Synthesis, Structure, and Properties of an Undecairon (3) Oxo-Hydroxo Aggregate: An Approach to the Polyiron Core in Ferritin

摘要

A novel, discrete undecairon (III) oxo-hydroxo aggregate, (Fe11O6(O2CPh)15 , has been synthesized by controlled hydrolytic polymerization in nonagueous solvents of simple mononuclear and oxo-bridged binuclear ferric salts. The complex was structurally characterized in two crystalline forms. In the rhombohedral form, (Fe11O6(OH)6O2CPh)15 6THF, the molecules have crystallographically required D3 symmetry. The eleven iron atoms define a twisted, pentacapped trigonal prism. Two type A iron atoms located on the threefold symmetry axis are joined by u3-oxo bridges to six type B iron atoms are linked to one another and to three type C iron atoms, situated on twofold symmetry axes, by hydroxo bridges. A sheath of 15 bidentate bridging benzoate ligands, no two of which join Fe-O bond lengths range from 1.876 (5) Angstrom for Fe-(oxo) to 2.106 (8) angstrom for Fe-O(benzoate) type interactions. The six tetrahydrofuran molecules penetrate the sheath of benzoate ligands to form hydrogen bonds to protons on the six hydroxo ligands. The other crystalline form, (Fe11O6(OH)6(O2CPh)15 .H2O.8MeCN, is triclinic and has no imposed molecular site symmetry.