Experimental spin density in the high spin ground state of the Fe8pcl cluster

The induced spin density was determined by polarised neutron diffraction in the S = 10 ground state of [(tacn)6Fe8O2(OH)12]Br4.3(ClO4)3.7 · 6H2O, Fe8pcl, which differently from the bromide analogous, Fe8Br8, presents a centre of symmetry. The relative spin arrangement is in agreement with the model proposed from classical magnetic measurements and with the previous spin density study in the noncentrosymmetrical Fe8Br8 compound. The experimental spin populations on the iron atoms are in good quantitative agreement with calculations using exact diagonalisation of the exchange Hamiltonian with experimental J values obtained from magnetic susceptibility measurements on Fe8Br8. This determination confirms that the spin density determination provides a valuable evaluation of the relative strengths (and sign) of the intracluster magnetic interactions and that the dissymmetry observed on the spin populations in the Fe8Br8 compound with respect to quasi-D2 symmetry of the molecular frame was an artefact due to the data refinement method for non centrosymmetrical structures.