CuII complexes with co-planar [CuII(N–N)(HIMC−)], their anti-cancer activities, ΔG, ΔE and solid luminescence

Abstract

[Cu^II(phen)(HIMC⁻)(H₂O)]·[Cu^II(phen)(HIMC⁻)(NO₃⁻)]·NO₃⁻·H₂O (1) and [Cu^II(2,2′-bipy)(HIMC⁻)]·NO₃⁻·xH₂O (2) (phen = 1,10-phenanthroline, 2,2′-bipy = 2,2′-bipyridine, HIMC⁻ = 1H-imidazole-4-carboxylate acid anion) have been synthesized at 180 °C, of which the HIMC⁻ is produced by an in situ decarboxylation from H₃IDC (1H-imidazole-4,5-dicarboxylic acid) in a one-pot hydrothermal reaction. The anticancer activity experiments in vitro show that 1 exhibited excellent activities against A549, Bel-7402 and HCT-8 cancer cells and is even better than the clinical anticancer drug 5-Fu (5-fluorouracil), while 2 shows little response toward the cancer cells. The single crystal X-ray diffraction indicated that complex 1 possess a co-planar [Cu^II(N–N)(HIMC⁻)] coordination geometry. The IR, elemental analysis and solid-state luminescent spectra of complexes 1 and 2 indicated that the composition of these two complexes are similar, whereas the 2,2′-bipy in complex 2 replaced phen in complex 1. The calculation by the Gaussian 03 program illustrated that the decrease in the energy gaps between π*–π from the free to the coordinated ligand for 2,2′-bipy and phen (ΔE) are 5.3 eV to 4.0 eV and 4.8 eV to 4.5 eV separately, and the relative changes of the Gibbs free energies (ΔG) for complex 1 and 2 decomposing into free Cu²⁺ and ligands are about 0 kcal mol⁻¹ and 7 kcal mol⁻¹ respectively, which revealed that it is more stable when 2,2′-bipy is coordinated with Cu^II than phen, and 1 is easier to disassociate into free Cu²⁺ than 2. By relating the ΔE, ΔG, luminescent qualities and anticancer toxicities of the complexes with their composition, it can be concluded that both Cu^II and their coordinated ligands are responsible for the inhibition against cancer cells.