Crystal structure and magnetic properties of a new tetranuclear iron (III) complex with asymmetric iron coordination as a model for polynuclear iron proteins

A new tetranuclear iron(III) complex [Fe4(μ-btppnol)2(μ-O)2(μ-OAc)2](BPh4)2·CH3CN(H2O)1/2(MeOH)1/2 (1), (H2btppnol=N,N,N′-tris(2-pyridylmethyl)–N′–(2-hydroxybenzyl)–1,3-diaminopropan-2-ol) was synthesized and its crystal structure and magnetic properties are shown. Complex 1 is an interesting structural model for polynuclear iron enzymes, since the ligand H2btppnol is unsymmetric, and thus it may provide distinct coordination modes for the iron centers. The magnetic investigation revealed two antiferromagnetic coupling pathways, one mediated by the oxo bridge, J=−83(6) cm−1 and the other mediated by the alkoxo bridge, with J′=−8.7(5) cm−1 and similar to the J=−9 cm−1 observed for the oxidized form of purple acid phosphatases.