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 (HL 1 = N ‐ n ‐butyl‐4‐[( E )‐2‐(((2‐aminoethyl)imino)methyl)phenol]‐1,8‐naphthalimide; and HL 2 = N ‐ n ‐butyl‐4‐[( E )‐2‐(((2‐aminoethyl)imino)methyl)‐6‐methoxyphenol]‐1,8‐naphthalimide) with their metal complexes [Cu(L 1 ) 2 ] ( 1 ), [Zn(L 1 ) 2 (Py)] 2 ⋅H 2 O ( 2 ) and [Ni(L 2 ) 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 Cu 2+ /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 (O 2 −• ) 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 .