Structural studies of Schiff base ligand and its copper complexes: Solvents effect in 1-D polymeric and monomeric copper (II) complexes, computational and sensing studies

Abstract

The Schiff base ligand (E)-2,4-dibromo-6-(((2-(methylthio)phenyl)imino)methyl)phenol (SL5) and their copper complexes were synthesized. The complex-1 ([Cu (SL5) (CH3COO)]n) and complex-2 ([Cu (SL5) (CH3COO) (CH3OH)]) were obtained by inducing acetic and methanol solvent by post-synthetic modification. Both ligand and metal complexes were characterized by FTIR, SEM, and EDAX analysis. In addition, the photoluminescence behaviour has also been studied. The crystal structures of both ligand and metal complexes were determined by single-crystal X-ray diffraction studies. The structure was solved by direct methods using the SHELXS program and refined by the SHELXL program. The structural changes of ligand in the formation of the metal complexes and the solvent-induced effect of acetic acid and methanol on copper complexes have been studied using crystal structure analysis. The SL5 ligand and complex-2 crystallize in the Monoclinic, P21/n space group and complex-1 crystallize in the Tetragonal, I41/a space group. Complex-1 exhibits six coordinated distorted octahedral geometry. The addition of methanol solvent to complex-1 forms complex-2 and has five coordinated square pyramidal geometry. Complex-1 forms a 1-D coordination polymer chain via Cu1–O3 and it is replaced by the O2–H2‧‧‧O4 interaction with the aid of coordinated methanol solvent in complex-2. The effect of solvents on the coordination sphere directly influences the chelating rings. Complexes-1 exhibits interesting type-II halogen‧‧‧halogen (Br‧‧‧Br) interaction, leading to the formation of tetramer synthons (X4). Halogen-halogen interactions are broken down by adding a methanol solvent, resulting in halogen-hydrogen interactions in complex-2. Crystal structure and quantum computational studies have analyzed the synergetic effect of ligand and solvents on the molecular packing of metal complexes. The Cu(OAc)2SL5 receptor selectively detects sulfide anion in aqueous acetonitrile HEPES buffer solution in the presence of other anions. Further, antibacterial activity has been carried out for MRSA bacteria, and docking studies were carried out for penicillin-binding protein to explore the effect of coordination and solvents.