Novel 1D chain Fe(III)-salen-like complexes involving anionic heterocyclic N-donor ligands. Synthesis, X-ray structure, magnetic, ⁵⁷Fe Mössbauer, and biological activity studies

The iron(III) salen-type complexes [Fe(salen)(L)]_n (1–6) involving heterocyclic N-donor ligands HL {HL = 1H-imidazole (Himz), 1H-tetrazol-5-amine (Hatz), 5-methyl-1H-tetrazole (Hmtz), 1H-benzimidazole (Hbimz), 1H-1,2,4-triazole (Htriz) and 1H-benzotriazole (Hbtriz)} have been prepared and characterised by elemental analysis, FT IR, CI mass and ⁵⁷Fe Mössbauer spectroscopies, and variable temperature magnetic measurements. Single crystal X-ray analysis of [Fe(salen)(btriz)]_n (6) revealed a 1D chain-polymeric structure of the complex with the btriz anion as a bridging ligand. Magnetic data for all complexes were fitted using Fisher's model (for S = 5/2) and also using a heptanuclear closed ring model showing a weak antiferromagnetic interaction (J≈−1 to −2 cm⁻¹), and moreover, molecule-based magnet properties have been observed in the case of [Fe(salen)(atz)]_n (2). The exponential correlation between the magnetic properties (the isotropic exchange parameter J) and the basicity of the free ligands (K_b) has been found. The antiferromagnetic ordering as well as a moderate structural dissimilarity in the vicinity of iron atoms has been proved by the ⁵⁷Fe Mössbauer low-temperature (2 K) in-field (7 T) experiments in the case of (2), in which two sextets with the line intensities (3/4/1/3/4/1) have been observed. The compounds have been tested for their SOD-like activity, DNA cleavage activity, and in vitro cytotoxicity against two human cancer cell lines: chronic myelogenous erythroleukemia (K562) and breast adenocarcinoma (MCF7). The best result regarding the cytotoxicity has been achieved for the complex of [Fe(salen)(atz)]_n (2), where IC₅₀ = 6.4 μM against K562.