Crystal structures, cytotoxicity studies and interactions with DNA of novel in situ -formed complexes containing N -scorpionate ligands and nitrate ions

This article presents a comprehensive investigation involving the synthesis and characterization of three complexes obtained in an efficient one-pot synthesis using zero-valent cobalt and the proligand 1-hydroxymethyl-3,5-dimethylpyrazole (L 0 ) as one of the substrates. The isolated complexes, namely, [bromido/nitrato(1.81/0.19)][tris(3,5-dimethylpyrazol-1-ylmethyl-κ N 2 )amine-κ N ][cadmium/cobalt(0.96/0.04)], [Cd 0.96 Co 0.04 Br 1.81 (NO 3 ) 0.19 (C 18 H 27 N 7 )] or [Cd 0.96 Co 0.04 L S Br 1.81 (NO 3 ) 0.19 ], 1 , bis{(nitrato-κ O )[tris(3,5-dimethylpyrazol-1-ylmethyl-κ N 2 )amine-κ N ]cobalt(II)} tetrabromidocadmate(II), [Co(NO 3 )(C 18 H 27 N 7 )] 2 [CdBr 4 ] or [CoL S NO 3 ] 2 [CdBr 4 ], 2 , and (nitrato-κ O )[tris(3,5-dimethylpyrazol-1-ylmethyl-κ N 2 )amine-κ N ]cobalt(II) nitrate, [Co(NO 3 )(C 18 H 27 N 7 )]NO 3 or [CoL S NO 3 ]NO 3 , 3 , all contain the N -scorpionate ligand N , N , N -tris(3,5-dimethylpyrazol-1-ylmethyl)amine (L S ) obtained in situ from L 0 . Compound 1 crystallizes in the monoclinic space group P 2 1 / n , and some positional disorder is observed at the metal ions and inorganic ligands. In contrast to 1 , compounds 2 and 3 form ionic crystals and crystallize in the same type of space group (No. 15) but in different settings, i.e. C 2/ c and I 2/ a , respectively. The synthesized compounds were characterized by X-ray diffraction, elemental analysis and FT–IR spectroscopy. All the complexes presented here have good biological activity against cancer cells. Among the complexes studied, 2 and 3 are the most interesting. The interactions of isolated complexes 2 and 3 with CT-DNA were investigated using UV–Vis absorption spectroscopy and circular dichroism (CD). Isolated complexes 2 and 3 interact with CT-DNA via nonintercalatory binding modes. The results show that complex 2 combines high anticancer potency with selective action towards colorectal adenocarcinoma cells and is more effective than complex 3 and the anticancer drug cisplatin. These properties make complex 2 an interesting candidate for further investigation of specific anticancer mechanisms.