Synthesis, structures and fluorescence of nickel, zinc and cadmium complexes with the N,N,O-tridentate Schiff base N-2-pyridylmethylidene-2-hydroxy-phenylamine

Abstract

Mono-, tri- and dinuclear neutral complexes [Ni(HL)(L)] . (ClO₄) . 0.16(H₂O) (1), [ZnLZn(OOCCH₃)₄ZnL] (2) and [Cd₂L₂(OCH₃CO)₂(H₂O)₂] (3) have been obtained from the reaction between the potentially tridentate N,N,O-donor Schiff base ligand HL, where HL = N-2-pyridylmethylidene-2-hydroxy-phenylamine with nickel, zinc or cadmium salts, respectively. The ligand has been prepared by 1:1 condensation of pyridine-2-carboxaldehyde and 2-aminophenol. The ligand and metal complexes were characterised by elemental analysis, spectroscopic studies such as IR, UV-Vis, ¹H NMR, fluorescence, electrochemical and magnetic susceptibility measurement. The structures of the three complexes have been determined by single-crystal X-ray diffraction. The nickel ions in 1 show a distorted mer-octahedral geometry. In 2, the terminal zinc ions have coordination geometry midway between square pyramidal and trigonal bipyramidal, whilst the central zinc ion has slightly distorted octahedral geometry. The trinuclear unit is held together by bridging deprotonated phenolic oxygen atoms from the Schiff base and acetate groups. In 3, two monocapped-octahedron cadmium ions are held together by μ₂-diphenoxo bridges. Among the three synthesised complexes, 1 is nonfluorescent while the other two can serve as potential photoactive materials as indicated from their characteristic fluorescence properties.