Esterification of the ligand: Synthesis, characterization and crystal structure of a iron(III) 18-metallacrown-6 complex with methyl 4-(5′-chlorosalicylhydrazinocarbonyl) butyrate

The multidentate ligand, 4-(5′-chlorosalicylhydrazinocarbonyl) butyric acid, has been synthesized and reacted with FeCl3 to produce the iron(III) 18-metallacrown-6 complex [FeIII6(C13H12N2O5Cl)6(CH3OH)6]·5CH3OH. In the complex the ligand 4-(5′-chlorosalicylhydrazinocarbonyl) butyric acid was esterified and transferred into methyl 4-(5′-chlorosalicylhydrazinocarbonyl) butyrate. In the crystal structure, the hexanuclear 18-membered rings of iron atoms are linked by six hydrazide N–N groups. The deprotonated and esterified ligand acts as a trianionic pentadentate ligand, one phenolate oxygen, one hydrazide nitrogen and one carbonyl oxygen in the ligand are bound to one Fe3+ cation, and the other carbonyl oxygen plus the other hydrazide nitrogen in the same ligand are chelated to an adjacent Fe3+ cation. In hydrochloric acid the metallacrown [FeIII6(C13H12N2O5Cl)6(CH3OH)6]·5CH3OH can be treated with SnCl2 to obtain purified ester methyl 4-(5′-chlorosalicylhydrazinocarbonyl) butyrate.