An efficient one-pot synthesis of pyrazole complexes formed in situ: synthesis, crystal structure, Hirshfeld surface analysis and in vitro biological properties.

The molecular crystals of monomeric and dimeric pyrazole complexes were prepared via one-pot syntheses. These are dichloridobis(3,5-dimethyl-1H-pyrazole-κN¹)cobalt/zinc(0.2/0.8), [Co_0.20Zn_0.80Cl₂(C₅H₈N₂)₂] or [Co_0.2Zn_0.8Cl₂(3,5-dmp)₂] (1), and bis(μ-3,5-dimethyl-1H-pyrazole)-κ²N¹:N²;κ²N²:N¹-bis[bromido/chlorido(0.7/0.3)bis(3,5-dimethyl-1H-pyrazole-κN¹)cobalt/zinc(0.1/0.9)], [Co_0.20Zn_1.80Br_1.40Cl_0.60(C₅H₇N₂)₂(C₅H₈N₂)₂] or [Co_0.1Zn_0.9Br_0.7Cl_0.3(μ-3,5-dmp)(3,5-dmp)]₂ (2). The isolated complexes contain 3,5-dimethylpyrazole (3,5-dmp) ligands formed in situ from the decomposition of 1-hydroxymethyl-3,5-dimethylpyrazole. In both isolated complexes, some positional disorder is observed at the metal ions and halogen ligands. The molecular crystals of 1 and 2 are centrosymmetric, with the space groups C2/c and P-1, respectively. Additionally, in the dinuclear complex, the pyrazole ring has a bridging coordination function with respect to the metal ions. Both complexes have good biological activities against cancer cells. The results of an in vitro cytotoxicity study indicated that compounds 1 and 2 showed significant cytotoxicity for cancer cell lines, including hepatic (HepG2 cells), lung (A549 cells) and colon cancer cells (SW 480 and SW 620). Based on the calculated IC₅₀ values against human cancer cell lines, it was found that both complexes demonstrated potent antiproliferative activity combined with great selectivity towards cancer cells. Complex 2 was a more effective cytotoxic agent which, at the same time, exhibited high cytocompatibility. The obtained data are very encouraging and could be useful for anticancer drug discovery.