Synthesis and structure of [Fe13O4F24(OMe)12]5-:: The first open-shelf Keggin ion

The reaction between ferric fluoride trihydrate and pyridine in hot methanol produced yellow-brown crystals of (PyH)5·[Fe13O4F24(OMe)12]·4H2O·CH3OH. The anionic complex [Fe13O4F24(OMe)12]5- (1), which has a full Td symmetry, is the first example of an open-shell Keggin ion consisting of 13 high-spin d5 iron(III) atoms. The central, tetrahedral {FeO4} unit in 1 is surrounded by 12 octahedral iron atoms, which are bridged by methoxide oxygen atoms and fluoride ligands. In addition, each of the 12 iron atoms is coordinated to a terminal fluoride ligand with an Fe-F distance of 1.846(3) Å. Magnetic susceptibility studies indicate strong exchange interactions between the iron atoms, the μeff value of 19.3 μB at 300 K being significantly lower than that expected for thirteen uncoupled S = 5/2 centers. Copyright © 2002 American Chemical Society.