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.