Four‐, five‐ and six‐coordinated transition metal complexes based on naphthalimide Schiff base ligands: Synthesis, crystal structure and properties

Abstract

Two bidentate Schiff base ligands (HL1 = N‐n‐butyl‐4‐[(E)‐2‐(((2‐aminoethyl)imino)methyl)phenol]‐1,8‐naphthalimide; and HL2 = N‐n‐butyl‐4‐[(E)‐2‐(((2‐aminoethyl)imino)methyl)‐6‐methoxyphenol]‐1,8‐naphthalimide) with their metal complexes [Cu(L1)2] (1), [Zn(L1)2(Py)]2⋅H2O (2) and [Ni(L2)2(DMF)2] (3) have been synthesized and characterized. Single‐crystal X‐ray structure analysis reveals that complex 1 has a four‐coordinated square geometry, while complex 2 is a five‐coordinated square pyramidal structure and complex 3 is a distorted six‐coordinated octahedral structure. Cyclic voltammograms of 1 indicate an irreversible Cu2+/Cu+ couple. In vitro antioxidant activity assay demonstrates that the ligands and the two complexes 1 and 3 display high scavenging activity against hydroxyl (HO•) and superoxide (O2−•) radicals. Moreover, the fluorescence properties of the ligands and complexes 1–3 were studied in the solid state. Metal‐mediated enhancement is observed in 2, whereas metal‐mediated fluorescence quenching occurs with 1 and 3.