Synthesis, Crystal Structure, and Bioactivity of a Novel Iron(III) 18-Metallacrown-6 Complex

A macrocyclic hexanuclear iron(III) 18-metallacrown-6 compound, [Fe-6(H2O)(6) (abshz)(6)]center dot 38H(2)O, has been prepared using a trianionic pentadentate ligand N-acetyl-5-bromosalicylhydrazidate (abshz(3-)) and characterized by X-ray diffraction. The crystal structure contains a neutral 18-member metallacrown ring consisting of six Fe(III) and six abshz(3-) ligands. The 18-member metallacrown ring is formed by the succession of six structuralmoieties of the type [Fe(III)-N-N]. Due to the meridional coordination of the ligand to the Fe3+ ion, the ligand enforces the stereochemistry of the Fe3+ ions as a propeller configuration with alternating Lambda/Delta forms. The disc-shaped hexanuclear ring shows at its largest diameter about 7.27 angstrom at entrance and about 9.80 angstrom at the center of the cavity. Antibacterial screening data showed that the iron metallacrown has strong antimicrobial activity against Bacillus subtilis and Staphylococcus aureus.