Iron(iii) coordination induced novel 18-metallacrown-6 complex: esterification and isolation of the ligand

Abstract

The trianionic heptadentate ligand, (Z)-3-(salicylhydrazinocarbonyl) propenoic acid ((Z)-H₄shcpa) (1), has been synthesized in good yield and reacted with FeCl₃·6H₂O, to produce the complex [Fe^III₆ (C₁₂H₉N₂O₅)₆(H₂O)₂(CH₃OH)₄]·6CH₃OH (2). The complex has been characterized by single-crystal X-ray diffraction. In the self-assembly process the ligand was esterified and transferred into (Z)-methyl 3-(salicylhydrazinocarbonyl) propenoate ((Z)-H₃mshcp) (3). In the structure, the neutral Fe(III) complex contains 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 form. The metallacrown can be treated with SnCl₂ to obtain purified ester. In addition, we have also obtained reduced esterified ligand, methyl 3-(salicylhydrazinocarbonyl) propanoate (H₃mshcp) (4) with another reductant Zn powder.