Synthesis, crystal structures, spectral studies and reactivity of square planar copper(II) complexes containing Schiff base ligand

The reactions of HL¹ [2-((2-(benzylthio)phenylimino)methyl) phenol] and HL² [3-((2-(benzylthio)phenylimino)methyl)-2-hydroxy-5- methylbenzaldehyde] separately with Cu(OAc)₂·H₂O afforded new Cu(II) complexes [Cu(L¹)(OAc)] (1) and [Cu(L ²)₂] (2), respectively. These are characterized by microanalytical data and spectroscopic studies. UV-vis spectra of the complexes show intense low-energy transitions ∼ 420 nm which are ligand to metal charge transfer (LMCT) transitions. The single-crystal X-ray structures were determined for 1 and 2. Reactions of [Cu(L¹)(OAc)] (1) with, SCN ^- and show the replacement of weakly coordinated acetate yielding [Cu(L¹)(N₃)], [Cu(L¹)(SCN)] and [Cu(L ¹)(NO₂)], respectively. Unequivocal characterization of the substituted products has been done by single-crystal X-ray study of [Cu(L¹)(N₃)]. HL² and its Cu(II) complex exhibited low-intensity emission bands at ∼575 nm upon excitation at 375 nm and at 420 nm, respectively. Redox properties of the complexes were determined electrochemically. Density functional theory (DFT) computations have been carried out to explain the spectroscopic and redox properties of the complexes.