A new thiosemicarbazone and its 3d metal complexes: Synthetic, structural, and antioxidant studies

2-[1-Oxo-1-(piperidin-1-yl)propan-2-ylidene]- N-(prop-2-en-1-yl)hydrazinecarbothioamide (HL) and its six coordination compounds [Cu(L)X] (X = Cl− (1), NO3− (2)), [Cu(A)(L)NO3](A = 1,10-Phen (3), 2,2′-Bpy (4)), [Ni(HL)2](NO3)2 (5), and [Fe(L)2]Cl (6) are synthesized and characterized by elemental analysis, Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), and single-crystal X-ray crystallography. Uncoordinated thiosemicarbazone HL shows higher antioxidant activity against 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS+•) cation radicals compared with most of the other complexes. Complex 5 is the most active and its activity exceeds that of HL and is close to that of trolox, which is used in medicine as an antioxidant. The introduction of N-heteroaromatic bases (1,10-phenanthroline and 2,2′-bipyridine) into the inner sphere of the complex [Cu(L)NO3] did not lead to an increase in antioxidant activity.