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 (L⁰) as one of the substrates. The isolated complexes, namely, [bromido/nitrato(1.81/0.19)][tris(3,5-dimethylpyrazol-1-ylmethyl-κN²)amine-κN][cadmium/cobalt(0.96/0.04)], [Cd0.96Co0.04Br1.81(NO₃)0.19(C₁₈H₂₇N₇)] or [Cd0.96Co0.04LSBr1.81(NO₃)0.19], 1, bis{(nitrato-κO)[tris(3,5-dimethylpyrazol-1-ylmethyl-κN²)amine-κN]cobalt(II)} tetrabromidocadmate(II), [Co(NO₃)(C₁₈H₂₇N₇)]₂[CdBr₄] or [CoLSNO₃]₂[CdBr₄], 2, and (nitrato-κO)[tris(3,5-dimethylpyrazol-1-ylmethyl-κN²)amine-κN]cobalt(II) nitrate, [Co(NO₃)(C₁₈H₂₇N₇)]NO₃ or [CoLSNO₃]NO₃, 3, all contain the N-scorpionate ligand N,N,N-tris(3,5-dimethylpyrazol-1-ylmethyl)amine (LS) obtained in situ from L⁰. Compound 1 crystallizes in the monoclinic space group P2₁/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. C2/c and I2/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.