An investigation of a relatively rigid acyclic salamo-type ligand and its square planar Cu(II) complex

A relatively rigid acyclic salamo-type ligand H₂L and its square planar Cu(II) complex, [Cu(L)]·CH₃OH, were synthesized and characterized by X-ray crystallography, as well as Fourier-transform infrared spectra, UV–Vis spectra, Hirshfeld surface analyses and DFT calculations. The ligand crystallizes in monoclinic space group P 2₁/c and has pairs of intramolecular hydrogen bonds between the oxime nitrogen atoms and the hydroxyl groups. The Cu(II) complex crystallizes in the monoclinic space group P 2₁/c. The Cu(II) ion is located in the N₂O₂ cavity of the fully deprotonated salamo-type ligand (L)²⁻ unit, thus forming a four-coordinate distorted square planar geometry. At the same time, a belt-like, 2-D supramolecular structure is formed by the interaction of intermolecular hydrogen bonds, and the intermolecular interaction force is quantitatively analyzed by Hirshfeld surfaces. Significantly, fluorescence properties of the ligand and its Cu(II) complex were also studied. The coordination ratio of the Cu(II) complex was proved by UV–Vis and fluorescence titration experiments.