Synthesis and characterization of mononuclear and dimeric Ni(II), Cu(II) and Cd(II) Schiff base complexes with two new asymmetrical tripodal amines. Crystal structures of Ni(II) and Cd(II) complexes and their antibacterial studies

Abstract

Two new tripodal amines, 2-[(2-aminoethyl)-pyridin-2-ylmethyl-amino]ethanol (1) and 2-[(3-aminopropyl)-pyridin-2-ylmethyl-amino]ethanol (2) have been prepared. These have been used to synthesis some new Schiff base complexes by template condensation with various aldehydes in the presence of Ni(II) and Cd(II) metal ions in methanol. Five new mononuclear complexes [NiL1](ClO4), [ZnL1](ClO4), [CuL1](ClO4), [NiL2](ClO4), [NiL3](ClO4), and four new dimeric complexes [NiL4]2(ClO4)2·1.5H2O·0.5CH3CN, [NiL5]2(ClO4)2, [NiL6]2(ClO4)2 and [CdL6]2(ClO4)2 have been synthesized. All the complexes have been characterized using spectroscopic methods and the crystal structure of [NiL1](ClO4), [NiL4]2(ClO4)2·1.5H2O·0.5CH3CN and [CdL6]2(ClO4)2 were confirmed by single crystal X-ray diffraction studies. It is worth mentioning that as the chain length increases, dimeric complexes are obtained instead of mononuclear ones. Single crystal X-ray structure analysis showed that in the mononuclear Ni(II) complex, [NiL1](ClO4), the Ni(II) ion is in a distorted tetrahedral environment whilst in [NiL4]2(ClO4)2·1.5H2O·0.5CH3CN and [CdL6]2(ClO4)2, two distorted octahedral Ni(II) or Cd(II) ions are bridged asymmetrically by a pair of phenoxido groups. Also, the antibacterial activity of the synthesized Ni(II) complexes against Escherichia coli (Lio), Serratia marcescens (PTCC 1330), Staphylococcous aureus (ATCC 6633), and Proteus vulgaris (Lio) was screened. All Ni(II) complexes showed antibacterial effects and [NiL1](ClO4), [NiL4]2(ClO4)2·1.5H2O·0.5CH3CN and [NiL6]2(ClO4)2 are more effective against E. coli.