Synthesis, crystal structure and spectroscopic characterization of new anionic iridium(III) complexes and their interaction with biological targets

The synthesis and characterisation of new anionic iridium(II) complexes (NH4)2[IrCl4(κ2N,N'-H2biim)]2 · 5H2O (1) and ((CH3)2NH2)[IrCl4(κ2N,N’-PyBIm)] · H2O (2) are presented in this article. Spectroscopic methods (1H, 13C and 15N NMR, FTIR, UV–Vis) were used to characterize these new complexes. Solid-state structural analysis (SC-XRD) of complexes 1 and 2 shows a slightly distorted octahedral geometry of Ir(III) ions, which is constructed by one chelating κ2N,N’-2,2′-biimidazole (H2biim (1)) or 2-(2′-pyridyl)benzimidazole (PyBIm (2)) and four chloride ions. In the crystal structures, the presence of organic ligands containing NH groups favours the formation of strong hydrogen bonds (XH···Cl (X = O, N, C)), which have significant impact on the crystal structure forming 2D (1) and 3D (2) systems during the self-assembly process. Additionally, preliminary studies of the biological activity of the obtained complexes were performed. Considering the above properties, the observed stronger binding affinity of complex 1 to DNA and HSA can be interpreted in terms of changes in the number of hydrogen bonds that are potentially formed with the target molecule. Furthermore, higher reactivity towards NADH and the lower reactivity towards GSH were observed for complex 2. Both complexes showed moderate cytotoxicity against selected cancer cell lines (LoVo, MV-4–11, MCF-7) and did not show toxicity towards normal cells (BALB/3T3). The cytotoxicity of 2 may be compromised by a weaker interaction with DNA, HSA or GSH and a stronger reactivity towards NADH.