Two novel 18-metallacrown-6 complexes: Synthesis, structural characterization and bioactivity

Two new macrocyclic hexanuclear metal(III) 18-metallacrowns-6, [Mn6(acshz)6(H2O)6] · 18H2O (1) and [Fe6(acshz)6(CH3OH)6] · 6CH3OH · 6H2O (2), have been synthesized and characterized, where acshz3− is N-acetyl-5-chlorosalicylhydrazidate. These crystal structures contain neutral 18-membered metallacrown rings consisting of six metal(III) ions and six acshz3− ligands. The ring is formed by the succession of six structural moieties of the type [M(III)–N–N] through hydrazide N–N groups bridging the ring metal ions. The ligand enforces the metal ions to form the stereochemistry of a propeller configuration with alternate Λ/Δ or Δ/Λ forms. The largest diameters of the hexanuclear rings are about 6.97 Å at the entrance and 9.53 Å at the centre of the cavity for 1; and 7.94 and 10.24 Å for 2, respectively. The solution integrity and stability of the metallacrowns were confirmed using electrospray ionization ESI-MS and UV–Vis spectroscopy in methanol. Antibacterial screening data indicate the formation of the metallacrown 1 reduces the antimicrobial activity of the ligand H3acshz hugely, while metallacrown 2 has strong antimicrobial activity against Bacillus subtilis (B. subtilis).

Two new 18-metallacrown-6 complexes, [Mn6(acshz)6(H2O)6] · 18H2O (1) and [Fe6(acshz)6(CH3OH)6] · 6CH3OH ·  6H2O (2), have been prepared using N-acetyl-5-chlorosalicylhydrazidate (acshz3−) and characterized. The integrity and stability of the metallacrown in methanol has been confirmed by ESI-MS and UV–Vis spectroscopy. Antibacterial screening data showed that the iron metallacrown 2 has strong antimicrobial activity against Bacillus subtilis.Figure optionsDownload as PowerPoint slide