End-to-end thiocyanato-bridged helical chain polymer and dichlorido-bridged copper(II) complexes with a hydrazone ligand: Synthesis, characterisation by electron paramagnetic resonance and variable-temperature magnetic studies, and inhibitory effects on human colorectal carcinoma cells

The reactions of the tridentate hydrazone ligand, N'-[1-(pyridin- 2-yl)ethylidene]acetohydrazide (HL), obtained by condensation of 2-acetylpyridine with acetic hyadrazide, with copper nitrate trihydrate in the presence of thiocyanate, or with CuCl₂ produce two distinct coordination compounds, namely a one-dimensional helical coordination chain of [CuL(NCS)]_n (1) units, and a doubly chlorido-bridged dinuclear complex [Cu₂L₂Cl₂] (2) (where L=CH ₃C(O)=N-N=CCH₃C₅H₄N). Single-crystal X-ray structural determination studies reveal that in complex 1, a deprotonated hydrazone ligand L^- coordinates a copper(II) ion that is bridged to two neighbouring metal centres by SCN^- anions, generating a one-dimensional helical coordination chain. In complex 2, two symmetry-related, adjacent copper(II) coordination entities are doubly chlorido-bridged, producing a dicopper entity with a Cu···Cu distance of 3.402 (1) Å. The two coordination compounds have been fully characterised by elemental analysis, spectroscopic techniques including IR, UV- vis and electron paramagnetic resonance, and variable-temperature magnetic studies. The biological effects of 1 and 2 on the viability of human colorectal carcinoma cells (COLO-205 and HT-29) were evaluated using an MTT assay, and the results indicate that these complexes induce a decrease in cell-population growth of human colorectal carcinoma cells with apoptosis.