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

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.

Three new Schiff base complexes [Ni(HL)(L)] · (ClO4) · 0.16(H2O) (1), [ZnLZn(OOCCH3)4ZnL] (2) and [Cd2(L)2(OCH3CO)2(H2O)2] (3) have been synthesised using the Schiff base ligand and the corresponding metal ions. The Schiff base has been prepared by mixing pyridine-2-carboxaldehyde and 2-aminophenol and was isolated prior to the reaction with metal ions. Complex 1 is mononuclear, 2 is trinuclear and 3 is diphenoxo-bridged dimer. 3 forms infinite 1D chains through hydrogen bonding interactions. Only 2 and 3 exhibit strong fluorescence emission bands at 635 and 630 nm, respectively.Figure optionsDownload as PowerPoint slide