Schiff base ligands derived from 1,2-bis(2′-nitro-/amino-phenoxy)-3-R-benzene and 2-hydroxy-1-naphthaldehyde and their Cu/Zn(ii) complexes: synthesis, characterization, X-ray structures and computational studies

Abstract

1,2-Bis(2′-nitrophenoxy)-3-R-benzenes {R = H (1), CH3(2) and OCH3(3)} have been prepared from the SNAr reaction between 1-fluoro-2-nitrobenzene and 3-R-catechol (aromatic diol), and are then reduced to the corresponding diamines 1,2-bis(2′-aminophenoxy)-3-R-benzene {R = H (4), CH3(5) and OCH3(6)}, respectively. Reaction of these diamines with 2-hydroxy-1-naphthaldehyde gives tetradentate Schiff base ligands {H2L: R = H (H2L1), CH3(H2L2) and OCH3(H2L3)}, respectively. The Schiff base ligands coordinate to metal(ii) ions to provide the complexesML1,ML2andML3(M = Cu and Zn), respectively. X-ray molecular structure determinations were performed to explore stereochemical rigidity as the origin of chirality induction in the dinitro (2), diamine (5) and Schiff base ligands (H2L1andH2L2) as well as in the complexes (ZnL2,ZnL3andCuL3), respectively. The structures feature an N2O2-chromophore from bis(2-oxo-1-naphthaldiminate) moieties with one additional weak Cu/Zn⋯O (ether) contact to give a 4 + 1 coordination with a distorted square-pyramidal geometry forZnL2,ZnL3andCuL3, respectively. Without considering this additional contact, the structures are distorted tetrahedral or distorted square-planar for the Zn or Cu complexes, such that a chiral Λ- and Δ-configuration at the metal atom is induced. All three metal complexes crystallize as a crystalline racemate or racemic mixture ofΛ/Δ-ML. The supramolecular packing in the structures is organized by inter-/intra-molecular π-π and C-H⋯π interactions, respectively. The optimized structures and excited state properties from DFT/TDDFT calculations support the experimental results. © The Royal Society of Chemistry 2021.