Mononuclear Ni(II) complexes of Schiff base ligands formed from unsymmetrical tripodal amines of differing arm lengths: Spectral, X-ray crystal structural, antimicrobial and DNA cleavage activity

Abstract The synthesis of two unsymmetrical N-capped tripodal amines, 2-((4-aminobutyl)(pyridin-2-ylmethyl)amino)ethanol ( 3 ) and 3-((2-aminoethyl)(pyridin-2-ylmethyl)amino)propan-1-ol ( 4 ) is reported. They feature a longer, 3-hydroxypropyl or butylamino arm than that in the analogues previously employed. All four tripodal amines, 1 – 4 , are equipped with a 2-methylpyridyl-arm, and either an ethylamino-arm ( 1 and 4 ), propylamino-arm ( 2 ) or butylamino-arm ( 3 ). The amines, 3 and 4 , have been employed in one pot condensation reactions with salicylaldehyde and its derivatives in the presence of Ni(II) metal ion. A series of new mononuclear complexes, [Ni II L aldi ](ClO 4 ) or [Ni II L aldi (solvent)](ClO 4 ) with different geometry, of Schiff base ligands were generated. X-ray crystal structure determinations of [Ni II L OMe3 (H 2 O)](ClO 4 )·2H 2 O and [Ni II L OMe4 ](ClO 4 ) revealed them to be mononuclear. The Ni(II) ion in [Ni II L OMe4 ](ClO 4 ) complex is in a distorted square-planar environment whilst this ion is in distorted octahedral environment in [Ni II L OMe3 (H 2 O)](ClO 4 )·2H 2 O complex despite the longer arm length of L 3 . While, in related systems in our previous work, they had led to dimeric complexes. These results clearly showed that the variation of the arm lengths of the ligands and metal ions has a remarkable impact on the formation and structure of the complexes. The cleavage of DNA by all synthesised complexes was examined using gel electrophoresis experiments. Also, the antibacterial effects of components were determined against the three Gram-positive bacteria, and against the three Gram-negative bacteria and against the three yeast Candida albicans ATCC 10231, Candida krusei ATCC 1424 and Candida tropicalis ATCC 13803.