Synthesis, characterization and bioactivity of a novel iron(III) 18-metallacrown-6 complex with S-donor ligands

The reaction of 4-salicyloyl thiosemicarbazide (H3st) (1) with FeCl3 · 6H2O in methanol solution gives a novel 18-metallacrown-6 [Fe(st)(H2O)]6 · 21H2O (2). The structure containing S–Fe bonds was determined for 2 by using X-ray crystallography. The ring of the metallacrown was consisted of six interlink [Fe–N–N] repeated units. And the ligand enforces the metal ions to form the stereochemistry as a propeller configuration with alternation Λ/Δ form. The largest diameters of the disc-shaped hexanuclear ring are about 7.44 Å at entrance, 9.91 Å at the central of the cavity, respectively. The structural integrity and stability of the metallacrown ring were studied by electronspray ionization ESI-MS and UV–Vis spectroscopy. The results show that it is stable and soluble in methanol. Antibacterial screening data show that the complex 2 weakened dramatically the antibacterial activity of the ligand H3st.