 were characterized using X single crystal diffraction.Both complexes 2 and 3 are tetranuclear structures,and the introduced anion-assisted ligands are involved in coordination in different coordination modes.The weak interactions and linkage properties between complexes 2 and 3were analyzed using molecular electrostatic potential surfaces,Hirshfeld surfaces,and interaction regions.Then,a chemosensing study was conducted on H4L¹,which can be used as a"fluorescence-on"type chemosensor to identify HCO₃^-and CO₃^2-.The binding constant Ka,the limit of detection LOD and the limit of quantification LOQ of HCO₃^-and CO₃^2-by H4L¹ were calculated.Meanwhile,the sensing mechanism of HCO₃^-and CO₃^2-recognition by the chemical sensor H4L¹ was investigated by fluorescence titration spectroscopy,Job’s working curve analysis and high-resolution mass spectrometry.Finally,based on the study of the chemosensor H4L¹,the sensor H4L² was synthesized,which can interact with Cu²⁺and HSO₄^-and can selectively recognize Cu²⁺and HSO₄^-by fluorescence burst effect without the interference of other anions.The limit of detection（LOD）,limit of quantification（LOQ）and binding constant K_a for Cu²⁺and HSO₄^-were calculated by fluorescence titration spectroscopy and the Benesi-Hildebrand equation,and the mechanism of Cu²⁺and HSO₄^-recognition by the chemical sensor H₄L² was investigated.