Study On Synthesis,Structure,Properties,and Fluorescence Probes Of Salamo Type Polynuclear Metal(Ⅱ) Complexes

Salen type ligands are common chelating compounds in coordination chemistry and homogeneous catalysts.Salen type N₂O₂ ligands are typically prepared by Schiff base condensation of diamines and salicylaldehyde derivatives under heating conditions.However,the C=N bond is easily exchanged and hydrolyzed,so C=N is reversible in solution,making it difficult to obtain stable monomer compounds.By modifying Salen type ligands,oxygen atoms with high electronegativity are introduced to form oxime groups.Because the rate constant of oxime formation is several orders of magnitude larger than the rate constant of amine formation.Therefore,Salamo type ligands are more stable than Salen type ligands.Metal（II/III）complexes formed with Salamo type ligands have been significantly used in magnetism,luminescence,electrochemistry,catalysts,and ion recognition.First,a symmetric Salamo type ligand H4L¹was synthesized using1,2-di（aminooxy）ethane and 3-hydroxysalicylaldehyde,and a new tetranuclear Cu（II）complex containing four,five,and six coordination modes of Cu（II）atoms was obtained.The structure of complex 1 was characterized by single crystal X-ray diffraction.Complex 1 is a monoclinic system consisting of four Cu（II）atoms and two completely deprotonated ligand（L¹）^4-units,forming an asymmetric geometric structure.Specifically,Cu1 and Cu3 atoms coordinate with four phenoxy atoms in two ligands,respectively,forming slightly twisted planar quadrilateral geometries with four coordination points.The Cu2 and Cu4 atom are also located in the N₂O₂cavity and coordinates with one methanol molecule in the axial position,forming a five-coordinated tetragonal cone geometry.The spectral properties of the ligand H4L¹and its complex 1 were further analyzed by infrared spectroscopy,ultraviolet visible absorption spectroscopy,and fluorescence spectroscopy.In addition,electrophilic and nucleophilic sites favorable for the formation of hydrogen bonds were found through molecular electrostatic potential analysis.Hirshfeld surface analysis identified interactions in the crystal structure.In complex 1,the H···H/H···H interaction dominates,indicating that there are a large number of hydrogen bonds in complex 1.IRI analysis showed that there was a weak hydrogen bond interaction,making complex 1 more stable.Second,using 1,2-di（aminooxy）ethane and 2-hydroxy-1-naphthylaldehyde,a half-salamo type compound was first obtained,and then the ligand H2L² was obtained by reacting this half-salamo type compound with 4-（N,N￠-diethylamino）salicylaldehyde.The reaction of H2L²with Co（OAc）₂×4H₂O,Zn（OAc）₂×4H₂O and Ni（OAc）₂×6H₂O yields four trinuclear complexes 2-5,and a single crystal of the ligand.Single crystal X-ray diffraction analysis showed that complexes 2 and 3 have asymmetric trinuclear structures,with two tetradentate（L²）^2-unit receptors corresponding to three M（II）（M=Co and Zn）ions.The two terminal metal M（II）ions have five-coordinated triangular biconical geometries,and the central M（II）atom has a six-coordinated octahedral geometry.Two Ni（II）complexes have centrally symmetric trinuclear structure,and all three Ni（II）ions have six-coordinated octahedral geometries.The difference is that when methanol and ethanol are used as metal（II）salt solutions,the solvent molecules involved in the distribution of metal（II）ions are different.In addition,all complexes are represented by physical chemistry and spectroscopy.ESP analyzes the distribution of electrostatic potential in molecules to further understand electrophilic,nucleophilic reaction sites,and hydrogen bond interactions.The Hirshfeld surface analysis showed that the interaction between H···H/H···H is dominant,indicating that there are a large number of hydrogen bonds in the complexes.IRI analysis showed that there is a weak hydrogen bond interaction,making the complexes more stable.Finally,exploring the use of H2L² as a chemical sensor molecule,specifically recognizing Cu²⁺and B₄O₇^2-under the conditions of DMF:H₂O（9:1,V:V）,wherein Cu²⁺was added to the chemical sensor H₂L²to quench the fluorescence.Through DFT calculations and fluorescence UV spectroscopy titration,it is determined that the coordination ratio of H₂L²to Cu²⁺is 1:1.The addition of B₄O₇^2-to the chemical sensor H2L² enhances the fluorescence.ESP indicates that the density of the electron cloud of N and O atoms in H2L²has changed.B₄O₇^2-hydrolyzes to form borate.The electron deficiency of borate is combined with the electron donor mode of N and O atoms,and the delocalizedπbond formed by the coplanar boron oxygen atoms makes boric acid and H2L² molecules aggregate in solution.This leads to the occurrence of fluorescence aggregation induced emission（AIE）effect,which enhances the fluorescence intensity.Finally,in order to explore the application of chemical sensor H₂L²in real life,the contents of Cu²⁺and B₄O₇^2-were detected in different actual water samples,and it was found that chemical sensor H2L²can quickly and sensitively identify Cu²⁺and B₄O₇^2-.Ligand H2L²:C₂₄H₂₇N₃O₄,Mr=421.48,Triclinic system,space group P-1;Complex 1:C₃₆H₄₀Cu₄N₄O₁₆,Mr=1038.88,Triclinic system,space group P-1;Complex 2:C₁₀₇H₁₁₈Cl₆Co₆N₁₂O₂₄,Mr=2522.41,Triclinic system,space group P-1;Complex 3:C₁₄₄H₁₄₂N₁₂O₂₉Zn₆,Mr=2536.61,Monoclinic system,space group P2₁/n;Complex 4:C₅₆H₇₂N₆Ni₃O₁₆,Mr=1261.32,Triclinic system,space group P-1;Complex 5:C₆₀H₈₀N₆Ni₃O₁₆,Mr=1317.43,Triclinic system,space group P-1.