Synthesis,Crystal Structure,and Theoretical Calculation Of Transition Metal Complexes Based On N,O Coordination

Metal complexes have rapidly developed into a research hotspot in coordination chemistry due to their diverse structures,novel topological types and superior properties.The rational selection of metal centers and organic ligands is the key to the design and construction of functional complexes,which is also a major challenge.The synthesis and characterization of ligands with nitrogen and oxygen sites and their complexes have long been of great interest in the field of coordination chemistry.It has been found that ligands containing nitrogen and oxygen sites,with more coordination sites,coordination modes and good rigidity and flexibility,can combine with metal centers to construct stable crystal frameworks.The research in this paper is as follows:1.2-Hydroxy-3-methoxybenzaldehyde monocondensates were synthesized using the reaction of o-vanillin and 1,2-phenylenediamine,and then condensed with2-formyl-8-hydroxyquinoline in a 1:1 stoichiometric ratio to obtain the8-hydroxyquinoline-substituted benzimidazole ligands H2L¹ containing N,O coordination sites,which were characterized.Six transition metal complexes were prepared by solvent volatilization method through the reaction of the ligand H2L¹with Ni（II）,Cu（II）and Zn（II）transition metal salts.Among them,the structures of complexes 1 and 2 are similar,both are mononuclear Cu（II）complexes,and the central metal Cu（II）atoms are all pentacoordinated,which are coordinated with the N,O sites of the ligands to form a distorted tetragonal cone geometry,except that there are crystalline water molecules in complex 2,and the hydrogen bonding interaction forces formed between the molecules play an important role in the structural stability of complex 2.Complex 3 is a mononuclear Ni（II）complex,with the central atom Ni1atom showing six coordination,forming a slightly distorted octahedral geometry.Complex 4 is a mononuclear Zn（II）complex with the central metal Zn（II）atoms all pentacoordinated and coordinated to the N,O sites of the ligand to form a distorted tetrahedral cone geometry.The solvent systems of complexes 5 and 6 are different and structurally similar,with the central atom Zn atom showing six coordination and forming a slightly distorted octahedral geometry.The difference is that complex 6 is composed of two ligand（HL¹）^1-units with one proton removed each,a central metal Zn（II）atom and a crystalline dichloro molecule.In terms of photophysical properties,the fluorescence properties of both ligands H2L¹ and complexes 1-6 were investigated,and fluorescence quenching effects were observed for all other complexes compared to the ligands.The intermolecular interactions were quantitatively analyzed by Hirshfeld surface analysis and two-dimensional fingerprinting.Meanwhile,the binding sites of metal ions to ligands were analyzed by molecular surface electrostatic potential.Finally,the chemical stability of ligand H2L1 and complex 1-6 was studied by density functional theory.2.The coumarin Schiff base ligand H2L² containing N,O coordination sites was synthesized from 3-formyl-4-hydroxycoumarin with 2-aminophenol in a 1:1stoichiometric ratio,and two tetranuclear complexes 7 and 8 were obtained by reaction with the metal salts Zn（OAc）₂·2H₂O and Co（OAc）₂·4H₂O,and interestingly,during the preparation of the complex crystals,the ligand H2L² was transformed from coumarin skeleton to quinoline skeleton under the in situ promotion of Zn（II）and Co（II）ions to produce a new ligand H2L²’.The new ligand obtained by this way has an excellent structure and abundant coordination sites,which is not a new idea for designing ligands.The crystal structures and coordination behaviors of 7 and 8 were also investigated.Finally,the various interactions between the complex units were analyzed in depth by Hirshfled surface analysis,and the fluorescence properties were also discussed.