A SYNTHETIC IRON-CONTAINING PRISMANE COMPLEX - PECULIAR ELECTRON-DELOCALIZATION AND SPIN-COUPLING PROPERTIES DEDUCED FROM MOSSBAUER AND MAGNETIZATION STUDIES

The prismane complex (Et4N)(3)[Fe6S6Cl6] was investigated by Mossbauer spectroscopy under various experimental conditions, i.e. at temperatu res 0.3-250 K in a field of 20 mT (perpendicular to gamma), at 300, 60 0 and 900 mK in a field of 1T ( perpendicular to gamma), and at 4.2 an d 100 K in a field of 6.1 T ( parallel to gamma). The obtained tempera ture dependences of the quadrupole splitting, asymmetry parameter and line shape are described successfully in terms of electron tunneling b elow and electron hopping above 10 K. The temperature variation of the magnetic hyperfine splitting is analyzed in terms of the stochastic t heory of relaxation with two contributions, i.e. spin relaxation among the substates of the S-tot = 1/2 Kramers system and pairwise spin fli ps within the prismane cluster keeping the orientation of the total cl uster spin preserved. Magnetization measurements in the temperature ra nge 2-295 K are analyzed with a spin-Hamiltonian which includes explic itly superexchange and double exchange contributions. Both the analysi s of the Mossbauer measurements and the analysis of the magnetization measurements reveal peculiar electron-delocalization and spin-coupling properties of the prismane cluster, i.e. three 'excess' electrons are delocalized over three metal pairs and the spin of the three metal pa irs couples to the total cluster spin S-tot = 1/2. (C) 1998 Elsevier S cience S.A. All rights reserved.