Structural and spectroscopic studies on some metal complexes of an 8-hydroxyquinoline derivative

Mononuclear metal complexes of 2-[(2-hydroxyethylimino)methyl]quinolin-8-ol (H2L) were obtained by reaction of 8-hydroxyquinoline-2-carboxaldehyde, 2-aminoethanol and the corresponding metal(II) acetate (M = Co, Ni, Cu, Zn or Cd) in 2:2:1 molar ratios. The Schiff base ligand is acting as a monodeprotonated O,N,N-donor in the helical complex Ni(HL)2, which could be crystallographically characterised. This crystal structure contains homochiral chains of Ni(HL)2 connected through double O–H⋯O connections, which relate both non-coordinated hydroxy groups of the ethanolic arms with both phenolic O atoms of a neighbouring complex, in a “head-to-tail” disposition. A study of the luminescence properties in methanol solution showed that the quantum yields of Zn(HL)2·H2O (ΦF = 0.02) and Cd(HL)2·H2O (ΦF = 0.04) are lower than that of 8-hydroxyquinoline-2-carboxaldehyde (ΦF = 0.06).