Synthesis, crystal structure and esterification of a novel iron(III) 18-metallacrown-6 complex

The trianionic heptadentate ligand, (Z)-3-(5′-chlorosalicylhydrazinocarbonyl) propenoic acid, has been synthesized and reacted with FeCl3·6H2O, to produce the complex [FeIII6(C12H8N2O5Cl)6(H2O)4(CH3OH)2]·8H2O·4CH3OH. In the self-assembly process the ligand was esterified and transferred into (Z)-methyl 3-(5′-chlorosalicylhydrazinocarbonyl) propenoate. In the crystal structure, the neutral Fe(III) complex contain a 18-membered metallacrown ring consisting of six Fe(III) and six trianionic ligands. The 18-membered metallacrown ring is formed by the succession of six structural moieties of the type [Fe(III)–N–N]. Due to the meridional coordination of the ligands to the Fe3+ ions, the ligands enforce the stereochemistry of the Fe3+ ions as a propeller configuration with alternating Λ/Δ forms. The metallacrown can be treated with SnCl2 or Zn powder to obtain purified ester.