Synthesis, crystal structures, fluorescence properties, theoretical calculations and substitution effect of mono zinc(II) Schiff base complexes

Six Schiff base zinc(II) complexes were synthesized using 4-methoxyaniline/3-methyl-4-methoxyaniline, aldehydes with different substituents, and zinc chloride by a one-pot method. Their structures were characterized by FT-IR spectra, ¹H NMR spectra, elemental analysis (EA), and further by single-crystal X-ray diffraction analysis. The crystal structures of complexes Zn1–Zn5 reveal that the zinc(II) center coordinates with two nitrogen and two chlorine atoms, forming a distorted tetrahedron configuration with geometric indices of 0.87–0.90. However, the central metal adopts a five-coordinate trigonal bipyramidal configuration (τ₅ = 0.04) in complex Zn6. Solid-state fluorescence spectroscopy measurements demonstrated that complexes Zn1–Zn6 exhibit the maximum fluorescence emission in the wavelength range of 468–567 nm. Additionally, the substituent groups of the structure can modulate the emission wavelength, which was verified through density functional theory calculations.