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

Abstract

A new tetranuclear iron(III) complex [Fe 4(μ-btppnol) 2(μ-O) 2(μ-OAc) 2](BPh 4) 2·CH 3CN(H 2O) 1/2(MeOH) 1/2 (1), (H 2btppnol= 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 H 2btppnol 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.