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

Abstract

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=CH3C(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.

Transition Metal Complexes with 1‐Adamantoyl Hydrazones – Cytotoxic Copper(II) Complexes of Tri‐ and Tetradentate Pyridine Chelators Containing an Adamantane Ring System

“…[24][25][26][27][28][29][30][31] The significant difference in the degree of polyhedron distortion can be expressed through the τ 5 parameters, [32] which are in the range 0.02(1)-0.24 (2) The different dimerization methods are manifested in the internuclear distances between the copper atoms. Thus, in 2 and 4, in which the chlorido anions play a bridging role, the Cu internuclear distances are 3.4085(8) and 3.2926(5) Å, respectively, and are comparable to those in structurally related complexes, [22,23] whereas in 4, in which Addpy-H act as the bridging ligand, the Cu internuclear distance is significantly larger [5.4841 (5) The coordination polyhedron of the monomeric neutral complex 2 is a distorted square pyramid. Addpy is coordinated as an ONN-tridentate ligand in its neutral form.…”

“…Thus, 2 and 4 have nearly rectangular Cu 2 (μ-Cl) 2 cores, similar to that found in other copper(II) complexes with the ONNtridentate hydrazones 2-acetylpyridine benzoylhydrazone [22] and 2-acetylpyridine acetylhydrazone. [23] In 5, the fourth basal position is occupied by a N-coordinated thiocyanato ion, whereas the apical site is occupied by the N4 pyridinic nitrogen atom of a tetradentate μ-Addpy ligand. Analogous behavior has been reported for di(2-pyridyl) ketone Schiff bases.…”

Crystal structures and magnetic properties of a set of dihalo-bridged oxalamidato copper(ii) dimers

“…It has been shown that exchange interaction is affected by several structural parameters such as the identity of the bridging atoms (X), the Cu-Cu' distances, the bridging angles Cu-X-Cu' (α), the dihedral angles containing Cu ions and the coordination geometries around copper ions. 5,9,[45][46][47][48][49] For planar dihydroxo-bridged copper complexes, a simple, linear, correlation between the singlet-triplet separation 2J and the angle α was reported. [45][46][47] However, in the case of dihalo-bridged copper complexes, the wider variety of geometries available to such systems and the possibility for relatively low-lying halogens' d-orbitals to interact with copper orbitals make the overall picture more complicated.…”

Electron Paramagnetic Resonance as a Tool for Studying the Mechanisms of Paramagnetic Anticancer Metallodrugs

“…A cytotoxic Cu II quinolone complex, for example, exhibited only dimeric species in the solid state but showed signals corresponding to a population of monomeric Cu II species in aqueous solution . Similarly, whereas the X‐ray crystal structures of cytotoxic Cu II complexes with tridentate pyrazole‐based ligands, and thiocyanato‐bridged Cu II and Co II (low‐spin, d 7 , S = 1 / 2 ) hydrazone complexes,, , indicated dimeric species, monomers were detected in solution by EPR.…”