Synthesis, Structure, and Magnetism of a Ferric 24-Azametallacrown-8 Complex

A new pentadentate N-isobutyrylsalicylhydrazidate ligand (H3ibushz,
C11H14N2O3) and a self-assembly synthesis of the first 24-azametallacrown-8, [Fe8(C11H11N2O3)8(CH3OH)8]·0.5CH2Cl2·7.5CH3OH·3.5H2O, have been reported. Eight Fe(III) ions and eight
deprotonated ibushz3- ligands construct a planar 24-membered
ring based on the M−N−N−M linkage. The chiralities of the iron
atoms on the 24-azametallacrown-8 ring alternate between the Λ
and Δ forms. The title octanuclear azametallacrown has no
crystallographic centrosymmetry, while all the known metallacrowns
and azametallacrowns with an even nuclear number have crystallographic centrosymmetry. The study of 1H NMR spectra suggests
that the title compound retains its metallacrown structure in solution
at room temperature over a period of at least three months. There
exists a strong antiferromagnetic exchange interaction between
the iron paramagnetic centers.