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

The trianionic heptadentate ligand, (Z)-3-(salicylhydrazinocarbonyl) propenoic acid ((Z)-H(4)shcpa) (1), has been synthesized in good yield and reacted with FeCl(3).6H(2)O, to produce the complex [Fe(III)(6) (C(12)H(9)N(2)O(5))(6)(H(2)O)(2)(CH(3)OH)(4)] x 6CH(3)OH (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)-H(3)mshcp) (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 Fe(3+) ions, the ligands enforce the stereochemistry of the Fe(3+) ions as a propeller configuration with alternating Lambda/Delta form. The metallacrown can be treated with SnCl(2) to obtain purified ester. In addition, we have also obtained reduced esterified ligand, methyl 3-(salicylhydrazinocarbonyl) propanoate (H3mshcp) (4) with another reductant Zn powder.