CRYSTAL AND MOLECULAR-STRUCTURE, MAGNETIC-PROPERTIES AND SCATTERED-WAVE DESCRIPTION OF THE ELECTRONIC-STRUCTURE OF THE HEXANUCLEAR OCTAHEDRAL CLUSTERS [FE-6(MU(3)-S)(8)(PET(3))(6)][PF6](N) (N=1 OR 2)

The crystal structure of [Fe-6(mu(3)-S)(8)(PEt(3))(6)][PF6](2) has been determined. It is isostructural with the parent tetraphenylborate complex. The electronic structures of [Fe-6(mu(3)-S)(8)(PEt(3))(6)][PF6] and of [Fe-2(mu(3)-S)(8)(PEt(3))(6)][PF6](2) have been investigated experimentally by measuring the temperature variation of the magnetic susceptibility between 300 and 4.2 K, the field dependence of the magnetisation at three different temperatures in the range 2-10 K and the polycrystalline powder Mossbauer spectra at variable temperature. The complex [Fe-6(mu(3)-S)(8)(PEt(3))(6)][PF6] posses a S = 7/2 spin state well isolated from the excited states, while [Fe-6(mu(3)-S)(8)(PEt(3))(6)][PF6](2) shows a marked temperature dependence of the magnetic susceptibility. The magnetic structures of the complexes have been characterised empirically with the Heisenberg-Dirac-van Vleck exchange spin Hamiltonian. The nature of the magnetic states is rationalised in the framework of X alpha-SW theory.