Esterification and isolation of the carboxylic acid with salicyl-bis-hydrazide via coordination of iron(III) 18-metallacrown-6 complex

The trianionic heptadentate ligand, (Z)-3-(5'-bromosalicylhydrazinocarbonyl) propenoic acid ((Z)-H4bshcpa), has been synthesized in good yield and reacted with FeCl3 center dot 6H2O to produce [FeIII6(C12H8N2O5Br)6(H2O)2(CH3OH)4] center dot 8H2O center dot 8CH3OH. 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-(5'-bromosalicylhydrazinocarbonyl) propenoate ((Z)-H3mbshcp). In the crystal structure, the neutral Fe(III) complex contains an 18-membered metallacrown ring consisting of six Fe(III) and six trianionic ligands. The 18-membered metallacrown ring is formed by six structural moieties of the type [Fe(III)-N-N]. Due to the meridional coordination of the ligands to Fe3+, the ligands enforce stereochemistry of the Fe3+ ions as a propeller configuration with alternating / forms. The metallacrown can be treated with SnCl2 to obtain purified ester. In addition, we have also obtained reduced esterified ligand, methyl 3-(5'-bromosalicylhydrazinocarbonyl) propanoate (H3mbshcp), with Zn powder as reductant.